Free Hemoglobin in Plasma (Quantitative)
This test measures the amount of free hemoglobin—unbound to red blood cells—in your plasma, which can help assess conditions affecting red blood cell breakdown or release.
["Free hemoglobin in plasma may signal red blood cell destruction or abnormal release into circulation."]
Key facts at a glance
- LOINC
- 720-3
- Short code
- Hgb Free Plas Ql
- Synonyms
- Hgb Free Plas Ql
- 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
Why This Test Might Be Ordered
Your healthcare provider may recommend this test if you have symptoms like fatigue, pale skin, or signs of hemolysis (red blood cell destruction), or if you’re being evaluated for conditions like sickle cell disease, autoimmune hemolytic anemia, or certain medications that affect red blood cells.
What to Expect Before the Test
No special preparation is needed. You’ll provide a blood sample drawn from a vein, similar to other routine blood tests. The sample is processed to separate plasma from red blood cells before analysis.
How the Test Works
The test uses a specialized method to detect free hemoglobin in your plasma, which is distinct from hemoglobin bound to red blood cells. This helps differentiate between sources of hemoglobin in your bloodstream.
What the Results Mean
Elevated levels may indicate conditions like hemolysis, where red blood cells break apart prematurely, or certain medications or diseases that release hemoglobin into plasma. Lower levels may be normal or could relate to other factors like hydration status or red blood cell production.
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.
Free hemoglobin in plasma is primarily useful in diagnosing or monitoring conditions that involve abnormal red blood cell destruction or release, such as hemolytic anemia, intravascular hemolysis, or certain toxic exposures. It can also help guide treatment decisions in patients with known red blood cell disorders.
Short name
Free Hemoglobin (Plasma)
Frequently asked questions
What causes free hemoglobin to be elevated?
How is this test different from a regular hemoglobin test?
Can lifestyle changes affect free hemoglobin levels?
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