Which units are used for reporting creatinine in blood and in urine?

• A. Blood: mg/dL or mmol/L; Urine: mg/day or mmol/day
• B. Blood: g/dL; Urine: g/day
• C. Blood: mg/dL; Urine: mg/day
• D. Blood: mmol/L; Urine: μmol/day

Answer: (A)

Creatinine is reported in two ways depending on what is being measured: concentration in blood and total amount excreted in urine over time. For blood, it's a concentration in the blood plasma, so mg per deciliter (mg/dL) is the common reporting unit (with SI usage often in μmol/L). For urine, especially when describing 24-hour excretion, it’s the total amount per day, so mg/day or g/day are standard. Using these pairings—concentration in blood (mg/dL) and daily excretion in urine (mg/day)—fits how clinicians interpret renal function and perform calculations like clearance. While SI equivalents exist (μmol/L for blood, mmol/day for urine), mg/day for urine and mg/dL for blood are the traditional, widely used units.