Hematocrit

The reference range varies depending on the methodology used. Normal ranges should be validated by individual clinical laboratories.

Reference ranges (SI units/conventional units) are as follows:

• Males - 0.40-0.54/40-54%

• Females - 0.36-0.46/36-46%

• Newborns - 0.53-0.69/53-69%

Causes of decreased hematocrit include, but are not limited to:

• Anemia (eg, iron deficiency anemia, aplastic anemia, lead poisoning, thalassemia)

• Bleeding (eg, acute blood loss from trauma [may be normal initially], GI bleeding) ^[1]

• Red blood cell destruction (eg, autoimmune hemolytic processes, drug-induced hemolytic anemia, TTP, sickle cell disease, splenomegaly)

• Bone marrow suppression or underproduction (eg, leukemia, myelodysplasia, chemotherapy)

• Malnutrition and nutritional deficiencies (eg, folate deficiency, vitamin B12 deficiency, Kwashiorkor)

• Infection (eg, parvovirus, sepsis)

• Overhydration (eg, polydipsia)

• Pregnancy ^[2]

Causes of increased hematocrit include, but are not limited to:

• Dehydration (eg, from fluid suppression or heat stroke) ^[3]

• Congenital heart disease

• Cor pulmonale (eg, sleep apnea, COPD) ^[4]

• Erythrocytosis (eg, primary or secondary polycythemia vera)

• Hypoxia in low-oxygen states (eg, high altitude, premature babies with delayed lung development)

Specimen: whole blood

Collection: ethylenediaminetetraacetic acid (EDTA) tube, purple/lavender or pink top (see image below)

Full blood count Vacutainer.

Panels: complete blood count

Description

Hematocrit is the fraction of whole blood composed of red blood cells. Hematocrit rises with an increase in the number of red blood cells or a decrease in the plasma volume. Conversely, hematocrit decreases when plasma volume increases or in states of decreased erythropoiesis or increased red cell destruction or loss. Hematocrit may be measured directly by centrifugation or indirectly by automated methods. ^[5]

Indications/Applications

Hematocrit may indicate that a patient has anemia, erythrocytosis, or changes in plasma volume. Hematocrit may be used as a cutoff to determine transfusion requirements. Following hematocrit as a marker over time may help to determine response to treatment.

Considerations

Increased spurious results may be seen by centrifugation methods when plasma trapping or hyponatremia exists, ^[6] or by automated methods when hyperglycemia, high white blood cell counts, giant platelets, or cryoglobulins are present. Decreased spurious results may be seen by centrifugation methods when excess EDTA, hypernatremia, or in vitro hemolysis is present, or by automated methods when clotting, agglutination, hemolysis, or RBC microcytosis is evident.

Hematocrit may be decreased in pregnancy secondary to increased plasma volumes.

Reference ranges for populations residing in high-altitude areas may be increased secondary to increased oxygen carrying capacities at higher elevations.

A study by Hinzmann et al indicated that, according to real-world data, systems for self-monitoring of blood glucose that have been specified for performance only within the 30-55% hematocrit range are at risk of producing erroneous results for 3% of outpatients in Europe and 18% of those in South Africa. This is because those percentages of these outpatient populations have hematocrits outside that range. ^[7]