🧪 Lab Tests for Confirming Cushing’s Syndrome in Dogs and Cats – A 2025 Vet’s Guide

By Dr Duncan Houston, BVSc

🔍 When to Suspect Cushing’s Disease

Cushing’s syndrome (hyperadrenocorticism) occurs when the body produces too much cortisol. Once a dog or cat shows symptoms—like thirst, urination, hair loss, or belly bloating—specific lab tests are needed to confirm the diagnosis. 🩺

🐶 Cushing’s Disease Testing in Dogs

1. 💉 Low Dose Dexamethasone Suppression Test (LDDST)

Gold standard for confirming Cushing’s

• 🕗 Takes 8 hours in the hospital
• 🧪 Dexamethasone (a steroid) is injected IV
• 📉 Cortisol levels are measured at baseline and again 8 hours later

In a normal dog, cortisol levels will drop in response. In Cushing’s patients, cortisol stays elevated.

Advantages:

• ✅ Detects ~90% of Cushing’s cases
• 🔎 Sometimes includes a 4-hour sample for subtype classification

2. 💉 ACTH Stimulation Test

Useful for monitoring treatment and diagnosing Cushing’s caused by long-term steroid use

• ⏱️ Shorter test (1–2 hours)
• 🧪 ACTH injection → cortisol level spike is measured

Less sensitive than LDDST, but more specific (i.e., fewer false positives). Required when evaluating Cushing’s treatment. 🩺

3. 💧 Urine Cortisol:Creatinine Ratio

Screening tool only – not diagnostic

• 💡 If test is negative → Cushing’s ruled out
• ⚠️ If test is positive → further testing (LDDST or ACTH Stim) required

Sample should be collected at home to avoid stress-induced cortisol spikes. 🧪

🐱 Cushing’s Disease Testing in Cats

1. 💉 LDDST (Feline Version)

Cats are more resistant to steroids, so they require higher dexamethasone doses. The process is the same as in dogs, with 8 hours of hospitalization. 🐈

2. 💧 Urine Cortisol:Creatinine Ratio (Feline)

Highly sensitive but prone to false positives. A useful at-home screening tool when cats are too stressed by clinic visits.

How It Works:

• 💧 Owner collects urine samples over 3 mornings
• 📊 First 2 samples average the baseline cortisol:creatinine ratio
• 💊 Dexamethasone pills given at home on Day 2
• 💧 Third sample helps classify the Cushing’s type

No blood draw is needed, but sample collection may require special litter or plastic wrap over the litter tray. 🧻

🧬 Comparing the Tests

📌 When to Use Which Test

• ✅ Suspected spontaneous Cushing’s – Start with LDDST
• ✅ Long-term steroid use or treatment monitoring – Use ACTH Stimulation Test
• ✅ Too stressed for clinic tests – Start with urine test at home

⚠️ Important Considerations

Cushing’s testing is not one-size-fits-all. Proper diagnosis means choosing the right test based on symptoms, meds, and species. Avoid early treatment until diagnostic confirmation is made. Treatment depends heavily on whether the form is pituitary-based or adrenal. 🎯

📲 Ask A Vet for Cushing's Diagnosis Support

Need help deciding which test your pet needs or interpreting your results? Connect directly with expert veterinary support through the Ask A Vet App or at AskAVet.com. We’ll guide you every step of the way. 🐶📱🐱

✅ Summary: Key Takeaways

• 🧬 Cushing’s is confirmed through hormone testing
• 🧪 LDDST is the most sensitive and accurate in most cases
• 📊 ACTH Stim is used for treatment monitoring or iatrogenic suspicion
• 💧 Urine cortisol:creatinine ratio is useful as an at-home screening test

💬 Final Words from Dr Duncan Houston

Cushing’s disease can mimic many other conditions, and no single test fits all pets. That’s why proper diagnostics, in partnership with your veterinarian, are essential. Whether your pet needs lab testing, follow-up curves, or treatment adjustments, we’re here to help. 🐾🩺

For real-time help, open the Ask A Vet App or visit AskAVet.com. Your pet’s wellness is our mission. 🐕🐱📱