hemoglobinhematocrit

Hemoglobin and hematocrit are two fundamental measurements obtained in a complete blood count. Hemoglobin (Hb) is the iron-containing protein inside red blood cells that binds oxygen in the lungs and releases it to tissues, while also helping transport carbon dioxide back to the lungs for elimination. Hematocrit (Hct) is the proportion of blood volume occupied by red blood cells, expressed as a percentage. Hb is reported in grams per deciliter (g/dL) and Hct as a percentage.

Normal ranges vary by sex and age and may be influenced by altitude and pregnancy. Typical adult reference ranges approximate Hb: men 13.8–17.2 g/dL and women 12.1–15.1 g/dL; Hct: men 40–54% and women 36–44%. In many laboratories, Hb and Hct are reported together as part of a CBC. Values outside the reference ranges can indicate medical conditions that may require further evaluation.

Clinical interpretation: lower Hb and Hct indicate anemia; higher values suggest polycythemia or relative dehydration, among other causes. They are used to diagnose conditions, monitor therapy, and assess oxygen-carrying capacity. The two measures usually track together, but can diverge in certain disorders (for example, abnormal red cell morphology, hydration status, or recent transfusion). The Hb–Hct relationship is often approximated by Hct (%) ≈ Hb (g/dL) × 3, though this is only a rough guide due to variation in red blood cell size and composition.

Measurement methods: Hb is typically measured via spectrophotometry or cyanmethemoglobin methods; Hct is determined by centrifugation of a blood sample or calculated from red blood cell indices.