Hematocrit (Hct)
Hematocrit represents the volumetric percentage of whole blood composed of packed red blood cells, directly governing systemic blood viscosity and shear stress.
Standard vs. Optimal Reference Ranges%
Standard reference intervals represent the statistical 95% distribution of unselected commercial populations. Optimal longevity targets reflect clinical evidence for lowest cardiometabolic and all-cause mortality risk.
Analyte is within optimal non-reactive clinical parameters.
41% - 50% (Male), 36% - 48% (Female)
General reference distribution across unselected commercial populations.
42% - 47% (Male), 38% - 44% (Female)
Concentration target associated with minimal all-cause cardiometabolic mortality.
Molecular Mechanism & Clinical Purpose
Calculated as [RBC count × MCV] / 10. Governed by plasma volume regulation (ADH/aldosterone) and total erythron mass.
Differential Diagnosis
Elevated Levels (Hct High)
- •Dehydration / Intravascular volume contraction
- •Chronic obstructive pulmonary disease / Obstructive sleep apnea
- •Testosterone replacement therapy (TRT erythrocytosis)
Low Levels (Hct Low)
- •Anemia of any etiology
- •Acute plasma volume expansion / Overhydration
- •Chronic hemorrhage
Technical Reference & Deep Dive
Biochemistry & Enzymatic Pathways
Longevity Risk Architecture & Epidemiology
Pre-Analytical Caveats & Diagnostic Workup
Pre-Analytical Considerations:
Fasting is not strictly required for standard Complete Blood Count, but consistent morning timing is advised due to circadian fluctuations in leukocyte counts. Venipuncture must be performed with minimal stasis in K2-EDTA tubes and gently inverted 8 to 10 times to prevent microclots. Dehydration causes hemoconcentration and spuriously elevates cellular counts; ensure normal fluid intake before testing.
Reflexive Testing Protocol:
- Peripheral Blood Smear with manual microscopic review to evaluate cellular morphology, poikilocytosis, and blast cells
- Reticulocyte Count and Reticulocyte Hemoglobin Equivalent (Ret-He) to assess dynamic bone marrow erythropoietic response
- Complete Iron Panel (Ferritin, Serum Iron, TIBC, Transferrin Saturation) and Soluble Transferrin Receptor
- Serum Methylmalonic Acid and Homocysteine to screen for functional Vitamin B12 and Folate deficiencies
- Hemoglobin Electrophoresis or High-Performance Liquid Chromatography (HPLC) if hemoglobinopathy or thalassemia is suspected
Clinical Citations & Primary Literature (1)
- [1]Blood Viscosity, Hematocrit, and Vascular Health in Longevity - Circulation (2021). PMID: 33878219
Associated Longevity Guides & Clinical Calculators
Medicine 3.0Explore comprehensive evidence-based clinical protocols, testing costs, and algorithmic calculators that incorporate Hematocrit (Hct) into overall healthspan optimization.