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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 the volume fraction of red cells. It helps assess red blood cell concentration and can indicate conditions like anemia or polycythemia.

Quick summary

["Measures red blood cell volume to check for blood disorders or fluid balance issues."]

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

Key facts at a glance

LOINC
30398-2
Short code
Hct VFr CSF Calc
Synonyms
Hct VFr CSF Calc
Category
chemistry
Sample
csf
Container
Sterile tube
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
1-2 mL
Stability
Immediate analysis required, Refrigerated: 1h
Hemolysis max
200
TAT
4–24 hours
Order
routine

Why This Test Matters in Your Care

Hematocrit is a key part of your complete blood count (CBC). It reflects how much of your blood is made up of red blood cells, which carry oxygen to your body. Low levels may suggest anemia or fluid loss, while high levels could indicate dehydration or blood disorders.

How the Test Works

Your blood sample is analyzed to determine the volume of red blood cells relative to the total blood volume. This calculation is often derived from measurements like red blood cell count and mean corpuscular volume (MCV).

When You Might Need This Test

Doctors may order this test if you have symptoms like fatigue, shortness of breath, or unusual bleeding. It’s also used during pregnancy, before surgeries, or to monitor chronic conditions like kidney disease or heart failure.

What to Expect Before the Test

No special preparation is needed. You’ll have a small needle inserted into your arm, and a few drops of blood will be drawn into a tube. The process takes just a few minutes, and you can return to your normal activities afterward.

Reference range

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

Specimen: csf

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

Hematocrit (HCT) Calculation

Frequently asked questions

What does a low or high hematocrit mean?
A low hematocrit (below expected levels) may signal anemia, where your body doesn’t have enough red blood cells to carry oxygen effectively. High hematocrit could indicate dehydration, polycythemia (too many red blood cells), or conditions like chronic lung disease.
How often should I get this test?
Your doctor will determine how often you need this test based on your health status, symptoms, and medical history. Regular monitoring may be recommended if you have ongoing conditions like kidney disease, heart problems, or if you’re taking certain medications.
Can I affect my hematocrit levels?
Yes, lifestyle factors like hydration status, diet, and exercise can influence hematocrit. Staying well-hydrated, eating iron-rich foods, and avoiding excessive alcohol can help maintain balanced red blood cell levels.
  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