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Hematocrit represents the percentage of blood that is made up of red blood cells. It affects blood flow, blood pressure, viscosity, and platelet adhesion. Low levels may be due to anemia, chronic disease, blood loss, or nutrient insufficiency. Elevated levels may be associated with dehydration, erythrocytosis, heart disease, testosterone therapy, burns, and insulin resistance.
Under normal circumstances, the value of hematocrit will be three times the value of hemoglobin in mg/dL units. An abnormal hematocrit can compromise blood flow and have wide-ranging effects in the body.
Male 38.5 - 50%
Female 35 - 45%
The ODX Range:
Male 40 - 48%
Female 37 - 44%
Low hematocrit is associated with anemia, blood loss, nutrient deficiency, bone marrow failure, rheumatoid arthritis, cancer, hemoglobinopathy, cirrhosis, kidney disease, hyperthyroidism, and high altitudes. The medications chloramphenicol and penicillin can reduce hematocrit (Pagana 2022).
High hematocrit levels are associated with severe dehydration, erythrocytosis, polycythemia vera, congenital heart disease, COPD, eclampsia, and burns (Pagana 2022). Higher hematocrit has also been associated with increased blood viscosity insulin resistance, risk of diabetes (Irace 2014), cardiovascular risk (Gotoh 2015), and testosterone therapy (Fernández-Balsells 2010).
Hematocrit reflects the proportion or percentage of total blood volume that is made up of RBCs. It has direct effects on cardiac output, venous return, blood viscosity, blood pressure, and platelet adhesion (Paul 2012).
When RBCs are normal size with normal amounts of hemoglobin, the hematocrit value will be approximately three times the hemoglobin concentration. Hematocrit values are affected by the same conditions and pathologies that RBCs and hemoglobin are, including hydration and RBC size and morphology. Extremely high WBC count may also affect hematocrit levels (Pagana 2022).
A prospective cohort study of 49,983 adults demonstrated a U-shaped curve associated with hematocrit and mortality in both men and women. Hematocrit of 40-49% in men and 35-44% in women was associated with the lowest overall mortality even after adjustment for several factors, including age, smoking, body mass index, and history of hypertension, heart disease, diabetes, and cancer (Boffetta 2013).
In those with existing hypertension, the lowest risk of all-cause mortality was associated with a tighter range for a hematocrit of 42-44% in men and 38-42% in women (Paul 2012).
Low hematocrit, like low hemoglobin, is associated with an increased risk of contrast-induced nephropathy. Hematocrit below 36.8% had the greatest risk of hypotension and need for hemodynamic support in patients undergoing percutaneous coronary intervention. The risk was especially pronounced in those with the greatest drop in hematocrit around the time of the procedure. Lower levels of hematocrit were associated with additional risk factors, including hypertension, lower glomerular filtration rate, diabetes, peripheral artery disease, congestive heart failure, and a history of myocardial infarction, stroke, and coronary bypass surgery (Nikolsky 2005).
Boffetta, Paolo et al. “A U-shaped relationship between haematocrit and mortality in a large prospective cohort study.” International journal of epidemiology vol. 42,2 (2013): 601-15. doi:10.1093/ije/dyt013
Fernández-Balsells, M Mercè et al. “Clinical review 1: Adverse effects of testosterone therapy in adult men: a systematic review and meta-analysis.” The Journal of clinical endocrinology and metabolism vol. 95,6 (2010): 2560-75. doi:10.1210/jc.2009-2575
Gotoh, Seiji et al. “Hematocrit and the risk of cardiovascular disease in a Japanese community: The Hisayama Study.” Atherosclerosis vol. 242,1 (2015): 199-204. doi:10.1016/j.atherosclerosis.2015.07.014
Irace, Concetta et al. “Blood viscosity in subjects with normoglycemia and prediabetes.” Diabetes care vol. 37,2 (2014): 488-92. doi:10.2337/dc13-1374
Nikolsky, Eugenia et al. “Low hematocrit predicts contrast-induced nephropathy after percutaneous coronary interventions.” Kidney international vol. 67,2 (2005): 706-13. doi:10.1111/j.1523-1755.2005.67131.x
Pagana, Kathleen Deska, et al. Mosby’s Diagnostic and Laboratory Test Reference. 16th ed., Mosby, 2022.
Paul, Laura et al. “Hematocrit predicts long-term mortality in a nonlinear and sex-specific manner in hypertensive adults.” Hypertension (Dallas, Tex. : 1979) vol. 60,3 (2012): 631-8. doi:10.1161/HYPERTENSIONAHA.112.191510