Hematocrit
Blood cell systemAlso known as: HCT, haematocrit, packed cell volume, PCV
Hematocrit measures the percentage of blood volume occupied by cellular components, with the largest portion being red blood cells (erythrocytes).
When blood is centrifuged, blood cells settle at the bottom, creating a visible layer that indicates their proportion relative to total blood volume.
Reference range
Female
Source: lab benchmark
Male
Source: lab benchmark
Reference ranges may vary between labs and assays. Always interpret results with your healthcare provider. · LOINC code: 20570-8
Why this matters
Low hematocrit (anemia) can cause fatigue, weakness, shortness of breath, dizziness, and pale skin due to reduced oxygen delivery to tissues. High hematocrit (polycythemia) can thicken blood, increasing the risk of clots, headaches, and blurred vision. Hematocrit levels are influenced by iron, vitamin B12, folate intake, hydration, and chronic conditions. Monitoring helps detect early red blood cell disorders and supports interventions such as dietary adjustments or further medical evaluation.
How this connects to other biomarkers
- Hematocrit (the percentage of blood volume made up of red cells) moves in parallel with Hemoglobin under most circumstances; major discordance suggests red-cell index abnormalities or measurement artifact.
- Elevated Hct with normal Hgb may simply reflect dehydration; persistent elevation alongside an Hgb increase suggests true polycythemia (the body making too many red cells — primary, or secondary to low oxygen or EPO excess).
- Low Hct with low Hgb and small red cells (low MCV) supports iron-deficiency anemia; with large red cells (high MCV) supports B12 or folate deficiency.
How often should I test Hematocrit?
Most adults benefit from yearly hematocrit testing as part of a complete blood count. After iron supplementation or other anemia treatment, retest at 4 to 8 weeks to confirm response.
At baseline / for screening: Once every 12 months from age 30 as part of a comprehensive panel.
When monitoring an intervention or change: Retest 4 to 8 weeks after starting iron, B12, or folate supplementation for anemia, or after blood loss recovery. Red blood cells take about 120 days to fully turn over, so meaningful changes in cell size and content (MCV, MCH) take 3 to 4 months. Hydration on the morning of the draw shifts concentration-based measures, so reproduce conditions for reliable trends.
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