Follow-up testing for ketonuria: Is it necessary?

The authors examined the utility of confirming positive urinary ketones detected by Multistix(TM) and the designation of trace ketonuria by Acetest(TM). They also studied whether ketonuria should signal a need for microscopic evaluation. They used Multistix to test for ketones in 4345 urine samples; 108 samples tested positive and were retested using Acetest. The positive predictive value for Multistix was 98% for samples of small amounts or more of ketonuria. Sensitivity and specificity were then assessed on 179 samples tested prospectively by both methods. Multistix specificity was high at 96%, but sensitivity decreased from 87.5% to 63.6% when trace ketonuria was regarded as positive ketonuria. In evaluating the usefulness of positive ketonuria to signal a need for microscopic examination, the authors found 12% of 78 ketotic, but otherwise negative, samples demonstrated positive microscopic findings compared with 15% for 114 chemically negative controls. The authors concluded that using Acetest for confirmation is necessary only for trace ketonuria by Multistix and that confirmatory testing of higher levels of ketonuria incurs increased costs without adding significantly to patient care. Using more sensitive Acetest detection levels does not change these results. In addition, ketonuria does not appear to signal a need for further microscopic evaluation.