Is a hemoglobin (Hb) level of 17.2 and hematocrit (Hct) of 50.8 considered polycythemia?

Evaluation of Hemoglobin 17.2 g/dL and Hematocrit 50.8% for Polycythemia

Yes, a hemoglobin of 17.2 g/dL and hematocrit of 50.8% meets the diagnostic criteria for erythrocytosis/polycythemia according to current guidelines. 1

Diagnostic Thresholds

According to the most recent guidelines:

• Erythrocytosis is defined as a hematocrit level >51% or hemoglobin level >17 g/dL (170 g/L) 2
• The 2016 WHO classification for polycythemia vera uses the following hemoglobin thresholds 1:
  • Men: >16.5 g/dL
  • Women: >16 g/dL

The provided values (Hb 17.2 g/dL, Hct 50.8%) exceed the hemoglobin threshold for polycythemia, while the hematocrit is just below the strict cutoff of 51%.

Diagnostic Algorithm

1. Confirm true polycythemia:

   • Rule out relative polycythemia (plasma volume contraction) 3
   • Consider measuring red cell mass if available 3

2. Differentiate primary vs. secondary polycythemia:

   • Order serum erythropoietin (EPO) level 1
     • Low EPO suggests primary polycythemia (PV)
     • Normal/elevated EPO suggests secondary causes

3. If primary polycythemia is suspected:

   • Test for JAK2 V617F mutation (>95% sensitivity for PV) 1
   • If JAK2 V617F negative but strong suspicion remains, test for JAK2 exon 12 mutation 1
   • Consider bone marrow biopsy to assess for hypercellularity with trilineage growth 1

4. If secondary polycythemia is suspected, evaluate for:

   • Hypoxia-driven causes: COPD, sleep apnea, high altitude, smoking, heart disease 1
   • Non-hypoxia driven causes: Renal tumors, hepatocellular carcinoma, exogenous EPO, androgens 1, 3

Important Considerations

• The 2016 WHO classification lowered hemoglobin thresholds for PV diagnosis, which may lead to increased testing in the general population 4
• Some patients may have "masked PV" with normal hemoglobin/hematocrit due to coincidental blood loss or hemodilution 5
• Thromboembolic events are the most lethal complications of PV and often the initial manifestation 6
• In ADPKD patients, erythrocytosis may occur due to regional hypoxia driving production of hypoxia-inducible transcription factors 2

Management Principles

If polycythemia vera is confirmed:

• Target hematocrit <45% to reduce thrombotic events 1
• Therapeutic phlebotomy as first-line therapy 1
• Low-dose aspirin (81-100 mg daily) unless contraindicated 1
• Consider cytoreductive therapy for high-risk patients (age >60 years OR history of thrombosis) 1

For secondary erythrocytosis:

• Treat underlying cause
• In ADPKD-related erythrocytosis, ACE inhibitors or ARBs may be beneficial 2, 1
• Therapeutic phlebotomy if symptomatic hyperviscosity is present 1

Pitfalls to Avoid

• Don't assume polycythemia vera without excluding secondary causes
• Don't overlook the possibility of masked PV in patients with thrombosis and normal blood counts 5
• Avoid aggressive phlebotomy in certain conditions (e.g., cyanotic heart disease) due to risk of iron depletion 1
• Don't forget to evaluate for thrombotic risk factors in all patients with polycythemia