Value of a screening urinalysis in pregnancy.

In order to assess the value of a screening urinalysis in the detection of urinary tract infection, the results of routine urinalyses from 1,062 obstetric patients were compared to subsequent culture results. A positive urine culture was predicted by pyuria, bacteriuria and a positive nitrite test; the predictive values were 23%, 21% and 87%, respectively. If all the parameters were negative, 96% of the cultures were negative. These findings suggest that in the interest of cost effectiveness, the urine can be cultured only when the screening urinalysis shows pyuria, bacteriuria or a positive nitrite test.