Blood Health
Hematocrit
What This Marker Tells Us
Measures the percentage of your blood volume that consists of red blood cells, providing a straightforward assessment of blood thickness and oxygen-carrying capacity.
Why It Matters
Reflects the proportion of red blood cells to plasma in your blood. Low hematocrit indicates anemia, meaning too few red blood cells are circulating to adequately oxygenate your tissues, causing fatigue, weakness, and reduced endurance. High hematocrit means blood is thick and viscous, increasing risk for blood clots, stroke, and heart attack because blood flows less easily through vessels. Hematocrit correlates directly with hemoglobin and RBC count, providing confirmatory information about oxygen-carrying capacity. Athletes at altitude develop higher hematocrit as an adaptive response to lower oxygen availability. Hematocrit is also affected by hydration status; dehydration concentrates blood and elevates hematocrit while overhydration dilutes it.
How to Interpret Your Trends
Normal hematocrit is approximately 38.3-48.6% for men and 35.5-44.9% for women, with men having higher values due to testosterone effects. Hematocrit below 36% in women or 41% in men indicates anemia requiring investigation. Low hematocrit produces symptoms proportional to severity; mild anemia causes subtle fatigue, while severe anemia dramatically impairs function. Hematocrit above 50% in women or 54% in men may indicate polycythemia, dehydration, or chronic hypoxia. Very high hematocrit (above 55-60%) increases blood viscosity and clotting risk. Optimal hematocrit for athletic performance is typically in the upper normal range without exceeding safety limits.
What Influences This Marker
Hematocrit decreases with anemia from any cause (iron, B12, folate deficiency, blood loss, chronic disease), overhydration, pregnancy (blood volume expansion), and bone marrow disorders. Hematocrit increases with dehydration (concentrated blood), smoking, chronic hypoxia (altitude, lung disease, sleep apnea), testosterone therapy, erythropoietin use, and polycythemia vera. Acute changes often reflect hydration status; testing when dehydrated can falsely elevate hematocrit. Living or training at altitude naturally raises hematocrit over weeks to months.
How Your Team Uses It
Your coach ensures you're well-hydrated, especially around blood testing (dehydration can falsely elevate hematocrit), and implements nutrition strategies supporting healthy RBC production when levels are low.
Related Signals We Also Review
Hemoglobin, RBC count, MCV, ferritin, iron saturation, B12, folate, and hydration status for complete blood and oxygen-carrying capacity assessment.