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Haematocrit

Anemia Biomarker

Sample Needed

Collection Type: Blood

Body System

Related System: Anemia

Overview

Haematocrit (Hct) is the proportion of blood volume made up by red blood cells, reported as a percentage. The test measures the packed cell volume after centrifugation and helps assess oxygen-carrying capacity. It is used to detect and monitor anaemia, polycythaemia (erythrocytosis), dehydration and haemorrhage. Symptoms prompting testing include fatigue, pallor, shortness of breath, dizziness, rapid heart rate, easy bruising or unusual bleeding. Normal values differ by age, sex and physiological state: males have higher baseline Hct than females, newborns and infants have different reference ranges, and pregnancy typically causes a relative fall due to plasma expansion.

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Test Preparation

No special preparation is required

Why Do I Need This Test

Included in the Anemia profile.
Test is indicated for symptoms of anaemia or polycythaemia (fatigue, breathlessness, pallor, headaches, thrombotic events), to diagnose or monitor anaemia, blood loss, dehydration, or erythrocytosis.
Low Hct suggests reduced red cell mass (iron deficiency, chronic disease, haemolysis, marrow failure, pregnancy dilution); high Hct may reflect dehydration, smoking, high altitude, or myeloproliferative disorders.
Family history of inherited anaemias or polycythaemia warrants testing.

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Understanding Test Results

Values below the sex-specific lower limits (men <41%, women <36%) indicate anaemia and require investigation.
Mild anaemia is often Hct ~30–40% (may cause fatigue, exertional breathlessness); moderate anaemia ~20–30% (clear functional impairment, tachycardia); severe anaemia <20% (risk of cardiac ischemia, syncope, urgent evaluation).
Elevated Hct above the upper limits (men >53%, women >46%) suggests erythrocytosis or relative haemoconcentration.
Modest increases (up to ~56%) may reflect dehydration, smoking or living at altitude; persistent marked elevation (>60%) raises concern for primary polycythaemia (e.g., polycythaemia vera) and increased thrombotic risk and needs prompt workup.
Acute changes can result from fluid shifts (dehydration lowers plasma raises Hct) or recent bleeding/fluid resuscitation lowering Hct; interpret alongside haemoglobin, red cell indices and clinical context.

Normal Range

Men: 41-53% OR Women: 36-46% OR Children (varies by age): 32-44%

FAQs

Q: What happens if hematocrit is low?

A: Low hematocrit means a reduced proportion of red blood cells, often indicating anemia. It can cause fatigue, weakness, shortness of breath, dizziness and palpitations from lower oxygen delivery. Common causes are bleeding, iron/B12/folate deficiency, chronic disease, or bone marrow disorders. Risks include tissue hypoxia and worsening heart disease. Evaluation with blood tests and targeted treatment is needed.

Q: What does it mean if your hematocrit is too high?

A: A high hematocrit means a larger-than-normal proportion of red blood cells in your blood. Causes include dehydration, smoking, living at high altitude, chronic lung disease, tumors or bone-marrow disorders (e.g., polycythemia vera). It raises blood viscosity, increasing risk of clots, stroke and heart attack. Your clinician may repeat tests, check oxygen and erythropoietin levels, and investigate underlying causes to guide treatment.

Q: What is a normal hematocrit range by age?

A: Normal hematocrit ranges by age: Newborn (cord): 55–65% Infants (0–6 months): 30–45% Children (6 months–12 years): 30–42% Adolescents: males 38–50%, females 35–45% Adults: males 40–52%, females 36–48% Older adults: similar to adult ranges. Reference intervals vary by lab, sex, altitude and clinical context; clinicians interpret results alongside symptoms and other tests.

Q: How to improve hematocrit?

A: To raise low hematocrit: get medical evaluation to identify the cause and treat underlying issues (bleeding, chronic disease). Correct deficiencies with an iron-rich diet plus vitamin C to aid absorption and take oral or IV iron if prescribed; replace B12/folate if deficient. For CKD or severe anemia, erythropoiesis-stimulating agents may be used. Follow prescribed treatment and repeat blood tests.

Q: What organ causes low hematocrit?

A: Low hematocrit usually reflects reduced red blood cell mass. The primary organ responsible is the bone marrow—disease or suppression of marrow lowers red cell production. The kidneys also influence levels by producing erythropoietin; kidney disease reduces EPO and leads to low hematocrit. Other causes include bleeding (especially gastrointestinal), increased hemolysis, or splenic sequestration.

Q: How is low hematocrit treated?

A: Low hematocrit treatment targets the underlying cause: iron deficiency: oral or IV iron and dietary changes; vitamin B12 or folate deficiency: specific vitamin replacement; chronic kidney disease: erythropoiesis-stimulating agents; acute or severe symptomatic anemia: blood transfusion. Manage bleeding sources, adjust offending medications, and monitor hematocrit and symptoms with follow-up testing.