Which test requires a 24-hour urine specimen?

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Multiple Choice

Which test requires a 24-hour urine specimen?

Creatinine clearance requires a 24-hour urine collection to estimate kidney filtration accurately. Creatinine is produced by the body's muscles at a relatively steady rate, so capturing all urine over a full day provides the total amount of creatinine excreted in that period. When this daily urine creatinine is paired with the plasma creatinine level, you can calculate how effectively the kidneys are clearing creatinine—and by extension, estimate the glomerular filtration rate. To do this correctly, you typically start by discarding the first morning urine, then collect every subsequent void for 24 hours, keeping the specimen refrigerated, and finally measure the total urine volume and send the sample for creatinine analysis (with a blood sample for plasma creatinine as well). The other tests don’t use this 24-hour urine approach. Urine culture and sensitivity rely on a single urine specimen to grow bacteria and test antibiotic susceptibility. Fibrin split products are measured from a blood sample to assess coagulation activity, not urine. The glucose tolerance test uses timed blood samples after drinking a glucose solution, not a 24-hour urine collection.

Creatinine clearance requires a 24-hour urine collection to estimate kidney filtration accurately. Creatinine is produced by the body's muscles at a relatively steady rate, so capturing all urine over a full day provides the total amount of creatinine excreted in that period. When this daily urine creatinine is paired with the plasma creatinine level, you can calculate how effectively the kidneys are clearing creatinine—and by extension, estimate the glomerular filtration rate. To do this correctly, you typically start by discarding the first morning urine, then collect every subsequent void for 24 hours, keeping the specimen refrigerated, and finally measure the total urine volume and send the sample for creatinine analysis (with a blood sample for plasma creatinine as well).

The other tests don’t use this 24-hour urine approach. Urine culture and sensitivity rely on a single urine specimen to grow bacteria and test antibiotic susceptibility. Fibrin split products are measured from a blood sample to assess coagulation activity, not urine. The glucose tolerance test uses timed blood samples after drinking a glucose solution, not a 24-hour urine collection.

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