Content area
Full Text
TO THE EDITOR: I would like to comment on the article on acute pyelonephritis by Drs. Ramakrishnan and Scheid1 in the March 1, 2005, issue of American Family Physician. Table 3 of this article1 details the laboratory diagnosis of urinary tract infections (UTIs). According to data in this table, the urinary nitrite test has a sensitivity of 92 to 100 percent and a specificity of 35 to 85 percent for diagnosing UTI. The reference cited for these estimates is a 1983 review article,2 not a primary data source.
Multiple references support different sensitivity and specificity numbers. For example, Campbell's Urology states that "the specificity of the nitrite dipstick for detecting bacteriuria is over 90 [percent]. The sensitivity of the test, however, is considerably less, varying from 35 [percent] to 85 [percent]."3
A meta-analysis4 that included sensitivity and specificity of nitrite and leukocyte esterase for UTI found that the sensitivity of nitrite clustered around 50 percent, and the specificity averaged around 95 percent. For leukocyte esterase, sensitivity appeared highly variable depending on study and setting but reasonably can be inferred to be in the 50 to 60 percent range. Its specificity also was highly variable but, on average, was lower than that of nitrite.4
A study5 of symptomatic men with UTI in primary care found urinary nitrite to have a sensitivity of 38 percent and a specificity of 84 percent; leukocyte esterase had a sensitivity of 54 percent and a specificity of 55 percent.
The reference cited in the table1 to support their data states: "These sticks [nitrite test sticks] are 90.7...