Air-exposed urine dipsticks give false-positive results for glucose and false-negative results for blood.

Urine dipstick jars often are left uncapped, which led the authors to wonder what effect prolonged air exposure might have on dipstick accuracy. Unexpired Ames Multistixs (Miles Inc., Elkhart, IN) were exposed to ambient air for intervals of up to eight weeks and were used to test urine for the presence or absence of blood, protein, and glucose. Multistixs were read by a blinded participant. A urine sample reading negative for glucose with unexposed (control) Multistixs tested trace positive with three of three Multistixs exposed for 7 days, and 1+ (three of six) or trace positive (three of six) (P less than 0.05) with Multistixs exposed for 28 days. A urine sample reading 1+ for blood with controls tested negative with five of six (P less than 0.05) and six of six (P less than 0.05) Multistixs exposed for 28 and 56 days, respectively. Protein detection was accurate up to 56 days. The authors conclude that urine dipstick jars should be recapped to avoid prompting needless evaluations of glucosuria or delaying detection of important causes of microscopic hematuria.