The following is the patient’s complete blood count (CBC) from the day you see him:

WBC (109/L)Hb (g/dL)Hct (%)MCV (fL)PLT (109/L)

What’s what: WBC, white blood cell count; Hb, hemoglobin; MCV, mean cell volume; MCHC, mean cellular hemoglobin concentration; RDW-SD, red cell distribution width-standard deviation; platelets, PLT; Normal values: WBC 5-10 x 109/L, RBC 4-6 x 1012/L, Hb 12-16 g/dL, Hct 35-47%, MCV 80-100 fL, MCHC 32-36 g/dL, RDW-SD < 45 fL, platelets (PLT) 150-450 x 109/L

The white cell differential is normal.

The peripheral smear is normal.

Let’s return to the table of diagnostic possibilities and consider what other labs we might want to order:

Apparent polycythemiaUrea and creatinine (prerenal changes)
Primary Low serum erythropoietin
CongenitalMutational analysis
Polycythemia veraJak2 V617F
AcquiredHigh serum erythropoietin
Pulmonary diseaseOxygen saturation, chest X-ray
Heart diseaseEchocardiogram
Sleep apneaSleep study
AndrogensTestosterone level
EPO-producing tumorsLiver function tests, urea and creatinine, uranalysis, imaging studies
Renal disordersUrea and creatinine, uranalysis, imaging studies

The following studies were normal:

  • BUN and creatinine
  • Liver function tests
  • Oxygen saturation on room air
  • Chest X-ray

Here is the result for serum erythropoietin:

Although one might argue against checking for Jak2 V617F in this patient, the test was ordered and the result came back (perhaps unsurprisingly) negative:

When you see him, his Hct is 57.1. The last CBC on record is from 8 years prior when his Hct was 48. He started testosterone about 18 months prior to you seeing him.

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