25542 Plasma Hemoglobin (PLHBB)

Determining whether hemolysis is occurring such as from:

-Transfusion reaction

-Mechanical fragmentation of red blood cells

-Relative comparison to baseline levels in extracorporeal membrane oxygenation (ECMO) and centrifugal ventricular assist device (cVAD) patients to assess pump disruption

Results could be falsely elevated due to artifactual red blood cell lysis if not centrifuged within 2 hours of collection.

Test should not be performed on serum; hemoglobin is liberated from red blood cells during clotting and will falsely increase the result.

Drawing blood specimens for plasma hemoglobin measurement should be done with considerable care to avoid causing hemolysis.

Causes of artifactually increased plasma hemoglobin should be excluded and include: forceful aspiration in sample procurement, cannula malposition (high negative-inflow pressures, inadequate pump speed to blood flow ratio), continuous renal replacement therapy, thrombosis or large hematomas.

Bilirubin is a known interference with this assay. Elevated bilirubin levels significantly interfere with the quantitation of the total plasma hemoglobin. In the presence of elevated bilirubin (>5 mg/dL), only oxyhemoglobin will be reported. Trending data should be compared within analytes (ie, total plasma hemoglobin to total plasma hemoglobin; and oxyhemoglobin to oxyhemoglobin) as these represent different components in the blood. Therefore, in the presence of bilirubin, the trend can only be compared with baseline oxyhemoglobin levels.

If bilirubin is above 5 mg/dL, this comment will be added to the report:

Total plasma hemoglobin not reported due to elevated bilirubin interference. Oxyhemoglobin levels are not affected as significantly by bilirubin levels and are more reliable in this setting. If the plasma hemoglobin test is being utilized in a serial fashion, results should be compared within analyte type (eg, oxyhemoglobin to oxyhemoglobin levels for different time points) and using general trends. Because some variability in this test exists, multiple time points should be used to monitor trends and to confirm wide swings in levels. Because pigmented substances may cause nonspecific interference, clinical correlation is required to establish significance of individual test results.

Hemoglobin is contained within erythrocytes and significant amounts of "free hemoglobin" (outside the red blood cell [RBC]) are not normally present in plasma. This free hemoglobin is also called plasma hemoglobin.

Normal blood draw procedures cause a limited degree of unavoidable disruption and therefore a small amount of free hemoglobin may normally be present. When detectable, the total plasma hemoglobin and a subcomponent, oxyhemoglobin, are both reported.

Significant amounts of free hemoglobin occur in plasma following disruption of the RBC for any reason. This might result from a transfusion reaction or mechanical fragmentation of RBCs due to instrumentation, surgical procedures, or mechanical devices. Patients requiring support from extracorporeal membrane oxygenation or centrifugal ventricular assist devices are commonly monitored for trends in plasma free hemoglobin levels to assess for increasing hemolysis. Sharp spikes in plasma hemoglobin levels can indicate pump disruption. However, plasma hemoglobin can be artifactually increased due to a traumatic blood draw or prolonged exposure to post-draw RBCs. Additionally, bilirubin interferes substantially with the ability to calculate total plasma hemoglobin levels and results may be spurious and unreliable. This is a difficulty frequently encountered in serially tested patients. When this occurs, the oxyhemoglobin level tends to show less interference and will be the only analyte reported in the presence of increased bilirubin (>5 mg/dL). When using trending data, total plasma hemoglobin and oxyhemoglobin levels are not interchangeable and should be compared within their subgroups only.

TOTAL PLASMA HEMOGLOBIN

 > or =12 months: 0.0-15.2 mg/dL
Reference values have not been established for patients who are <12 months of age.

OXYHEMOGLOBIN

 > or =12 months: 0.0-12.4 mg/dL
Reference values have not been established for patients who are <12 months of age.

​An elevation in plasma hemoglobin above the reference range indicates likely intravascular hemolysis due to one of the causes listed in the Useful For section.