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 polycythemia||Urea and creatinine (prerenal changes)|
|Primary||Low serum erythropoietin|
|Polycythemia vera||Jak2 V617F|
|Acquired||High serum erythropoietin|
|Pulmonary disease||Oxygen saturation, chest X-ray|
|Sleep apnea||Sleep study|
|EPO-producing tumors||Liver function tests, urea and creatinine, uranalysis, imaging studies|
|Renal disorders||Urea 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.