Why Is My Diabetic Cat’s Blood Sugar Still High Despite Insulin?

By Dr Duncan Houston

Watching your cat’s glucose remain high while the insulin dose keeps climbing is frustrating and worrying. It can feel as though the insulin is not working, but that is not always what is happening.

In practice, a difficult diabetic cat usually falls into one of three groups. The insulin is not being delivered or handled as intended, the glucose results are making the control look worse than it really is, or another disease is creating genuine insulin resistance.

The solution is not to keep increasing insulin blindly. It is to work through these possibilities in the correct order.

Quick Answer

A diabetic cat is considered difficult to regulate when excessive thirst, urination, hunger, weight loss or poor wellbeing continue despite an appropriate insulin plan and reliable monitoring.

For cats receiving common twice-daily insulins such as glargine U-100 or protamine zinc insulin, current AAHA guidance recommends investigating insulin technique and underlying disease if the cat is not regulated with 4 units or less every 12 hours before continuing to increase the dose. This is a trigger for investigation, not proof of severe insulin resistance.

The first step is to confirm that the insulin is being stored, prepared, measured and injected correctly. If technique is reliable, the next priorities are continuous glucose monitoring, assessment of diet and body weight, medication review and investigation for conditions such as pancreatitis, dental disease, infection, chronic intestinal disease, hyperthyroidism, kidney disease, Cushing’s syndrome and hypersomatotropism.

What Does “Hard to Regulate” Mean?

There is no single blood glucose number or insulin dose that diagnoses poor regulation.

A cat may be inadequately regulated when several of the following continue despite treatment:

• Excessive thirst

• Large volumes of urine

• Constant hunger

• Progressive weight loss

• Loss of muscle

• Diabetic neuropathy or a dropped-hock stance

• Persistent glucosuria

• Recurrent ketones

• Wide glucose fluctuations

• Repeated hypoglycaemic episodes

• Failure to improve after appropriate insulin adjustments

• A steadily increasing insulin requirement

A cat with high glucose readings but normal thirst, normal urine production, stable body weight, good appetite and comfortable behaviour may be better controlled than the numbers initially suggest.

Current AAHA guidance specifically notes that some clinically well cats maintain or gain weight despite continuous glucose monitor readings that remain between approximately 250 and 350 mg/dL. Increasing insulin solely to improve the graph may place these cats at unnecessary risk of hypoglycaemia.

How Worried Should You Be?

Level	What you may notice	What to do
Stable but needs review	Glucose readings remain high, but your cat is bright, eating and maintaining weight	Continue the prescribed dose and arrange a planned review rather than increasing insulin yourself
Poorly regulated	Persistent thirst, urination, hunger or weight loss despite several weeks of treatment	Arrange a veterinary reassessment within the next few days
Possible insulin resistance	The dose is approaching or exceeding 4 units every 12 hours with persistent clinical signs	Investigate administration, glucose trends, medication and concurrent disease before further increases
Urgent	Reduced appetite, vomiting, ketones, dehydration, marked lethargy or worsening weakness	Seek same-day veterinary assessment
Critical	Collapse, seizures, inability to stand, severe weakness, abnormal breathing or reduced consciousness	Go to an emergency veterinary hospital immediately

The 4-unit threshold is most useful for cats receiving conventional twice-daily insulin protocols. Glargine U-300 is a basal insulin with a different dosing and monitoring approach, so its dose must be interpreted separately.

Does High Blood Glucose Always Mean the Insulin Dose Is Too Low?

No.

One high reading can be caused by:

• Stress

• Recent food intake

• A missed dose

• A fur shot

• Poorly mixed insulin

• A damaged test strip

• A sensor error

• A poorly timed spot check

• Inadequate insulin duration

• Day-to-day glucose variation

• Another illness

• Too much insulin creating unstable glucose patterns

Cats can develop marked stress hyperglycaemia, even during home monitoring when sampling becomes a wrestling match. Glucose results must be interpreted alongside the cat’s thirst, urine output, appetite, weight and general wellbeing.

This is why current feline guidance recommends monitoring the cat rather than chasing a perfect set of numbers. Routine in-clinic glucose curves are no longer recommended for most cats because hospital stress can significantly affect the result. Continuous glucose monitors usually provide a more complete picture.

Is the Somogyi Effect Causing High Glucose?

The traditional Somogyi theory states that excessive insulin causes hypoglycaemia, which then triggers counter-regulatory hormones and rebound hyperglycaemia.

Current iCatCare guidance states that there is no evidence supporting a true Somogyi effect in cats.

Cats can still experience substantial glucose variability, and excessively rapid insulin increases can produce periods of hypoglycaemia followed by high readings later in the day. However, this should not automatically be labelled Somogyi rebound.

The practical lesson remains important: a high glucose result does not prove that more insulin is needed. A continuous glucose monitor may reveal that the cat is dropping too low at another point in the dosing interval.

Step 1: Confirm That the Cat Is Truly Poorly Regulated

Before investigating rare hormonal diseases, look at the complete clinical pattern.

Record the cat’s clinical response

Track:

• Daily water consumption when practical

• Number and size of urine clumps

• Appetite

• Body weight

• Muscle condition

• Activity

• Ability to jump and walk

• Vomiting

• Stool quality

• Insulin dose and time

• Missed or uncertain injections

• Any suspected fur shots

• Glucose and ketone results

Improvement in excessive drinking and urination, stabilisation of weight and better energy are meaningful signs of regulation even when glucose remains above a theoretical ideal range.

Confirm the original diabetes diagnosis

Feline diabetes should be supported by persistent hyperglycaemia, glucosuria and compatible clinical signs. One high clinic glucose result can be caused entirely by stress.

Fructosamine, home blood glucose monitoring, a continuous glucose monitor or home-collected urine may help distinguish true diabetes from stress hyperglycaemia when the original diagnosis remains uncertain.

Assess glucose across several days

A continuous glucose monitor can reveal:

• Overnight hypoglycaemia

• Whether insulin has any measurable effect

• The lowest glucose concentration

• How long the insulin lasts

• Major day-to-day variability

• Whether low readings are occurring before high readings

• Whether the cat may be approaching remission

A traditional home curve provides only a snapshot of one day. A continuous monitor is not perfect, particularly at low glucose concentrations, but it generally provides substantially more useful information than isolated clinic readings.

Step 2: Audit the Insulin Before Blaming the Cat

This is the least glamorous part of the investigation and often the most productive.

A technically perfect diagnostic work-up is not much help when the insulin has quietly been landing in the fur for three weeks.

Confirm the exact insulin

Record:

• Insulin name

• Concentration

• Current dose

• Frequency

• Date first opened

• Storage conditions

• Syringe or pen being used

Do not identify insulin only by the colour of the box or cap.

Match the syringe to the insulin

A U-40 insulin must be measured with a U-40 syringe.

A U-100 insulin must be measured with a U-100 syringe.

Using a mismatched syringe can cause a major overdose or underdose. The veterinary team should watch the owner draw the prescribed dose rather than simply asking whether they understand the process.

Check how the insulin is mixed

Different insulins require different handling.

• Protamine zinc insulin is generally gently rolled or inverted until uniformly suspended.

• Porcine lente insulin must be mixed according to its product instructions and usually requires thorough shaking.

• Glargine is a clear solution and should not be shaken or mixed.

• Glargine U-300 remains in its dedicated pen and should not be withdrawn with a syringe.

Inconsistent resuspension can cause the concentration drawn from the same vial to vary from one injection to the next.

Check pen technique

For insulin pens, confirm that the owner:

• Attaches a new needle

• Primes the pen before each dose

• Reads the dose window correctly

• Inserts the needle completely through the coat

• Holds the injection button down for the recommended time

• Removes the needle after use

• Does not count clicks instead of reading the dose window

Failure to prime the pen or withdrawing it too quickly may result in partial or missed doses.

Watch an injection

The veterinary team should watch the owner administer sterile saline using their usual technique.

This can identify:

• Needles passing through both sides of the skin tent

• Injections placed into the coat

• Inadequate needle penetration

• Incorrect pen positioning

• Poor syringe control

• Difficulty restraining the cat

• Doses being lost during struggling

Videoing a normal home injection can also be useful because some cats behave very differently in the clinic.

Prevent missed and duplicate doses

When several people care for the same cat, use:

• A written medication log

• A shared app

• A whiteboard

• A physical marker moved after each injection

• Initials beside every administered dose

One family member missing a dose while another occasionally gives it twice creates a glucose profile that can make even an endocrinologist contemplate a career change.

Check whether the insulin may have lost potency

Insulin can become unreliable after:

• Freezing

• Overheating

• Prolonged direct sunlight

• Incorrect storage

• Contamination

• Repeated vigorous handling when not appropriate

• Extended use beyond the product’s recommended period

• Damage to the vial or pen

Follow the product-specific storage and discard instructions. When technique appears correct but the response changes unexpectedly, replacing the vial or pen may be a reasonable troubleshooting step.

Step 3: Review Food, Weight and Routine

Is the cat eating more food than the owner realises?

Common hidden calorie sources include:

• Another pet’s food

• Unmeasured dry food

• Treats

• Table food

• Food provided by neighbours

• Hunting

• Several family members each providing a “small” snack

Food access does not make insulin stop working, but a changing carbohydrate or calorie intake can make glucose control unpredictable.

Is the cat overweight?

Obesity is a common and reversible cause of insulin resistance in cats.

An overweight diabetic cat should lose weight gradually using a measured, complete diet and a veterinary weight plan. Rapid restriction is unsafe and can contribute to muscle loss, poor food intake or hepatic lipidosis.

Even modest weight loss can improve insulin sensitivity and may increase the chance of diabetic remission.

Has the diet recently changed?

Changing from a higher-carbohydrate food to a lower-carbohydrate diet can reduce insulin requirements.

This may be beneficial, but the dose may need to fall quickly. A major dietary change should therefore be accompanied by appropriate glucose monitoring rather than waiting several weeks for the next routine test.

Glycaemic variability may be greater in cats eating dry food, particularly when dry food is freely available throughout the day. However, food acceptance and adequate calorie intake remain more important than forcing a diabetic diet that the cat refuses to eat.

Step 4: Review Every Medication

Glucocorticoids are an important cause of insulin resistance and can contribute to feline diabetes.

Relevant products may include:

• Prednisolone tablets

• Steroid injections

• Ear drops

• Eye drops

• Skin creams or sprays

• Inhaled asthma medication

• Long-acting depot preparations

• Steroid products prescribed by another clinic

Progestogen medication can also cause insulin resistance and predispose cats to diabetes.

Do not stop a medically necessary steroid abruptly. Long-term glucocorticoid treatment may need to be tapered, and uncontrolled asthma, intestinal disease or skin disease will create problems of its own.

When the underlying condition allows an insulin-resistance-causing medication to be withdrawn, AAHA guidance recommends reassessing diabetic control after approximately two weeks before automatically escalating insulin again.

Step 5: Look for Concurrent Disease

Pain, inflammation, infection and hormonal disease can all reduce insulin sensitivity.

Common conditions include:

Possible cause	Clues that may be present	Possible investigation
Dental disease	Bad breath, drooling, reduced grooming, chewing on one side or no obvious signs at all	Detailed oral examination and dental imaging when indicated
Pancreatitis	Reduced appetite, vomiting, lethargy, abdominal discomfort or fluctuating glucose	Feline pancreatic lipase, ultrasound and supportive clinical findings
Chronic intestinal disease	Vomiting, diarrhoea, weight loss, reduced appetite or low cobalamin	Cobalamin, folate, TLI, fPLI, ultrasound and further gastrointestinal testing
Kidney disease	Weight loss, increased thirst, dehydration, reduced appetite or dilute urine	Blood chemistry, SDMA where available, urinalysis and blood pressure
Hyperthyroidism	Weight loss, increased appetite, restlessness, rapid heart rate or thyroid enlargement	Total T4 and additional thyroid testing when needed
Bacterial infection	Fever, urinary signs, skin disease, wounds or respiratory signs	Examination and targeted culture or imaging
Obesity	Increased body fat and reduced activity	Body condition scoring and measured weight-management plan
Cancer or chronic inflammation	Weight loss, appetite change, abnormal examination or unexplained laboratory changes	Imaging and targeted diagnostics
Hypersomatotropism	Poor regulation, weight gain despite diabetes, extreme hunger, broad facial changes or no obvious external signs	IGF-1 followed by CT or MRI when appropriate
Cushing’s syndrome	Fragile skin, pendulous abdomen, bruising, poor hair growth or muscle loss	Endocrine testing and adrenal or pituitary imaging

AAHA recommends considering dental disease, bacterial infection, pancreatitis, inflammatory bowel disease and hypersomatotropism when insulin-treated cats remain hyperglycaemic despite dose increases. Gastrointestinal testing, abdominal ultrasound and targeted hormonal testing may then be appropriate.

Are Urinary Tract Infections Common in Diabetic Cats?

A genuine urinary tract infection can increase insulin resistance and should be treated appropriately.

However, diabetic cats should not automatically receive repeated urine cultures or antibiotics simply because glucose is present in the urine.

Current feline guidance states that urine culture is most appropriate when the cat has lower urinary tract signs, such as straining or frequent small urinations, together with an active urine sediment. Subclinical bacteriuria without urinary signs does not normally require antibiotic treatment.

Signs that justify further urinary investigation include:

• Straining to urinate

• Frequent small urinations

• Blood in the urine

• Urinating outside the litter tray

• Pain while urinating

• Fever

• An active inflammatory urine sediment

Treatment should be guided by bacterial culture and susceptibility testing rather than chosen blindly.

Hypersomatotropism: The Most Important Hormonal Cause

Hypersomatotropism is caused by excessive growth hormone, usually produced by a pituitary tumour.

The term acromegaly describes the characteristic physical changes caused by prolonged growth hormone exposure. Hypersomatotropism is the more accurate general term because many affected cats have no obvious acromegalic appearance.

Current iCatCare guidance estimates that hypersomatotropism may affect between one in five and one in three diabetic cats. It is the leading endocrine cause of clinically important insulin-resistant diabetes in cats.

Does a cat need to look acromegalic?

No.

Approximately 75% of diabetic cats with hypersomatotropism do not have distinctive physical changes that clearly separate them from other diabetic cats.

A normal-looking face and paws do not rule it out. Some affected cats are also regulated on relatively ordinary insulin doses, while others require very high doses.

Signs that increase suspicion

Possible signs include:

• Extreme hunger

• Weight gain despite persistent hyperglycaemia

• Broadening of the face

• Increased spacing between the front teeth

• A protruding lower jaw

• Large or “clubbed” paws

• Enlarged kidneys or liver

• Noisy breathing or respiratory stridor

• Heart enlargement or cardiomyopathy

• A heart murmur

• Stiffness or reduced mobility

• Increasing insulin requirements

The absence of these signs does not exclude the disease.

How is hypersomatotropism screened?

The main screening test is serum insulin-like growth factor 1, or IGF-1.

An IGF-1 concentration above approximately 1,000 ng/mL is strongly supportive of hypersomatotropism when the clinical situation is compatible. Results between approximately 700 and 1,000 ng/mL may fall within a grey zone and may need to be repeated. Laboratory interpretation ranges can differ.

Why should IGF-1 not be measured immediately?

Insulin is needed for normal production of IGF-1 by the liver. A newly diagnosed, insulin-deficient cat can therefore have a misleadingly low IGF-1 result.

AAHA advises waiting at least four to six weeks after insulin treatment begins when hypersomatotropism is suspected. The iCatCare consensus suggests that measurement after six to eight weeks of diabetes treatment may be more reliable.

Uncontrolled hyperthyroidism can also reduce IGF-1, while obesity may increase it. These factors must be considered when interpreting the result.

Does a high IGF-1 confirm a pituitary tumour?

A strongly elevated result provides substantial evidence of hypersomatotropism, but CT or MRI may be recommended to assess the pituitary gland and plan treatment.

A normal scan does not completely exclude the disease because very small tumours or pituitary hyperplasia may not be visible.

Can hypersomatotropism be treated?

Options may include:

• Transsphenoidal hypophysectomy

• Radiation therapy

• Selected medical treatments

• Management of the diabetes and other consequences without treating the pituitary lesion directly

Hypophysectomy offers the strongest chance of controlling growth hormone and achieving diabetic remission but is available only through a small number of specialist centres. Radiation may reduce tumour size and insulin requirements but has a less predictable effect on hormone production.

Could It Be Cushing’s Syndrome?

Feline Cushing’s syndrome, or hypercortisolism, is much less common than hypersomatotropism.

Most affected cats are diabetic, but they usually have additional clinical clues such as:

• Fragile or easily torn skin

• Thin skin

• Poor hair regrowth

• Symmetrical hair loss

• Prominent abdominal veins

• A pendulous abdomen

• Muscle wasting

• Bruising

• Slow wound healing

• Weight gain or weight loss

Diagnosis requires a compatible clinical presentation, endocrine testing and appropriate imaging. An abnormal cortisol test in a cat with no supportive clinical signs should be interpreted cautiously because uncontrolled diabetes and other illness can interfere with endocrine testing.

Could Hyperthyroidism Be Causing Poor Regulation?

Yes.

Hyperthyroidism can contribute to insulin resistance and can also cause weight loss despite a good appetite, making diabetic control appear worse.

A total T4 should be included in the assessment of a mature or senior diabetic cat, particularly when there is:

• Ongoing weight loss

• Restlessness

• Increased vocalisation

• Vomiting or diarrhoea

• Rapid heart rate

• A palpable thyroid gland

A normal T4 result may need to be repeated when the clinical suspicion remains high because concurrent illness can suppress thyroid hormone into the reference interval. Total T4 is part of the recommended minimum evaluation for diabetic cats.

Could Insulin Antibodies Be the Cause?

Insulin antibodies can develop in insulin-treated cats, but clinically important antibody-mediated insulin resistance appears to be rare.

Studies have identified insulin antibodies in some treated cats without finding a consistent relationship between antibody concentrations and diabetic control. Individual severe cases have been reported, but antibody testing should generally be considered only after administration problems, hypersomatotropism and more common concurrent diseases have been investigated.

Switching insulin solely because antibodies are suspected is therefore unlikely to be the best first step.

What Tests Does a Difficult Diabetic Cat Need?

The investigation should be selected according to the cat rather than ordering every test simultaneously.

First-level assessment

A useful starting investigation commonly includes:

• Complete history

• Full physical examination

• Accurate body weight

• Body and muscle condition scoring

• Dental and oral assessment

• Review of insulin handling and administration

• Review of all food, treats and medication

• Complete blood count

• Serum biochemistry

• Electrolytes

• Cholesterol and triglycerides

• Urinalysis with sediment examination

• Total T4

• Fructosamine where useful

• Blood or urine ketones when the cat is unwell

• Continuous glucose monitoring when available

AAHA recommends a CBC, chemistry panel, electrolytes, lipids, urinalysis and total T4 as part of the diabetic evaluation, with blood beta-hydroxybutyrate measurement in newly diagnosed or clinically unwell cats.

Second-level assessment

Depending on the findings, further testing may include:

• Feline pancreatic lipase

• Trypsin-like immunoreactivity

• Cobalamin

• Folate

• Quantitative urine culture when urinary signs are present

• Abdominal ultrasound

• Thoracic imaging

• Echocardiography

• IGF-1

• Cushing’s testing

• Pituitary CT or MRI

• Adrenal imaging

• Biopsy or other investigation of identified masses

A substantially underweight or muscle-wasted cat deserves particular investigation for pancreatitis, chronic enteropathy, hyperthyroidism, pancreatic insufficiency and neoplasia rather than simply receiving more insulin.

What Should Treatment Focus On?

Correct administration problems

This may involve:

• Replacing the insulin

• Matching the correct syringe

• Retraining injection technique

• Changing needle length

• Improving pen technique

• Creating a shared dose log

• Correcting storage or mixing

• Establishing a reliable schedule

Treat concurrent disease

Dental treatment, control of pancreatitis, management of chronic intestinal disease, treatment of symptomatic infection or control of hyperthyroidism may substantially reduce insulin requirements.

When insulin resistance improves, the old insulin dose can suddenly become excessive. Glucose monitoring is therefore particularly important after treating an underlying condition.

Address obesity carefully

A measured weight-loss plan can improve insulin sensitivity, but calorie restriction must be gradual.

Monitor:

• Body weight

• Muscle condition

• Food intake

• Glucose trends

• Insulin requirement

The insulin dose may need to fall as weight and insulin sensitivity improve.

Adjust insulin using complete information

Insulin adjustments should consider:

• Clinical signs

• Body-weight trend

• CGM or home glucose data

• Lowest glucose concentration

• Duration of insulin effect

• Hypoglycaemic episodes

• Fructosamine trends

• Food intake

• Concurrent disease

For glargine U-100 and PZI, AAHA recommends an initial glycaemic assessment approximately five to seven days after treatment begins, with subsequent adjustments every five to seven days when complete information is available. More conservative changes and ten to fourteen-day intervals may be appropriate when home information is limited.

Should the Cat Change Insulin?

Possibly, but only after the major correctable causes have been investigated.

Changing insulin may be reasonable when:

• The current insulin consistently has an inadequate duration

• The formulation cannot be mixed or administered reliably

• The cat has excessive variability despite careful use

• The insulin is unsuitable for the cat’s physiology or household routine

• No concurrent disease has been identified

• Regulation remains poor after appropriate adjustments

Current AAHA guidance recommends considering another insulin when technique has been confirmed, concurrent disease has been assessed and the cat remains unregulated.

When switching, the new insulin should normally be started at an appropriate standard starting dose rather than transferring the cat directly onto an equivalent high numerical dose. For glargine U-100 or PZI, an example starting point is approximately 1 unit per cat every 12 hours, adjusted by the treating veterinarian.

Should Short-Acting and Long-Acting Insulin Be Combined?

Not as routine long-term home treatment.

Short-acting insulin has important uses in hospital, particularly during diabetic ketoacidosis. Combining short-acting and long-acting insulin at home creates greater complexity and a higher risk of hypoglycaemia.

This should only be considered under specialist direction for a carefully selected patient with intensive glucose monitoring.

For most difficult diabetic cats, finding the administration problem or underlying disease is safer and more useful than adding another insulin.

Should an Oral Diabetes Medication Be Added?

Not routinely.

SGLT2 inhibitors are established treatment options for carefully selected diabetic cats, but they are not simply harmless oral additions to an existing insulin dose.

In cats with hypersomatotropism, early studies suggest that an SGLT2 inhibitor may improve diabetic control. However, current AAHA guidance recommends specialist consultation before combining an SGLT2 inhibitor with insulin because the risk of hypoglycaemia can be extremely high and the ideal protocol is not yet established.

SGLT2 inhibitors also carry a risk of euglycaemic diabetic ketoacidosis. This means a cat can develop dangerous ketosis and acidosis without having dramatically elevated blood glucose.

Never add an oral diabetes medication or reduce insulin to accommodate it without a veterinarian-directed transition and ketone-monitoring plan.

Is a High Insulin Dose Always Dangerous?

No.

Some cats with genuine insulin resistance, particularly hypersomatotropism, require substantial insulin doses to control clinical signs. A high numerical dose is not automatically inappropriate when:

• Administration has been verified

• Glucose trends are known

• Hypoglycaemia has been excluded

• The underlying cause has been investigated

• Increases are gradual

• The cat is closely monitored

The danger arises when a high dose is based on isolated high readings or when the cause of insulin resistance suddenly improves.

For example, insulin requirements may fall rapidly after:

• Treating infection or inflammation

• Stopping an insulin-resistance-causing medication

• Weight loss

• Treating hyperthyroidism

• Pituitary surgery

• Radiation treatment

• Spontaneous diabetic remission

Cats receiving high doses therefore need a clear hypoglycaemia plan and close monitoring whenever another condition is treated.

When Is Poor Diabetic Regulation an Emergency?

High glucose alone is not always an emergency. A sick diabetic cat is.

Seek urgent veterinary care if your cat develops:

• Reduced or absent appetite

• Repeated vomiting

• Marked lethargy

• Dehydration

• Rapid weight loss

• Weakness

• Positive ketones with illness

• Rapid or abnormal breathing

• Collapse

• Severe diarrhoea

• Inability to stand

• Reduced consciousness

These signs may indicate diabetic ketoacidosis.

DKA is caused by inadequate effective insulin action combined with increased ketone production, dehydration, acidosis and electrolyte abnormalities. It can occur in newly diagnosed cats or in cats already receiving treatment, particularly when pancreatitis, infection, kidney disease or another illness is present.

Hypoglycaemia is also an emergency

Signs include:

• Sudden hunger

• Restlessness

• Weakness

• Wobbliness

• Trembling

• Strange behaviour

• Vomiting

• Collapse

• Seizures

• Unconsciousness

If your cat is alert and able to swallow, offer food and contact a veterinarian.

If your cat is weak, poorly responsive or unable to eat, rub a small amount of plain glucose or honey onto the gums and travel to an emergency clinic. Do not pour liquid down the throat or force food into an obtunded cat.

A warning for cats receiving SGLT2 inhibitors

Normal or moderately elevated glucose does not rule out euglycaemic DKA.

A cat receiving an SGLT2 inhibitor that becomes inappetent, vomits, loses weight, becomes dehydrated or develops ketones requires urgent assessment even when the glucose result does not look particularly high.

What Should You Do Next?

1. Do not increase insulin after one high result

Keep the current prescribed dose unless your veterinarian has provided a written adjustment protocol.

2. Arrange a treatment audit

Take the following to the appointment:

• Insulin vial or pen

• Syringes or pen needles

• Glucose meter

• Current food details

• Treatment log

• All medications and supplements

Demonstrate exactly how the insulin is prepared and administered.

3. Record the cat, not just the glucose

For at least several days, record:

• Appetite

• Water intake

• Urine production

• Body weight

• Insulin dose

• Injection time

• Glucose results

• Vomiting

• Stool changes

• Activity

• Any missed or uncertain doses

4. Use a continuous glucose monitor when practical

A CGM can reveal whether the problem is:

• No meaningful insulin response

• Short insulin duration

• Excessive variability

• Hidden hypoglycaemia

• Poor control only during part of the day

5. Complete the minimum medical assessment

Discuss:

• CBC

• Biochemistry

• Electrolytes

• Urinalysis

• Total T4

• Fructosamine

• Ketones

• Dental examination

• Pancreatitis assessment

• Other testing guided by clinical signs

6. Discuss IGF-1 screening

Hypersomatotropism screening should be discussed for all diabetic cats and is particularly important when regulation is poor or insulin requirements are increasing.

For a newly diagnosed cat, wait until insulin treatment has been established for at least four to six weeks, and preferably closer to six to eight weeks when practical, before relying on IGF-1.

7. Escalate to a specialist when necessary

Internal medicine referral is appropriate when:

• Insulin requirements continue increasing

• IGF-1 is elevated or equivocal

• The cat has repeated hypoglycaemia

• DKA recurs

• There is suspected Cushing’s syndrome

• Imaging identifies an adrenal or pituitary abnormality

• No explanation is found after a structured investigation

Common Mistakes to Avoid

Increasing insulin because of one high number

A single reading does not show the lowest glucose or the duration of insulin action.

Assuming every difficult case is true insulin resistance

Administration errors and inconsistent food intake are common and should be assessed first.

Blaming the Somogyi effect

Current evidence does not support classic Somogyi rebound in cats. Look for actual glucose trends instead.

Performing repeated clinic curves without considering stress

Hospital stress can produce misleading hyperglycaemia. Home monitoring or CGM is usually more informative.

Treating a positive urine culture without urinary signs

Subclinical bacteriuria generally does not require antibiotics. Treat the patient, not merely the laboratory result.

Stopping steroid medication suddenly

Glucocorticoids may worsen diabetic control, but abrupt withdrawal can be dangerous and may allow the original disease to flare.

Combining insulins at home

This is not a routine solution for persistent hyperglycaemia and can substantially increase hypoglycaemia risk.

Switching insulin at the same high dose

A new insulin may have different potency and duration. It should be started according to a new veterinary dosing protocol.

Focusing on glucose while ignoring weight and appetite

A cat losing weight or refusing food needs investigation even when the glucose graph appears acceptable.

Can Difficult Regulation Be Prevented?

Not every case can be prevented, particularly when hypersomatotropism or another hormonal disorder is present.

The risk of unstable control can be reduced by:

• Giving insulin consistently

• Using the correct syringe or pen

• Storing and preparing insulin correctly

• Recording every dose

• Keeping food intake reasonably consistent

• Maintaining a healthy body condition

• Avoiding unmeasured treats

• Monitoring body weight

• Attending early treatment rechecks

• Treating dental disease

• Reporting vomiting or appetite loss promptly

• Reviewing steroid and progestogen use

• Checking ketones when the cat is unwell

• Investigating increasing insulin requirements rather than endlessly escalating the dose

The goal is not a perfectly flat glucose line. The goal is a comfortable cat with controlled thirst and urination, stable body weight, acceptable glucose exposure and no hypoglycaemia.

Frequently Asked Questions

How many units of insulin is too much for a cat?

There is no universal maximum. However, current AAHA guidance recommends further investigation when a cat receiving a common twice-daily insulin remains unregulated at 4 units every 12 hours. Some cats with confirmed insulin resistance require much higher doses, but this should occur only with careful monitoring.

Does glucose above 300 mg/dL mean the insulin is not working?

Not necessarily. The result may reflect stress, timing, inadequate duration or a missed injection. Some clinically well cats maintain weight despite readings between 250 and 350 mg/dL. Clinical signs and glucose trends are more important than one number.

Should every diabetic cat be tested for acromegaly?

Current iCatCare guidance recommends discussing hypersomatotropism screening with caregivers of all diabetic cats because the condition is common and most affected cats do not have obvious physical changes. Testing is particularly important when regulation is poor or insulin requirements rise.

Can insulin resistance suddenly disappear?

Yes. Insulin requirements may fall after weight loss, withdrawal of a diabetogenic medication, treatment of infection or inflammation, control of hyperthyroidism or treatment of hypersomatotropism. The previous insulin dose may then cause hypoglycaemia.

Can a hard-to-regulate diabetic cat still have a good quality of life?

Yes. Many cats improve once an administration problem or concurrent disease is identified. Cats with persistent hormonal insulin resistance can also maintain a good quality of life when glucose, body weight, clinical signs and treatment burden are managed realistically.

Final Takeaway

A diabetic cat with persistently high glucose does not automatically need more insulin.

The investigation should answer three questions:

1. Is the prescribed insulin actually reaching the cat correctly?

2. Do the glucose trends and clinical signs prove that regulation is poor?

3. Is another disease or medication causing insulin resistance?

Most cats receiving conventional twice-daily insulin should be investigated before their dose moves beyond approximately 4 units every 12 hours. Hypersomatotropism deserves particular attention because it may affect one in five to one in three diabetic cats, and most affected cats do not develop an obvious acromegalic appearance.

The best approach is systematic. Confirm technique, evaluate the cat’s weight and clinical signs, obtain reliable glucose data, investigate common concurrent disease and then pursue endocrine testing where indicated.

More insulin may ultimately be required, but it should be the conclusion of the investigation, not the substitute for one.

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If your cat’s glucose remains high, insulin requirements are increasing or you are unsure whether reduced appetite, vomiting or ketones are urgent, ASK A VET™ can help you organise the treatment history and prepare the right questions for your veterinarian.