Which ICD‑10‑CM code should be used for a patient with mildly elevated red blood cell count and hematocrit when no specific cause such as dehydration, high altitude, or a primary myeloproliferative disorder is identified?

ICD-10-CM Code for Mildly Elevated RBC and Hematocrit

Use ICD-10-CM code D75.1 (Secondary polycythemia) when mild elevations of RBC and hematocrit are documented without identified primary myeloproliferative disease, or use R70.1 (Abnormal red blood cell morphology) or R71.8 (Other abnormality of red blood cells) if the clinical picture remains unclear and you're documenting an incidental finding pending workup.

Coding Algorithm

The appropriate ICD-10 code depends critically on whether you've ruled out polycythemia vera (PV) and identified the elevation as truly secondary or reactive:

Step 1: Determine if This is Polycythemia Vera (Primary)

Before coding as a benign finding, you must exclude PV, which has significant mortality implications from thrombosis, hemorrhage, and leukemic transformation 1.

Key distinguishing features of PV to exclude:

• Hemoglobin >16.5 g/dL (men) or >16.0 g/dL (women) with hematocrit >49% (men) or >48% (women) 2
• Presence of JAK2 V617F mutation (found in >95% of PV cases) 3, 1
• Associated leukocytosis (49% of cases) and/or thrombocytosis (53% of cases) 1
• Suppressed serum erythropoietin levels 3, 2
• Clinical features: pruritus, erythromelalgia, splenomegaly, or history of thrombosis 1

If JAK2 is positive or WHO criteria for PV are met: Use D45 (Polycythemia vera) instead.

Step 2: Identify Secondary Causes

If PV is excluded, determine if a secondary cause exists 4:

Common secondary causes requiring D75.1:

• Chronic hypoxia (COPD, sleep apnea, smoking, high altitude residence)
• Medications (androgens, SGLT2 inhibitors, erythropoietin-stimulating agents)
• Renal pathology (renal artery stenosis, cysts, tumors)
• Other EPO-secreting tumors (hepatocellular carcinoma, cerebellar hemangioblastoma)

If a clear secondary cause is identified: Use D75.1 (Secondary polycythemia)

Step 3: Consider Relative Polycythemia

If the elevation is mild and potentially due to plasma volume contraction (dehydration, diuretics, stress):

Use D75.1 for documented relative polycythemia, though some coders prefer E86.0 (Dehydration) if dehydration is the primary issue.

Step 4: Coding Incidental or Unclear Findings

For truly mild, incidental elevations pending workup where you haven't yet determined primary vs. secondary:

• R71.8 (Other abnormality of red blood cells) - Most appropriate for documented abnormal lab values without established diagnosis
• R70.1 (Abnormal red blood cell morphology) - If morphologic changes noted
• D75.9 (Disease of blood and blood-forming organs, unspecified) - Less specific fallback

Critical Clinical Pitfalls

Do not assume altitude or smoking explains erythrocytosis without checking JAK2. Even at high altitude, PV patients have distinct CBC patterns with leukocytosis, thrombocytosis, and microcytic RBCs from iron deficiency 5. The presence of these additional cytopenias should trigger JAK2 testing regardless of altitude 5, 6.

Paradoxically low EPO at altitude is a red flag for PV 6. Normal altitude residents have elevated EPO; suppressed EPO with erythrocytosis suggests autonomous (clonal) proliferation 6.

The TRAKJAK score can help predict which patients need JAK2 testing to reduce unnecessary workup costs 7, but when thrombocytosis or leukocytosis accompanies erythrocytosis, proceed directly to JAK2 testing 4.

Documentation Requirements

For proper coding, your documentation should specify:

• Actual hemoglobin and hematocrit values
• Presence or absence of leukocytosis/thrombocytosis
• JAK2 mutation status (if tested)
• Identified secondary causes (smoking history, altitude, medications, comorbidities)
• Whether this represents new finding vs. chronic stable condition

Without adequate workup documented, use R71.8 rather than D75.1, as secondary polycythemia implies you've excluded primary disease and identified a cause.