Clinical pharmacy
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The accuracy of creatinine clearance (CLcr) determinations obtained from urine collections of less than 24 hours duration and the cyclical variation in creatinine excretion were studied in 10 critically ill patients with trauma or postoperative complications. Data from patients who received drugs or had diseases known to influence creatinine production or interfere with assay methods were excluded. Twelve consecutive two-hour urine collections and midpoint blood samples were obtained for each patient. ⋯ Mean differences between each 2-hour interval and the 24-hour interval were not significant for the 12 collection intervals. In critically ill trauma or postsurgical patients, the 24-hour CLcr can be estimated from an 8-hour urine collection if a deviation of up to 20% from the 24-hour value is clinically acceptable. No significant cyclical variation in creatinine excretion over 24 hours was found.