Extremely high myoglobin plasma concentrations producing hook effect in a critically ill patient

Abstract

BackgroundA 21-year old female suffered a cardiac arrest after a one week history of viral illness later shown to be caused by influenza B. The patient required extended cardiopulmonary resuscitation and had further complications including compartment syndrome. MethodsPlasma myoglobin concentration was measured using the Roche Diagnostics electrochemiluminescent myoglobin assay. ResultsThe myoglobin concentration was 205,590μg/l in an undiluted specimen, consistent with severe rhabdomyolysis. Subsequent myoglobin concentrations measured two days later showed dramatic decreases to approximately 1000μg/l, raising suspicion of a hook effect. Dilution and re-analysis of the specimens revealed that the actual myoglobin concentrations were >395,000μg/l, with one specimen possessing an estimated myoglobin concentration of >600,000μg/l. Interestingly, three specimens from this patient did not show evidence of hook effect, with undiluted specimens producing myoglobin concentrations as high as 284,000μg/l. Retrospective analysis of myoglobin results over an 8-year period did not reveal other cases with suspicion of hook effect. The case patient had the highest myoglobin concentrations out of 7301 specimens. ConclusionsThis case illustrates that while the Roche myoglobin assay has a very wide dynamic range, hook effect can occur with extremely high concentrations of plasma myoglobin.