The excretion of proinsulin and insulin in urine

Proinsulin-like components (PLC) and insulin have been measured in 24 hr urine samples from 8 healthy subjects. The mean excretion of PLC was 45.8 ng and that of insulin 314 ng; the PLC: insulin ratio was 0.14. Urinary PLC was increased 3.5 fold in a patient with a pancreatic islet cell tumor and the PLC: insulin ratio was 0.35. The urinary PLC: insulin ratio is lower than that of serum, presumably because of the relatively lower urinary clearance of the larger molecular weight PLC.