Skip to content

Hemoglobin Free Hemoglobin (Serum)

Published: August 9, 2026Updated: August 16, 2026

This test measures the amount of free hemoglobin in your blood serum, which is not bound to red blood cells. Free hemoglobin can indicate conditions like hemolysis (destruction of red blood cells) or certain medical treatments.

Quick summary

["Free hemoglobin levels may signal red blood cell breakdown or other blood-related conditions."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
43429-0
Short code
Haem influ B Ag Ser Ql
Synonyms
Haem influ B Ag Ser Ql
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
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 This Test Might Be Ordered

Your healthcare provider may order this test if you have symptoms like fatigue, dark urine, or signs of anemia. It could also be used to monitor conditions such as hemolytic anemia, blood transfusions, or certain medications that affect red blood cells.

What to Expect Before the Test

No special preparation is typically needed. You may have a small needle inserted into your arm to draw blood. If you’re on blood-thinning medications or have a history of bleeding disorders, let your provider know.

What the Results Mean

Free hemoglobin levels outside of normal ranges may suggest red blood cell destruction or other blood abnormalities. Your provider will interpret results in the context of your overall health and symptoms.

Common Conditions Monitored

This test helps diagnose or monitor conditions like hemolytic anemia, intravascular hemolysis (where red blood cells break apart inside blood vessels), or assess the effectiveness of treatments like blood transfusions or certain drugs.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Free Hemoglobin

Frequently asked questions

What causes free hemoglobin to rise?
Free hemoglobin can increase due to hemolysis (e.g., from autoimmune disorders, infections, or certain medications), blood transfusions, or conditions like sickle cell disease.
How is this test different from a regular hemoglobin test?
A regular hemoglobin test measures total hemoglobin in red blood cells, while this test specifically looks at free hemoglobin, which is not bound to cells. Free hemoglobin can be detected even if total hemoglobin is normal.
Can diet affect this test?
Dietary factors generally do not directly affect free hemoglobin levels, but they can influence overall red blood cell health. If you’re on medications, always follow your provider’s instructions.
  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 16, 2026. · Read our editorial policy