A study on the reliability of dipstick urinalysis

The objective of this study is to determine the reliability of the Ames automated method as a screening procedure for the detection of red blood cells and leukocytes. 5486 urines were analyzed by an automated dipstick technique. 3127 urines were completely negative on the stick and 2359 showed a positive finding. All 2359 dipstick positive urines and 456 of the 3127 dipstick negative urines (total of 2815) were read blindly by one of two nephrologists working on different days, 1743 by M. K. and 1072 by P. S. Red cells, leukocytes and casts were enumerated per high power field and compared to the dipstick findings. Urines that were negative by dipstick for protein, blood leukocytes, nitrites, glucose and ketones were generally negative on microscopic examination, with only 5.3% having any abnormality. Urines positive for one or more of these findings correlated poorly with the microscopic findings due to the number of false positive and false negative dipsticks for red cells and leukocytes. Sensitivities were 75.3% and 81.0% and specificities were 88.6% and 64.3%, for red cell and leukocytes, respectively. Increasing the dipstick cutoff point improved sensitivity but lowered specificity. Urines positive for glucose and ketones had lower sensitivities for the detection of leukocytes, but not urines positive for protein. Microscopic examination should be done on dipstick abnormal urines. This may not be necessary for negative urines unless specifically indicated for clinical reasons. Urines positive for ketones or glucose should be screened systematically since they give a larger proportion of false negatives for leukocytes.