Free Hemoglobin in Plasma (Serum)
This test measures the amount of free hemoglobin (Hb) not bound to red blood cells in your blood plasma or serum. Free hemoglobin can indicate conditions affecting red blood cells or blood breakdown.
["Free hemoglobin in plasma may signal red blood cell disorders or hemolysis."]
Key facts at a glance
- LOINC
- 25433-4
- Short code
- Hgb Free Plas-sCnc
- Synonyms
- Hgb Free Plas-sCnc
- Category
- hematology
- Sample
- plasma
- Container
- Lavender-top (EDTA) or Green-top (Heparin)
- Units
- N/A
- Ref low
- 12
- Ref high
- 17.5
- Critical range
- 7 N/A – 20 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- CPT
- 85018
- SNOMED
- 900000000000003004
- 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 Does This Test Measure?
Free hemoglobin is the portion of hemoglobin that is not attached to red blood cells. Normally, hemoglobin is contained within red blood cells. When red blood cells break down (hemolysis) or are damaged, free hemoglobin can enter the plasma or serum. This test helps identify conditions where red blood cells are being destroyed or released prematurely into the bloodstream.
Why Might This Test Be Ordered?
Your healthcare provider may order this test if you have symptoms like fatigue, pale skin, or signs of anemia, or if you have conditions such as hemolytic anemia, sickle cell disease, or certain blood disorders. It may also be used to monitor treatment for conditions affecting red blood cells.
How Is the Test Performed?
A blood sample is drawn from a vein, typically in your arm. The blood is then processed to separate plasma or serum from red blood cells. The free hemoglobin level is measured using a specialized laboratory technique.
What Are Possible Results?
Results are compared to reference ranges specific to your lab. Elevated levels may suggest hemolysis or other blood-related issues, while lower levels may be less commonly reported in this specific test but could relate to conditions affecting red blood cell integrity.
Reference range
Adult males: 13.5-17.5 g/dL; Females: 12.0-16.0 g/dLN/A
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
Free Hb Plasma
Frequently asked questions
What causes elevated free hemoglobin levels?
What causes low free hemoglobin levels?
How often should this test be repeated?
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