The clinical and laboratory evaluation of the patient with erythrocytosis

•Nearly one-half of patients with erythrocytosis have an underlying non-hematologic etiology.•Practicing internists can diagnose and manage cardio-pulmonary disorders that cause erythrocytosis.•Recognizing clinical features of polycythemia vera and diagnostic value of JAK2 mutation testing are important.•Scientific advances have elucidated the pathogenesis of polycythemia vera, leading to novel treatments.•Congenital erythrocytosis syndromes exhibit diverse molecular pathogenesis.

Erythrocytosis is frequently encountered as an incidental abnormality on laboratory testing that reveals persistent elevation of the hematocrit level (> 52% in men and > 48% in women). In many cases, erythrocytosis is the manifestation of an underlying cardiopulmonary process, drug-induced due to androgens, or secondary to smoking, rather than a primary bone marrow disorder such as polycythemia vera. A systematic approach to the clinical and laboratory evaluation of each patient is indicated to consider diverse differential diagnosis possibilities and to identify the underlying etiology of erythrocytosis in order to formulate appropriate subspecialist referral and management plans. A thorough medical history and meticulous physical examination supplemented by a focused initial laboratory evaluation will enable the general practitioner to ascertain the etiology of erythrocytosis in the majority of cases. Patients with clinical and laboratory features suggestive of polycythemia vera and those patients without an apparent underlying condition known to cause erythrocytosis benefit from early referral to a hematologist for further specialized diagnostic evaluation and therapy considerations.