Hemoglobin Free (Unbound) in Serum or Plasma
This test measures the amount of hemoglobin that is not bound to other substances in your blood, often detected after red blood cell destruction or certain medical conditions.
["Free hemoglobin can signal red blood cell breakdown or other blood-related issues."]
Key facts at a glance
- LOINC
- 16925-0
- Short code
- Haem influ A Ag Ur Ql
- Synonyms
- Haem influ A Ag Ur Ql
- Category
- chemistry
- Sample
- urine
- Container
- Sterile urine container
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Specimen volume
- 10 mL
- Stability
- Room temperature: 2h, Refrigerated: 24h, Frozen: 7d
- Hemolysis max
- 0
- Lipemia max
- 0
- Icterus max
- 0
- TAT
- 4–24 hours
- Order
- routine
What Is Free Hemoglobin?
Hemoglobin is the protein in red blood cells that carries oxygen. Normally, it binds tightly to other molecules, but in some cases, it may exist as free hemoglobin. This test specifically looks for unbound hemoglobin in your bloodstream, which can occur when red blood cells break apart (hemolysis) or during certain medical procedures.
Why Might Your Doctor Order This Test?
Your doctor may request this test if you have symptoms like fatigue, dark urine, or signs of red blood cell damage. It can also be checked during conditions such as hemolytic anemia, kidney disease, or after certain blood transfusions or treatments.
How Is This Test Performed?
A blood sample is drawn from a vein, usually in your arm. The sample is then processed to separate serum or plasma from cells, and the free hemoglobin level is measured using a specialized laboratory method.
What Does a Free Hemoglobin Test Tell You?
Elevated levels may indicate conditions like hemolysis (destruction of red blood cells), kidney problems, or certain medications or toxins affecting red blood cells. Lower levels alone may not be clinically significant unless part of a broader evaluation.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Free hemoglobin is primarily important in diagnosing conditions that cause red blood cell breakdown or when monitoring patients with known hemolytic disorders. It can also help identify complications from blood transfusions or exposure to certain toxins that damage red blood cells.
Short name
Free Hemoglobin (Serum/Plasma)
Frequently asked questions
What causes free hemoglobin to be elevated?
How long does it take to get results?
Can lifestyle changes affect this test?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
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.
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