Is a hemoglobin (Hb) level of 17.6 g/dL indicative of polycythemia in an adult male?

Is Hemoglobin 17.6 g/dL Considered Polycythemia in an Adult Male?

A hemoglobin of 17.6 g/dL in an adult male does NOT meet the diagnostic threshold for polycythemia vera according to WHO criteria, which requires Hb ≥18.5 g/dL, but it does warrant clinical evaluation as it falls in the upper range of normal and may represent early or masked disease. 1

Understanding the Diagnostic Thresholds

WHO Criteria for Polycythemia Vera

The revised 2007 WHO diagnostic criteria establish clear hemoglobin thresholds for polycythemia vera 1:

• Men: Hb ≥18.5 g/dL (or Hb >17 g/dL if associated with a documented and sustained increase of at least 2 g/dL from baseline that cannot be attributed to iron deficiency correction) 1
• Women: Hb ≥16.5 g/dL (or Hb >15 g/dL with sustained increase) 1

Your patient's Hb of 17.6 g/dL falls below the primary diagnostic threshold of 18.5 g/dL. 1

Normal Reference Ranges

According to population-based data, the normal hemoglobin range for adult males extends up to approximately 17.0 g/dL at the 97.5th percentile. 1 A value of 17.6 g/dL represents an elevated but not definitively pathological level in isolation. 2

Clinical Context Matters

When to Pursue Further Workup

You should investigate further if any of the following are present 1, 3:

• Documented sustained increase of ≥2 g/dL from the patient's previous baseline hemoglobin 1
• Clinical features suggestive of myeloproliferative neoplasm: splenomegaly, thrombotic events (especially unusual sites like portal vein), pruritus after bathing, erythromelalgia 3, 4
• Elevated hematocrit: >49% in men (some guidelines use >52%) 4
• Elevated platelet count or leukocytosis 4
• History of unexplained thrombosis, even with normal blood counts 3

The Concept of "Masked" Polycythemia Vera

Approximately 15-35% of polycythemia vera patients present with hemoglobin levels below the WHO diagnostic threshold—termed "masked PV." 4 These patients may have:

• Concurrent iron deficiency masking the true red cell mass elevation 1
• Plasma volume expansion diluting the hemoglobin concentration 3
• Recent blood loss 3

Masked PV patients have worse overall survival compared to overt PV, particularly when age >65 years or WBC >15×10⁹/L. 4

Recommended Diagnostic Approach for Hb 17.6 g/dL

Step 1: Assess for Secondary Causes

Before considering polycythemia vera, exclude secondary polycythemia 5:

• Hypoxia: Check oxygen saturation, consider sleep apnea, chronic lung disease 6
• Smoking history: Increases Hb by 0.3-1.0 g/dL 7
• Altitude: Adjust expected values (add 0.9 g/dL per 1,000 meters elevation) 1
• Renal pathology: Renal cell carcinoma, renal artery stenosis 5
• Testosterone or erythropoietin use 5

Step 2: Determine if Further Workup is Needed

Proceed with myeloproliferative neoplasm workup if 1, 3, 4:

• Sustained elevation on repeat testing (not a single isolated value)
• Any clinical features of myeloproliferative disease
• Unexplained thrombosis
• Elevated platelet count (>400×10⁹/L) or WBC (>12×10⁹/L)
• Splenomegaly on examination

Step 3: If Pursuing PV Diagnosis

Order the following tests 1:

1. JAK2V617F mutation testing (present in ~95% of PV) 1
2. JAK2 exon 12 mutation if JAK2V617F negative 1
3. Serum erythropoietin level (typically low in PV) 1
4. Iron studies (ferritin, TSAT) to assess for iron deficiency that might mask higher Hb 1
5. Bone marrow biopsy showing hypercellularity with trilineage growth if molecular testing is positive 1

Critical Pitfalls to Avoid

Don't Over-Diagnose Based on Single Value

A study of 248,839 patients with normal CBC results found that 5.99% of men had Hb >16.5 g/dL, and isolated use of hemoglobin thresholds leads to substantial unnecessary testing. 2 Do not initiate extensive workup based solely on a single borderline hemoglobin value without clinical context. 2

Don't Miss Iron-Deficient PV

In routine clinical practice, you should not be prevented from making a working diagnosis of PV in the presence of iron deficiency, even if WHO hemoglobin criteria are not met, when other features are present. 1 However, for research purposes, formal PV diagnosis requires demonstrating WHO criteria after iron replacement. 1

Don't Ignore Thrombotic Risk

Patients with masked PV still carry thrombotic risk and may benefit from aspirin therapy, particularly if JAK2-positive. 3, 4 The presence of JAK2 mutations in patients with unusual site thrombosis (portal vein, hepatic vein) should prompt consideration of underlying myeloproliferative disease even with normal hemoglobin. 3

Bottom Line for Hb 17.6 g/dL

This value alone does not diagnose polycythemia vera. 1 However, if this represents a sustained increase from baseline, or if accompanied by clinical features of myeloproliferative disease or unexplained thrombosis, proceed with JAK2 mutation testing and further evaluation. 1, 3, 4 In the absence of these features and after excluding secondary causes, this can be monitored with repeat testing in 3-6 months. 2