Polycythaemia in dogs: relative, secondary or primary
9-year-old crossbreed dog with markedly reddened mucous membranes and two seizure episodes. It is well hydrated. Abdominal ultrasound shows a mass in the left kidney.
| Parameter | Result | Reference |
|---|---|---|
| Haematocrit | 71% | 37–55 |
| Total protein | 6.6 g/dL | 5.5–7.5 |
| SpO₂ (room air) | 98% | > 95 |
| Creatinine | 1.1 mg/dL | 0.5–1.5 |
What is the most likely interpretation?
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A. Relative polycythaemia due to dehydration
The dog is well hydrated and total protein is normal; with haemoconcentration you would expect high protein. A 71% haematocrit is also too high for dehydration.
B. Appropriate secondary polycythaemia due to hypoxaemia (e.g. right-to-left shunt)
Appropriate polycythaemia is a response to tissue hypoxia, but saturation is normal here. Without hypoxaemia, erythropoietin should not be stimulated.
C. Inappropriate secondary polycythaemia due to erythropoietin production by a renal tumour
Correct. This is absolute polycythaemia with normoxaemia and a renal mass: some renal tumours (and other renal lesions) secrete erythropoietin autonomously. The seizures are explained by hyperviscosity.
D. Polycythaemia vera (primary)
It is a myeloproliferative disorder with low or normal erythropoietin and is a diagnosis of exclusion. With a renal mass, a secondary cause is much more likely.
lightbulb Key takeaway
Work up polycythaemia step by step: rule out relative causes (hydration, protein), then hypoxaemia (SpO₂, blood gas, echocardiography) and, if absent, look for renal lesions and measure erythropoietin. If there are hyperviscosity signs, phlebotomy brings relief while the cause is treated.
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.