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Hematocrit (Calculated from Red Blood Cell Volume Fraction)

Published: August 9, 2026Updated: August 17, 2026

This test measures the proportion of red blood cells in your blood, calculated from your red blood cell count and volume. It helps assess red blood cell health and potential blood disorders.

Quick summary

["Your red blood cell volume helps diagnose anemia or polycythemia."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 17, 2026Editorial policy

Key facts at a glance

LOINC
20570-8
Short code
Hct VFr Bld Calc
Synonyms
Hct VFr Bld Calc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
36
Ref high
50
Critical range
18 N/A – 60 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
calculated
CPT
85014
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

Why Is This Test Done?

Doctors may order this test to evaluate conditions affecting red blood cells, such as anemia (low red blood cell count), dehydration, or blood disorders like polycythemia vera. It can also guide treatment decisions for conditions like heart disease or kidney problems.

What Does the Result Mean?

While exact reference ranges vary by lab, a lower hematocrit may suggest anemia or fluid loss, while a higher level could indicate conditions like severe dehydration or polycythemia. Your healthcare provider will interpret results in the context of your overall health.

How Is This Test Performed?

A small blood sample is drawn from a vein in your arm. The test measures red blood cell volume and calculates hematocrit using standard laboratory methods. No special preparation is needed, but fasting may be advised for certain related tests.

What Are Common Causes?

Low hematocrit can result from anemia (e.g., iron deficiency, vitamin B12 deficiency), chronic diseases, or blood loss. High hematocrit may occur with dehydration, high-altitude living, or certain blood disorders like polycythemia.

Reference range

Adult males: 38-50%; Females: 36-44%N/A

Specimen: serum

No special preparation usually required. Stay well hydrated. Inform your healthcare provider of all medications and supplements you are taking.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Clinical Significance

Short name

Hct Calculation

Frequently asked questions

What factors might affect my results?
Several factors can influence hematocrit levels, including recent blood loss, hydration status, medications (e.g., diuretics), or underlying health conditions like heart or kidney disease. Smoking or high-altitude living may also impact results.
Can I adjust my diet to improve my hematocrit?
Yes, if your low hematocrit is due to anemia, eating iron-rich foods (e.g., lean meats, spinach) or vitamin C (to aid iron absorption) may help. Always follow your doctor’s advice for dietary changes, especially if you have a diagnosed condition.
Will I need follow-up tests if my hematocrit is abnormal?
If your hematocrit is outside normal ranges, your doctor may recommend additional tests (e.g., complete blood count, iron studies) or further evaluation of your symptoms to determine the underlying cause and guide treatment.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 17, 2026. · Read our editorial policy