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Differential Diagnosis: Erythrocytosis

Julie Allen, BVMS, MS, MRCVS, DACVIM (SAIM), DACVP (Clinical), Durham, North Carolina

Internal Medicine

|November/December 2020|Peer Reviewed|Web-Exclusive

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Differential Diagnosis: Erythrocytosis

Following are differential diagnoses for patients presented with erythrocytosis.

  • Absolute erythrocytosis (ie, increased RBC mass)
    • Breed-related erythrocytosis (eg, sight hounds [eg, greyhounds], dachshunds)
    • Primary erythrocytosis (ie, polycythemia vera)
    • Secondary erythrocytosis
  • Appropriate (response to systemic hypoxia or increased hemoglobin affinity) 
    • Carbon monoxide poisoning 
    • Congenital heart defect involving right-to-left shunting (eg, ventricular septal defect with Eisenmenger’s syndrome, tetralogy of Fallot, reverse patent ductus arteriosus)
    • High altitude
    • Respiratory disease (eg, brachycephalic obstructive airway syndrome, chronic pulmonary disease)
    • Severe obesity
  • Inappropriate (absence of systemic hypoxia)
    • Acromegaly
    • Erythropoietin-producing tumors (eg, splenic hemangiosarcoma, cecal leiomyosarcoma, hepatic tumors)
    • Hyperadrenocorticism
    • Hyperthyroidism
    • Local renal hypoxia (eg, pyelonephritis, leptospirosis, renal tumors [eg, carcinoma, sarcoma, lymphoma])
  • Relative erythrocytosis (common)
    • Dehydration
    • Splenic contraction (eg, with exercise, fear, or excitement)


For global readers, a calculator to convert laboratory values, dosages, and other measurements to SI units can be found here.

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