Mr Salloway is admitted to A&E with confusion and malaise. His daughter found him lying on the dining room floor and it is unclear when he fell as she last spoke to him on the telephone 2 days ago. He complains of generalised myalgia but denies any chest pain, shortness of breath or palpitations. He vaguely recalls tripping on the floor lamp lead. Past medical history includes recurrent urinary tract infection, Hypertension and Myocardial infarction 5 years ago. Drug history includes Aspirin, Co-codamol, Atorvastatin and Ramipril. Mr Salloway describes his urine as being dark and urine sample is awaited.
Pulse 72 bpm
Blood pressure 107/80
Respiratory rate 14
Saturations 97% on air
ECG: Q waves in lead 2
A full blood count, renal function test and CRP was requested by the FY1 doctor and results are awaited.
Based on this initial information, what single additional blood test is most likely to be diagnostic?