Creatinine is a waste product formed from muscle metabolism and excreted by the kidneys.

Measuring creatinine in a spot urine sample helps assess urine concentration and provides a baseline for calculating ratios with other analytes.

Clinical uses include:

Evaluating renal function and tubular handling of substances.

Standardizing spot urine tests (protein/creatinine ratio, calcium/creatinine ratio, microalbumin/creatinine ratio).

Detecting abnormal urine concentration due to dehydration, renal disease, or muscle disorders.

Often performed alongside serum creatinine and estimated GFR for a complete renal profile.

Analyte: Creatinine in urine (mg/dL or mmol/L).

Normal Range (varies by lab and age): Typically ~20–320 mg/dL in random urine samples.

Abnormal Findings:

Low urine creatinine: Dilute urine, renal dysfunction, muscle wasting.

High urine creatinine: Concentrated urine, high muscle mass, dehydration.

Clinical Use:

Provides a marker of urine concentration and kidney excretion capacity.

Helps guide interpretation of other spot urine tests.

Supports nephrology and metabolic evaluations.