Pelger–Huët Anomaly in Cats: A Vet’s 2025 Guide to Diagnosis & Caring 🐱🩸

Greetings! I’m Dr. Duncan Houston BVSc, veterinarian and founder of Ask A Vet. In 2025, we now recognize feline Pelger–Huët anomaly (PHA) as a rare, inherited blood cell trait that’s heart‑warming to learn and simple to manage. This guide covers what it is, how to recognize it on blood smears, distinguish it from disease mimics, confirm diagnosis, understand genetics, and navigate veterinary care and monitoring.

📘 1. What Is Pelger–Huët Anomaly?

Pelger–Huët anomaly is a genetic condition where granulocyte nuclei—most notably neutrophils, eosinophils, basophils, and sometimes monocytes—fail to segment properly. Instead of the usual 3–5 lobes, these cells appear bilobed (“dumbbell”) or unilobed, sometimes round, but retain normal chromatin maturation and granulation. This condition is usually benign in heterozygous cats—most carry one affected copy and function normally—and becomes rare and more severe in homozygous individuals :contentReference[oaicite:3]{index=3}.

🔬 2. Blood Smear Appearance

On a stained blood smear you’ll spot:

• Hyposegmented nuclei: many neutrophils with only two lobes or a single round nucleus, yet normal chromatin and granule pattern :contentReference[oaicite:4]{index=4}.
• Consistent form: Most granulocytes are affected, unlike acquired “pseudo–PHA” where only a subset is unusual :contentReference[oaicite:5]{index=5}.

The images above illustrate classic bilobed and unilobed granulocytes in congenital PHA.

🌱 3. Inherited vs. Acquired

• Congenital (true PHA): Autosomal dominant pattern—heterozygous cats are normal functionally; homozygous often don’t survive :contentReference[oaicite:6]{index=6}.
• Pseudo–PHA: Acquired hyposegmentation seen in certain diseases—myelodysplasia, leukemia, infections, or drug reactions. Usually only a minority of cells are affected and often with toxic granulation :contentReference[oaicite:7]{index=7}.

🧭 4. How Diagnosis Is Made

1. Incidental finding: PHA is often first noticed during routine CBC or preoperative blood work :contentReference[oaicite:8]{index=8}.
2. Rule out disease: If granulocytes look normal otherwise—mature chromatin, no toxic changes—and clinical exam is normal, congenital PHA is suspected. Infectious/inflammatory signs suggest pseudo–PHA.
3. Family screening: Smears of parents or littermates support inheritance :contentReference[oaicite:9]{index=9}.
4. Advanced testing: Genetic testing via laminate B receptor (LBR) gene may be available; bone marrow or repeat CBC may help rule out evolving disease.

📈 5. Clinical Significance & Prognosis

• Heterozygous PHA: Benign—affected cats live healthy, normal lives with no immune defects and no increased infection risk :contentReference[oaicite:10]{index=10}.
• Homozygous PHA: Rare—usually fatal before birth or associated with skeletal defects if born :contentReference[oaicite:11]{index=11}.
• Pseudo–PHA: Indicates underlying disease—requires further diagnostic work-up.

✅ 6. Veterinary Care & Monitoring

• No treatment needed for congenital PHA.
• Owner education: Encourage sharing info with future veterinarians to avoid misinterpretation of blood results.
• Annual health checks: CBC to confirm persistence of benign pattern.
• Pseudo–PHA workup: If any infection, anemia, bone marrow issues are suspected, perform further hematology and imaging.

👨‍👩‍👦 7. Breeding Considerations

Pedigreed breeding may warrant genetic counseling.

• Heterozygous matings: 50% chance of passing allele, no health concern.
• Homozygous risk: Avoid breeding two carriers to eliminate risk of lethal homozygous offspring.

📚 8. Case Examples

“Molly,” a 14‑year‑old DSH cat, was found to have ~50% bilobed neutrophils during pre-treatment screening for hyperthyroidism. No additional signs—CBC normal otherwise, negative FeLV/FIV tests. Repeat 6 months later showed persistence. No treatment needed—lifetime of normal health followed :contentReference[oaicite:12]{index=12}.

“Leo,” a young male cat, found incidentally with unilobed neutrophils and no clinical signs. Parents’ blood smears confirmed the trait. Healthy and active post-diagnosis.

“Fake PHA” case: a cat with leukocytes showing hyposegmentation but also toxic granulation and fever—diagnosed with myelodysplastic syndrome; pseudo–PHA resolved once underlying condition treated.

🔍 9. When to Reassess

• Appearance of illness—lethargy, fever, infection.
• Changes in blood counts—anemia, thrombocytopenia, immature WBCs with toxicity.
• Sudden change in neutrophil structure or proportion—repeat smear and further workup.

✨ 10. Final Thoughts

Pelger–Huët anomaly in cats is a fascinating, harmless legacy of genetics—a quirky blood cell trait that requires no treatment and does not affect wellbeing. Knowing it’s benign helps prevent worry and unnecessary testing. And because Ask A Vet supports lifelong health management, we can guide families to monitor, document, and enjoy their feline companions without fear. 🐾❤️

For support with CBC interpretation, tele-vet follow-up, or genetic counseling, visit AskAVet.com or download the Ask A Vet app. We’re here to help you stay informed and prepared.