Summary

A 76-year-old woman (51 kg, 158 cm, body mass index 20.5) was admitted to the hospital because of an acute kidney injury with hyperkalemia. On admission, she reported progredient muscle weakness of all limbs for several days. Serum potassium level was dramatically elevated and ECG showed QRS with a ‘sine-wave’ pattern and haemodialysis was started. 45 days ago, Hartmann’s operation was done because of stenosing sigmoid diverticulitis. At this time, the serum creatinine was 0.4 mg/dl (‘normal’ 0.5–1.2). Thereafter, she got severe ‘high output-ileostoma’ with severe intestinal fluid losses and treatment with potassium supplementation and spironolactone was started by the surgeons. She was discharged with elevated serum potassium levels and serum creatinine of 1.0 mg/dl (‘normal’ range (0.5–1.2 mg/dl)). This case illustrates impressively the lack of serum creatinine as an ideal kidney function test, because it is depending on muscle mass and there is no interindividual normal range.