Figure 72

Culture interpretation. Urinalysis must examine bacterial and leukocyte counts (per milliliter). An approximate way of estimating bacterial counts in the urine uses a dip-slide method: a plastic paddle covered on both sides with culture medium is immersed in the urine, shaken, and incubated overnight.

The most specific results, however, are provided by laboratory analysis, which allows precise counting of bacteria and leukocytes. Normal values for a midstream specimen are less than or equal to 105 Escherichia coli organisms and 104 leukocytes per milliliter. These classical "Kass criteria," however, are not always reliable. In some cases of incipient cystitis the number of E. coli per milliliter can be lower, on the order of 102 to 104 [4]. When fecal contamination has been ruled out, growth of bacteria that are not normally urethral saprophytes indicates infection. This is the case for Pseudomonas, Klebsiella, Enterobacter, Serratia, and Moraxella, among others, especially in a hospital setting or after urologic procedures.

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