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
How would you describe the CBC?
Click for AnswerThe 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.