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

Area of Science:

• Clinical Chemistry
• Diagnostic Assays
• Biomarker Analysis

Background:

• A 21-year-old female experienced cardiac arrest following a viral illness, later identified as influenza B.
• The patient required extensive cardiopulmonary resuscitation and developed compartment syndrome.

Observation:

• Initial plasma myoglobin measurements were falsely low (205,590 μg/l) due to the hook effect, masking severe rhabdomyolysis.
• Re-analysis with dilution revealed actual myoglobin concentrations exceeding 395,000 μg/l, with one specimen over 600,000 μg/l.

Findings:

• The Roche Diagnostics electrochemiluminescent myoglobin assay exhibited a hook effect at extremely high myoglobin concentrations.
• This phenomenon was not observed in other specimens or retrospectively in 7301 samples over 8 years, indicating a rare occurrence.

Implications:

• Clinicians must be aware of the potential for hook effect in assays when dealing with suspected severe rhabdomyolysis.
• Assay limitations, even with wide dynamic ranges, necessitate careful interpretation of results in critical cases.