Hematocrit is the percentage volume of red blood cells compared to your total blood volume. Red blood cells carry oxygen to the body to help power biological functions. More oxygen means improved cognition and increased endurance.

What is Hematocrit?

Hematocrit (also called HCT, packed cell volume, or PCV) is measured by routine lab tests. It is the percentage of red blood cells in your blood or, in other words, the volume of red blood cells divided by the total blood volume [1, 2, 3].

Red blood cells come from the bone marrow, where they differentiate from (are made from) stem cells. The body makes about 2 million red blood cells every second. Every red blood cell lives about 120 days and then eventually ages, dies, and is broken apart by the spleen [4].

Red blood cells carry oxygen, so an increase in hematocrit also increases the ability of the blood to carry oxygen. However, higher hematocrit also increases the thickness (viscosity) of blood, reducing its ability to flow through small blood vessels and reach the tissues in the body. Therefore, higher hematocrit isn’t always better for your health [5].

Hematocrit affects a variety of processes, from throwing off the accuracy of blood sugar measurements to controlling the behavior of platelets and blood clotting proteins [6, 7, 8].

Based on a hematocrit measurement, it is possible to calculate other values that are used to predict, estimate, or evaluate [9, 10, 11, 12, 13, 14, 15, 16]:

  • Disease risk
  • Disease severity
  • Surgery-related risks
  • Blood viscosity (which is related to blood flow)
  • Blood loss
  • Rate of treatment (e.g., a dose) needed

Test results vary based on a number of factors, ranging from what kind of device is used to take the measurement to whether you have been drinking enough fluids [17, 2].

Dehydration is a common cause of high hematocrit results [2].

Sitting up (as opposed to lying down) during a blood draw can also increase your results [18].

Normal Values

Normal hematocrit ranges are 40 to 54% for men, 36 to 48% for women, and 30 to 43% for children [2].

However, typical hematocrit can vary between populations depending on both genetic and environmental factors as well as the different measurement techniques used [19].

Hematocrit can vary from day to day or on a more long-term basis depending on altitude, season, athletic training, diet, and pregnancy, among other factors [20, 21, 22, 23, 24].

Hematocrit is a useful diagnostic tool because it can change in generally predictable ways with a health problem [25].


In polycythemia, your blood contains a higher-than-normal proportion of red blood cells. Polycythemia can be “primary,” meaning that there is a problem with the way that your body is making red blood cells, or “secondary,” meaning that the problem is an adjustment to some other influence. For example, your body may be making more red blood cells because it’s not getting enough oxygen [26].

Symptoms of polycythemia can include:

  • Blurred vision
  • Bruising
  • Dizziness
  • Fatigue
  • Headaches
  • Joint pain
  • Stomach pain
  • Weakness

High hematocrit can increase eye pressure, PO2 (the amount of oxygen in your blood), muscle oxygenation, and hand grip strength [27, 28, 29, 30].

High hematocrit can reduce the rate of clearance of a drug from your body and slow down blood flow [31, 32].

High hematocrit can be seen in:

Capillary leak syndrome (leaky blood vessels) [33]

  • Congenital adrenal hyperplasia (misregulated steroid hormones) [34]
  • Cystic fibrosis [35]
  • Dengue fever [36]
  • Ebola [37]
  • Eclampsia (pregnancy complications) [38]
  • Erythrocytosis (high red blood cells) [39]
  • Heart disease
  • Hypertension (high blood pressure) [40]
  • Hyponatremia (low blood sodium) [41]
  • Hypoxia (low oxygen) [42, 43]
  • Insulin resistance [44]
  • Metabolic syndrome [45]
  • Mountain sickness (at high altitudes) [46]
  • Non-alcoholic fatty liver disease [47]
  • Necrotizing pancreatitis (e.g., from alcohol abuse) [48, 49]
  • Sleep apnea (breathing pauses during sleep) [50]
  • Ovarian hyperstimulation syndrome (e.g., from fertility treatments) [51]
  • Kidney disease [52]
  • Polycythemia vera (a blood cancer) [53]
  • Posterior reversible encephalopathy syndrome (e.g., from high blood pressure) [54, 55]
  • Postpartum depression [56]
  • Prediabetes [57]
  • Retinopathy (eye blood vessel damage) [58]
  • Shock [59]
  • Thrombocythemia (high platelets)
  • Thrombosis (blood clot) [60]

When High Levels Are Good

High hematocrit has a number of health benefits. It can:

  • Increase cognitive function [61]
  • Improve athletic performance [62]
  • Reduce aging [63]
  • Reduce the risk of ulcers [64]
  • Reduce the risk of cavities [65]
  • Reduce the risk of death from heart failure [66]

When High Levels Are Bad

There are health risks associated with high hematocrit. High hematocrit can increase the risk of:

  • Stroke [67]
  • Heart disease [68]
  • Poor outcomes in amyotrophic lateral sclerosis [69]
  • Poor outcomes in sepsis (inflammatory response to infection) [70]
  • Poor outcomes in gangrene [71]


Low hematocrit, or anemia, can be caused by blood loss, your body making fewer red blood cells, or increased destruction of red blood cells. Symptoms of anemia can include difficulty breathing, dizziness, headache, cold skin, pale skin, and chest pain [72].

In some cases, anemia can be signaled by pica, a craving for unusual foods or nonfood substances (e.g., ice, crunchy foods, salty foods, clay, dirt) that goes away with iron supplementation [73].

Low hematocrit can be seen in:

  • Alzheimer’s disease [74]
  • Anemia [75]
  • Arthritis
  • Autism spectrum disorder [76]
  • Bipolar disorder [77]
  • Bone marrow disorders
  • Cerebral palsy [78]
  • Cirrhosis (liver disease) [79]
  • Depression [80]
  • Dyspepsia (stomach problems) [81]
  • Dyspnea (breathing problems) [82]
  • Fibromyalgia [83]
  • Growth hormone deficiency [84]
  • Hematoma (abnormal collection of blood) [85]
  • Hemophilia (a bleeding disorder) [86]
  • HIV [87]
  • Hypotension (low blood pressure) [88]
  • Hypothermia [89]
  • Infection
  • Inflammatory diseases
  • Kidney disease or failure [90]
  • Leukemia
  • Massive blood loss (e.g., from trauma, cancer, internal bleeding)
  • Nutritional deficiency (e.g., low iron, folic acid, vitamin B12) [79]
  • Parasitemia (parasites in the blood, e.g., in malaria) [91]
  • Periodontitis (gum disease) [92]
  • Sepsis (inflammatory response to infection) [93]
  • Shock
  • Sickle cell disease [94]
  • Systemic sclerosis (an autoimmune disease) [95]
  • Thalassemia
  • Type 1 diabetes [96]

When Low Levels Are Good

Low hematocrit has some health benefits. It can [62, 97]:

  • Increase VO2 max (the maximum amount of oxygen you can use during intense exercise)
  • Reduce the risk of seizures

When Low Levels Are Bad

There are health risks associated with low hematocrit. Low hematocrit can increase the length of hospital stay after surgery. It also can increase the risks of [98]:

  • Complications from surgery [99]
  • Surgical site infection [100]
  • Hospital readmission after surgery [101]
  • Need for blood transfusion [102]
  • Tuberculosis [103]
  • Ischemia (restricted blood flow to part of the body) [104]
  • Poor outcome from injury [105, 106]
  • Poor outcome from pneumonia [107]

How to Increase Hematocrit

You may be increasing your hematocrit, or naturally have higher hematocrit, without realizing it. This may be due to:

  • Adjusting to a high altitude [108]
  • Alcohol consumption [109]
  • Being male [110]
  • Being overweight [111]
  • Mental stress [112]
  • Military training [113]
  • Smoking cigarettes [114]
  • Spaceflight [115]
  • Workplace pollution [116, 117]
  • Your sleeping position (head tilted downward) [118]

How to Increase Levels Naturally

You can increase your hematocrit by participating in the following activities:

  • Swimming [119]
  • Aerobic exercise [120]
  • Brisk walking [121]
  • Dance therapy [122]
  • High-intensity interval exercise [123]

You can increase your hematocrit by consuming foods or supplements that increase iron [124]. For example, you can increase your hematocrit by eating or drinking [125, 126, 127]:

  • Almonds
  • Artichokes
  • Beans
  • Chickpeas
  • Dried fruit
  • Fermented foods
  • Fish and shellfish
  • Flaxseed oil
  • Green, leafy vegetables
  • Iron-fortified foods
  • Lentils
  • Millet (shown by an animal study)
  • Molasses
  • Pomegranate juice
  • Prune juice
  • Pumpkin seeds
  • Soybeans or tofu

Because vitamin C helps the body absorb iron, you can increase hematocrit by consuming fruits and vegetables that are rich in vitamin C, such as [124]:

  • Broccoli
  • Brussels sprouts
  • Cabbage
  • Cantaloupe
  • Kiwi
  • Peppers
  • Potatoes
  • Strawberries
  • Tomatoes

In addition, copper helps prevent anemia by helping with iron storage and absorption. You can increase hematocrit by consuming foods that are rich in copper, such as:

  • Cashews
  • Sesame seeds
  • Shiitake mushrooms
  • Sunflower seeds
  • Tempeh
  • Walnuts

Medical Treatments that Increase Levels

Hematocrit can be increased medically with:

Drugs That Increase Levels

Drugs used for treating hypogonadism (inadequate testosterone), organ transplant recipients, anemia, surgical blood loss (reducing blood loss), uterine fibroids, Crohn’s disease, and arthritis can increase hematocrit [133, 134, 135, 136, 137, 138, 139, 140].

Hematocrit can also be increased as a result of taking:

  • Dogmatil [141]
  • Hydroxyurea [142]
  • Polyethylene glycol [143]
  • Sodium-glucose cotransporter 2 inhibitors [144]
  • Steroids [145]
  • Tongkat Ali [146]
  • Tranexamic acid [147]

How to Reduce Hematocrit

You may be reducing your hematocrit without realizing it due to:

  • Being a farmer [148]
  • Being a trained athlete [149]
  • Being pregnant [150]
  • Contaminated drinking water [151]
  • Exposure to allergens [152]
  • Workplace pollution [153]

How to Reduce Hematocrit Naturally

You can reduce your hematocrit [154, 155, 156, 119]:

  • By running a marathon
  • By scuba diving
  • With endurance training
  • With judo

You can reduce your hematocrit by consuming [157, 158]:

  • Bran (interferes with iron absorption)
  • Caffeine
  • Grapefruit
  • Milk

Medical Treatments that Reduce Levels

Hematocrit can be reduced medically by (or as a side-effect of):

  • Anesthesia [131]
  • Blood donation [159]
  • Bloodletting (phlebotomy) [160]
  • Cardiopulmonary bypass (artificial circulation during surgery) [161, 162]
  • Chemotherapy
  • Hemodilution (a blood conservation technique used in surgery) [163]
  • Immunoglobulin treatment [164]
  • Positive airway pressure therapy for sleep apnea [165]
  • Post-traumatic resuscitation [166]
  • Radiation therapy [167]

Drugs That Reduce Levels

Drugs for mountain (altitude) sickness, polycythemia vera (a blood cancer), type 2 diabetes, male contraception, and malaria can reduce hematocrit [168, 169, 170, 171, 172].

Hematocrit can also be reduced as a result of taking:

  • ACE inhibitors (for, e.g., high blood pressure) [173]
  • Aspirin [174]
  • Desmopressin [175]
  • Finasteride [176]
  • Glycerol [177]
  • Ibuprofen [178]
  • Metformin [179]
  • Misoprostol [180]
  • Rivaroxaban [181]
  • Tocolytic agents [182]

Hematocrit Genetics

Hematocrit levels are influenced by your genes.

If you’ve gotten your genes sequenced, SelfDecode can help you determine if your levels are high or low as a result of your genes, and then pinpoint what you can do about it.

If you’re sick and tired of guessing about your health, SelfDecode can help you find specific answers that conventional doctors/diagnostics may never uncover.

ABOrs2073823Hematocrit higher for AA genotype [183]
AKT3rs4590656Hematocrit higher for CT genotype [184]
AQP1rs1049305Hematocrit higher for GG genotype [183]
AQP1rs10244884Hematocrit higher for TT genotype [183]
EPAS1rs6756667Hematocrit higher for GG genotype, compared to AG genotype, during the development of mountain sickness [185]
EPOrs551238Hematocrit higher with G allele [186]
EPOrs1617640Hematocrit higher with G allele [186]
EPOrs62483572Lower hematocrit with D70N mutation [187]
EPORrs121918116Hematocrit higher with A allele [188]
FTO (“Fat Gene”)rs9939609Hematocrit decreases more dramatically for the AA or AT genotype, compared to the TT genotype, with diet and exercise [189]
G6PDrs1050828Lower hematocrit with T allele, compared to A allele, for African Americans [190]
GNB3rs5443Hematocrit higher with T allele [191]





Hematocrit higher with JAK2V617F mutation [192]
ND2rs28357984 (Mt5178)Higher hematocrit with A allele, compared to C allele [193]

Irregular Hematocrit Levels?

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