Elevated Red Blood Cell (RBC) count and hematocrit with normal hemoglobin

From the Guidelines

Elevated Red Blood Cell (RBC) count and hematocrit with normal hemoglobin is likely due to relative polycythemia, which is caused by a reduction in plasma volume, rather than an actual increase in red blood cell mass 1.

Possible Causes

• Dehydration: a common cause of relative polycythemia, as it reduces plasma volume and concentrates red blood cells 1
• Diuretic use: can lead to dehydration and subsequent relative polycythemia 1
• Other conditions: such as hypertension, heart disease, or liver disease, which can cause changes in plasma volume and lead to relative polycythemia 1

Diagnostic Approach

• Hemoglobin and hematocrit levels: should be evaluated in the context of the patient's overall clinical presentation, as a normal hemoglobin level with elevated hematocrit may indicate relative polycythemia 1
• Red blood cell mass (RCM) measurement: may not be necessary in all cases, as a normal-range RCM reading does not rule out the possibility of polycythemia vera (PV), and an elevated RCM is almost always present in cases with a hematocrit level higher than 60% 1
• Serum erythropoietin (EPO) level: can be useful in distinguishing between primary and secondary polycythemia, as EPO levels are typically low in PV and high in secondary polycythemia 1

Key Points

• Polycythemia vera (PV): a myeloproliferative disorder characterized by an increased red blood cell mass, which may not always be accompanied by an elevated hemoglobin level 1
• JAK2 mutation: a genetic abnormality commonly found in PV, which can be used as a diagnostic criterion 1
• Diagnostic criteria: the 2001 WHO criteria for PV have been revised to include the presence of a JAK2 mutation and other biologically relevant minor criteria 1

From the Research

Elevated Red Blood Cell (RBC) Count and Hematocrit with Normal Hemoglobin

• An elevated RBC count and hematocrit with normal hemoglobin levels can be an indicator of various conditions, including dehydration, polycythemia vera, or other disorders that affect red blood cell production 2.
• A study published in 2008 found that individuals with unconjugated hyperbilirubinemia and Gilbert's syndrome had higher RBC mass, hemoglobin, and hematocrit values compared to control subjects 3.
• The complete blood count (CBC) with differential is a common laboratory test that provides information about the production of all blood cells, including RBCs, and identifies the patient's oxygen-carrying capacity through the evaluation of RBC indices, hemoglobin, and hematocrit 4.
• Another study published in 2020 found that high and low hematocrit and hemoglobin levels are associated with the risk of cardiovascular disease, and that increases in the levels of hematocrit, hemoglobin, and RBCs within normal ranges may have beneficial effects on the vasculature 2.

Possible Causes and Associations

• Elevated RBC count and hematocrit with normal hemoglobin levels can be associated with vascular smooth muscle dysfunction and abnormal vascular structure 2.
• The accuracy and precision of CBC measurements can vary depending on the instrument and type of clinical conditions, and internal quality control of automated multichannel hematology analyzers is recommended 5.
• A study published in 1997 discussed the physiologic basis and clinical usage of the complete blood count, including the function, life cycle, and physiology of the various cell components 6.

Laboratory Tests and Measurements

• The complete blood count is one of the most frequently ordered laboratory tests in medicine, and its components include the RBC count, hemoglobin, hematocrit, and other parameters 4, 6.
• The clinically acceptable levels for blood cell count were reported to be 4% for RBC, 3% for hemoglobin, 4% for MCV, 5% for WBC, and 7% for PLT, by JCCLS in 1994 5.