Urine Analysis

Urine analysis involves the following:

Urine dipstick

Urine dipstick accuracy in predicting UTI has been widely reported [7]. Nitrite sensitivity alone is 81%, that of leucocytes (leucocyte esterase) alone is 77%. If both are present, sensitivity is 94%. Nitrites are only converted from nitrates in the presence of certain bacteria including E.coli.

Other common pathogens including staphylococcus saprophyticus are not nitrite producing. Nitrites are more specific for the diagnosis of UTI. For example, interstitial nephritis can cause pyuria. However, if the diagnosis of UTI is made purely on the dipstick result of positive nitrites and leucocytes (with positive culture taken as gold standard), the overtreatment rate has been estimated as 47% and the undertreatment rate has been estimated as 13%, illustrating its inability to predict UTI accurately [7].

Urine microscopy

Urine microscopy is also available to the ED physician. Classically, the presence of more than 10 WBCs per mm2 is consistent with a diagnosis of UTI. Most labs now use automated assays of cell counts. When compared to dipstick, the earlier reported over and undertreatment rates were similar and because of the time-consuming nature of microscopy, dipstick remains the screening test of choice in most cases [7].

Learning bite

It is important to understand that a negative urinanalysis does not exclude a UTI. This is especially the case if the pretest probability is high, for example, if there is a history of one or more symptoms or previous UTI.

Urine culture

Urine culture remains the gold standard for detection of UTI, but as discussed earlier, it is not required in all patients. However, the consensus remains that all patients with suspected pyelonephritis, and all complicated UTIs should have their urine sent for culture before initiating antibiotics. The presence of >105 per ml confirms significant bacteriuria.