Reference Intervals of Spot Urine Creatinine-to-Osmolality Ratio as a Surrogate of Urinary Creatinine Excretion Rate

Table 8

Special conditions about interpretation of spot urine creatinine-to-osmolality ratio (sUCr/Osm).

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sUCr/Osm tends to underestimate instant urinary excretion rate when:

Lower-than-ordinary Cr excretion load: muscle wasting, obesity, fluid retention (edema or ascites), chronic liver disease, and vegetarians

Decreased tubular Cr excretion: trimethoprim, cimetidine, and famotidine

Increased extrarenal Cr elimination: chronic kidney disease stage 5

Higher daily osmolar load: glycosuria in poorly controlled DM or taking SGLT-2i, extraordinarily large meals, and recent diuretics use

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sUCr/Osm tends to overestimate instant urinary excretion rate when:

Higher-than-ordinary Cr excretion load: cooked meats, and creatine supplements

Increased tubular Cr excretion: nephrotic syndrome

Significant extrarenal osmolar loss: diarrhea, vomiting, gastric juice drainage, and excessive sweating

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Abbreviations: Cr: creatinine; DM: diabetes mellitus; SGLT-2i: sodium-glucose cotransporter-2 inhibitors.