How soon should a complete blood count (CBC) be repeated after finding an elevated red blood cell count, hyperhemoglobinemia, and elevated hematocrit?

From the Guidelines

A follow-up CBC should be performed within 1-4 weeks after finding an elevated red blood cell count, hyperhemoglobinemia, and elevated hematocrit, as the current elevations (hemoglobin of 17.5 and hematocrit of 53.9) do not meet the threshold for immediate intervention as outlined in the guidelines 1. The decision to repeat a CBC is influenced by the severity of the abnormalities and the suspected underlying cause. Given the patient's current laboratory values, which are below the threshold for therapeutic phlebotomy (hemoglobin greater than 20 g per dL and hematocrit greater than 65%) as recommended by the ACC/AHA 2008 guidelines 1, a conservative approach can be taken.

Key Considerations

• The patient's symptoms, if any, should be taken into account when deciding the timing of the follow-up CBC. Symptoms such as headaches, dizziness, or visual disturbances could indicate hyperviscosity and may warrant earlier retesting.
• The patient's medical history, including smoking status, cardiopulmonary disease, or high altitude exposure, should be considered as these factors can influence the interpretation of the CBC results and the urgency of follow-up.
• If polycythemia vera or another myeloproliferative disorder is suspected based on the initial CBC results, additional testing such as JAK2 mutation analysis should be performed before initiating treatment, as suggested by the NCCN guidelines 1.

Follow-Up Interval

The follow-up interval may be shortened if the patient develops symptoms or if there are concerns about the underlying cause of the elevated red blood cell count, hyperhemoglobinemia, and elevated hematocrit. However, for mild to moderate elevations without symptoms, a follow-up CBC within 1-4 weeks is generally appropriate, balancing the need for monitoring with the time required for interventions to take effect.

From the Research

Elevated Red Blood Cell Count and Hyperhemoglobinemia

• The patient's CBC results show an elevated red blood cell count, hyperhemoglobinemia (hemoglobin of 17.5), and elevated hematocrit (53.9) 2, 3.
• These results may indicate polycythemia vera (PV), a myeloproliferative neoplasm characterized by an increased red blood cell mass and increased risk of thrombosis 2.
• The diagnosis of PV is typically made based on the presence of erythrocytosis (hemoglobin >16.5 mg/dL in men or >16.0 mg/dL in women), along with other diagnostic criteria such as the presence of a JAK2 gene variant 2, 3.

Repeat CBC Testing

• There is no specific guideline on how soon to repeat a CBC after finding an elevated red blood cell count, hyperhemoglobinemia, and elevated hematocrit 2, 3, 4.
• However, it is recommended that patients with PV receive regular monitoring of their blood counts, including CBC, to assess their response to treatment and to detect any potential complications 2, 3.
• The frequency of repeat CBC testing may depend on the individual patient's risk factors, symptoms, and treatment plan, and should be determined by a healthcare provider 2, 3.

Treatment and Management

• Patients with PV should receive therapeutic phlebotomy to maintain a hematocrit of less than 45%, as well as low-dose aspirin to reduce the risk of thrombosis 2, 3.
• Cytoreductive therapies, such as hydroxyurea or interferon, may be recommended for patients at high risk of thrombosis or with persistent symptoms 2, 3.
• Regular monitoring of blood counts and other health parameters is essential to ensure effective management of PV and to prevent potential complications 2, 3.