A 10-year-old male patient was admitted due to intermittent chest pain for 2 months. The chest pain was stabbing in nature

alternating between left and right sides

each episode lasting 1 to 3 seconds

without sweating

palpitations

or fever. He had occasional nasal discharge in the past 3 to 5 days. An outside hospital reported myocardial enzyme panel showing creatine kinase (CK) at 1 168.4 U/L and creatine kinase isoenzyme-MB (CK-MB) at 2 108 U/L

presenting a paradoxical phenomenon of CK-MB>CK

while cardiac troponin Ⅰ(cTnⅠ) within normal limits. Upon admission

repeat myocardial enzyme testing still showed CK-MB>CK

but cardiac troponin and cardiac magnetic resonance imaging were both normal

indicating a discrepancy between laboratory findings and clinical presentation. The laboratory department conducted serial dilution assays to exclude heterophilic antibody interference

followed by polyethylene glycol (PEG) precipitation

which revealed a CK recovery rate of only 24.5%

strongly suggesting the presence of macro-CK. Final confirmation was obtained through CK-MB mass concentration assay showing normal CK-MB levels

leading to the diagnosis of benign macro-CKemia. Benign macro-CKemia can cause falsely elevated CK-MB activity by the immunoinhibition assay

leading to the paradoxical phenomenon of CK-MB > CK

which is not indicative of cardiac injury. It is essential for the laboratory to proactively identify abnormal results and adopt a stepwise verification strategy including dilution test

PEG precipitation

and CK-MB mass assay to avoid misdiagnosis. The patient received no specific treatment and was discharged uneventfully after symptomatic management.