Patients with flank pain and suspected renal lithiasis are often evaluated for hematuria by dipstick or microscopic urinalysis. Because the presence of hematuria has been labeled an indicator of renal lithiasis, some authors suggest that no further work-up is necessary. However, there is no consensus as to what constitutes hematuria by microscopy or how to proceed with patients who have hematuria and flank pain. Bove and colleagues reassessed the value of hematuria as a predictor of renal lithiasis using a newer computed tomographic (CT) scanner.
A total of 267 patients with acute flank pain was referred for unenhanced helical CT scan of the renal system. Before the CT scan, the patients had a urinalysis performed by dipstick or microscopy. The researchers classified hematuria as greater than zero, greater than 1 or greater than 5 red blood cells per high power field. The dipstick urinalysis was positive for hematuria if the appropriate color change occurred. Using the helical CT scan as the standard, the authors calculated the sensitivity, specificity, positive and negative predictive values and accuracy of microscopic- or dipstick-positive hematuria with regard to renal lithiasis. Both tests were accurate 50 percent of the time.
Of the 183 patients who had a positive dipstick test for hematuria, 92 did not have renal lithiasis, and 91 did. Of the 195 with microscopic hematuria, 100 did not have renal lithiasis, and 95 did. The sensitivities for dipstick, microscopy and the two tests combined ranged from 67 to 89 percent, but the positive predictive value range was 54 to 65 percent. The accuracy of the tests ranged from 57 to 67 percent.
The authors conclude that the presence of hematuria in acute flank pain is a poor predictor of ureterolithiasis. They added that the presence or absence of hematuria in patients with flank pain can be misleading. In patients with acute renal colic, a positive or negative hematuria test should not determine whether a more definitive evaluation should be performed.
editor's note: This is a classic example of using the results of a time-honored procedure (such as performing a urinalysis in patients with flank pain) to determine the next diagnostic or treatment option. In this study, the results of the urinalysis provided the right information only one half of the time. Physicians need to rely more on clinical evaluation and a more definitive diagnostic examination.—k.e.m.