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Hemoglobin (Hb) Free Blood Test

A Hemoglobin Free Test to evaluate hemolytic anemia, especially intravascular hemolysis. 

Sample Report

Test Code: 005595

Also Known As: Free Hemoglobin; Hb Solubility; Hemoglobin; Free; Plasma Free Hemoglobin

Methodology: Based on the catalytic action of hemoglobin on the oxidation of TMB by hydrogen peroxide; rate measured by spectrophotometry

Preparation: No fasting required. Avoid exercise prior to testing.

Test Results: 4-5 days once the lab receives the specimen. May take longer based on weather, holiday or lab delays.


Hemoglobin (Hb) is the main component of red blood cells. It is a protein that carries oxygen. This test is useful in diagnosing or monitoring how severe hemolytic anemia is. This is a disorder in which a low red blood cell count is caused by the abnormal breakdown of red blood cells.

This test is useful in determining:

  • Transfusion reaction
  • Paroxysmal nocturnal hemoglobinuria (PNH)
  • Mechanical fragmentation of red blood cells
  • Thalassemias
  • Cardiopulmonary bypass or mechanical heart valve-induced anemia
  • Sickle-cell disease (SCD)
  • Hereditary spherocytosis
  • Pyruvate kinase deficiency
  • Relative comparison to baseline levels in extracorporeal membrane oxygenation (ECMO) and centrifugal ventricular assist device (cVAD) patients to assess pump disruption



Hemoglobin is contained within erythrocytes and significant amounts of "free hemoglobin" (outside the RBC) is not present in plasma in normal states. This free hemoglobin is also called plasma hemoglobin.

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