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Whole Blood Hematocrit (Hematocrit)

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

This test measures the proportion of red blood cells in your blood sample, helping assess your blood’s ability to carry oxygen and detect conditions like anemia or polycythemia.

Quick summary

["Hematocrit reflects red blood cell volume in your blood—critical for diagnosing blood disorders and overall health."]

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

Key facts at a glance

LOINC
102868-7
Short code
Wheat Bran IgG RAST
Synonyms
Wheat Bran IgG RAST
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
10
Ref high
40
Critical range
— – 500 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
rast
CPT
84484
SNOMED
302774002
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

What Is Hematocrit?

Hematocrit is the percentage of red blood cells (RBCs) in your blood, calculated by dividing the volume of RBCs by the total blood volume. It’s part of a complete blood count (CBC) and helps doctors evaluate your blood’s oxygen-carrying capacity and check for conditions like anemia or dehydration.

Why Is It Tested?

Doctors order hematocrit to diagnose or monitor conditions such as anemia (low RBCs), polycythemia (high RBCs), dehydration, or blood disorders. It may also be checked before surgeries or treatments that affect blood volume.

How Is It Done?

A small blood sample is drawn from a vein, typically in your arm. The sample is then analyzed in a lab to measure the volume of red blood cells relative to the total blood volume.

What Does It Tell You?

Results help identify whether your RBC levels are too high or too low. While absolute reference ranges vary by lab, trends (e.g., consistently low or high values) often signal underlying health concerns.

Reference range

Adult: 10-40 U/LN/A

Specimen: serum

No special preparation required. Avoid fatty meals before the test if possible.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Hematocrit

Frequently asked questions

What causes low hematocrit?
Low hematocrit can result from anemia (e.g., iron deficiency), blood loss (e.g., from bleeding), chronic diseases (e.g., kidney disease), or certain medications. It may also occur with overhydration or rapid weight gain.
What causes high hematocrit?
High hematocrit often signals polycythemia (too many RBCs), which can be caused by conditions like lung disease, dehydration, or rare blood disorders. It may also appear with long-term altitude exposure or certain cancers.
When should I ask about follow-up?
If your hematocrit is consistently outside expected ranges (discuss with your doctor), or if you experience symptoms like fatigue, shortness of breath, or unusual bleeding, follow up with your healthcare provider.
  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