Hemoglobin (Hb), Free, Plasma

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Turnaround Time: 2 - 4 days
CPT Code:


Test Type: 1 mL Plasma
Stability Time:



Room temperature

6 days


6 days


6 days

Freeze/thaw cycles

Stable x3

Reference Range:

<5 mg/dL (if conditions are optimal). Values obtained between 5−15 mg/dL should be interpreted with caution since such variables as suboptimal venipuncture may increase results to this range.


Evaluate hemolytic anemia, especially intravascular hemolysis. Plasma hemoglobin is increased with intravascular hemolysis, ABO incompatible transfusion, traumatic hemolysis, falciparum malaria, burns, and march hemoglobinuria. Increase may occur in some cases of extravascular hemolysis, delayed transfusion reaction, slight increase in sickle cell anemia, and β-thalassemia.

High (>20 mg/dL) bilirubin, turbidity, methemalbuminemia, lipemic plasma, and hemolysis during or after venipuncture may cause falsely elevated values in the plasma hemoglobin test (method based on peroxide oxidation of TMB).

Results of this test are labeled for research purposes only by the assay's manufacturer. The performance characteristics of this assay have not been established by the manufacturer. The result should not be used for treatment or for diagnostic purposes without confirmation of the diagnosis by another medically established diagnostic product or procedure.

A pressure bandage should be applied to the site (following the puncture) to stop residual bleeding.

Collection Details:

Patient Preparation:

Patient should not exercise just prior to the test.

Collection Instructions:

Green-top (heparin) tube.

Recommended procedure for collecting sample without inducing hemolysis: An 18-gauge needle with attached infusion tubing is used. Place the tourniquet lightly around the upper arm. Puncture an antecubital vein with as little trauma as possible. Release the tourniquet and clamp the tubing off as soon as blood return is seen. First collect 3 mL blood in a red-top tube with the rubber top off. Then, collect 5 mL in an anticoagulated tube with the top off. Clamp the tubing, withdraw the needle, and apply a pressure bandage to the site until residual bleeding is stopped. Recap the anticoagulant tube and gently mix three to five times. This specimen is used for the plasma hemoglobin determination. Centrifuge and separate plasma from red cells immediately following collection. To avoid delays in turnaround time when requesting multiple tests on frozen samples, please submit separate frozen specimens for each test requested.

Refrigerate at 2°C to 8°C or freeze at -20°C for up to six days.