A 54-year-old female patient was admitted to the hospital for dysphagia lasting 10 days and retrosternal pain for 10 hours. She had a past medical history of cerebral infarction and myocardial ischemia

and had been taking atorvastatin and other medications on a long-term basis. No significant positive signs were found on physical examination at admission. Routine biochemical tests detected a creatine kinase (CK) activity of 646 U/L and a CK-MB activity of 1 241 U/L

showing an abnormal pattern where CK-MB activity was markedly higher than total CK activity. Through stepwise diagnostic workup including sample dilution test

CK-MB mass assay

cranial magnetic resonance imaging (MRI) and polyethylene glycol (PEG) precipitation test

the abnormality was finally attributed to macro creatine kinase (macro CK) interference. Proactive identification of abnormal results by the clinical laboratory

followed by verification with methods such as dilution test

CK-MB mass assay and PEG precipitation

is critical to avoiding misdiagnosis and mistreatment.