Labs

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) |
---|---|---|---|---|
8.6 | 19.1 | 57.1 | 90 | 213 |
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:
Cause | Labs |
---|---|
Apparent polycythemia | Urea and creatinine (prerenal changes) |
Primary | Low serum erythropoietin |
Congenital | Mutational analysis |
Polycythemia vera | Jak2 V617F |
Acquired | High serum erythropoietin |
Pulmonary disease | Oxygen saturation, chest X-ray |
Heart disease | Echocardiogram |
Sleep apnea | Sleep study |
Androgens | Testosterone level |
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.