Estimate 24-hour proteinuria from a spot urine sample.
Spot urine PCR (mg/mg) approximates 24-hour protein excretion (g/day). Normal < 0.15. Proteinuria > 3.5 g/day defines nephrotic syndrome. PCR is preferred over 24-hour collection for convenience and reliability. First morning void is most accurate. Used for monitoring CKD progression and preeclampsia screening.