Microscopic hematuria

Chapter 17 MICROSCOPIC HEMATURIA

Definitions of microscopic hematuria vary from 1 to more than 10 red blood cells per high-power field on microscopic evaluation of urinary sediment from two of three properly collected urinalysis specimens. The American Urological Association has issued guidelines (Figs. 17-1 and 17-2) for the evaluation of microscopic hematuria in adults and defines clinically significant microscopic hematuria as three or more red blood cells per high-power field. However, each laboratory establishes its own thresholds on the basis of the method of detection used.

Figure 17-1. Initial evaluation of newly diagnosed microscopic hematuria.

(Adapted from Grossfeld GD, Wolf JS, Litwin MS, et al: Asymptomatic microscopic hematuria in adults: summary of the AUA best practice policy recommendations. Am Fam Physician 2001;63:1145-1154, Figures 1 and 2.)

Figure 17-2. Urologic evaluation of asymptomatic microscopic hematuria.

Dipstick testing for heme lacks specificity, inasmuch as the presence of myoglobin or hemoglobin may result in a positive test result when the urine contains no red blood cells. If the dipstick test is positive, the presence of red blood cells should be confirmed by microscopic examination of the urine. If the urine dipstick test reveals blood, as well as leukocyte esterase, nitrites, and bacteria consistent with urinary tract infection, treatment with antibiotics is appropriate. If the hematuria resolves with treatment, no additional evaluation is necessary, but serum creatinine should be measured.

Microscopic hematuria may be transient, caused by vigorous exercise, mild trauma, sexual intercourse, or by menstrual contamination. If transient microscopic hematuria is suspected, urinalysis should be repeated 48 hours after discontinuation of these activities. Persistent microscopic hematuria warrants further evaluation.

Causes of microscopic hematuria may be classified as either glomerular or nonglomerular in origin. Immunoglobulin A nephropathy is the most common glomerular cause. Nonglomerular causes involving the kidney and upper urinary tract include nephrolithiasis, neoplasm, polycystic kidney disease, medullary sponge kidney, papillary necrosis, hypercalciuria, and hyperuricosuria. Causes involving the lower urinary tract include disorders of the bladder or urethra, such as bladder cancer.

The urinalysis is the most important test in the evaluation of hematuria because it often distinguishes glomerular from nonglomerular bleeding. If proteinuria is detected on dipstick testing, total urinary protein excretion should be quantified. Twenty-four-hour urinary protein excretion of more than 300 mg suggests the kidney as a source of microscopic hematuria. Other findings that support a glomerular cause include renal insufficiency, red blood cell casts, or dysmorphic red blood cells. When glomerular bleeding is suggested, no urologic evaluation is necessary. Proteinuria or renal insufficiency with microscopic hematuria warrants referral to a nephrologist for evaluation and possible renal biopsy.

If a glomerular source is ruled out or considered unlikely, the upper urinary tract should undergo imaging. Excretory urography, ultrasonography, computed tomographic (CT) scanning, or magnetic resonance imaging (MRI) may be used. A CT scan without contrast medium is appropriate as the first test for patients with suspected urinary stone disease. When there is no clinical suspicion of urinary stone disease, CT urography should be performed, first without and then with contrast medium. CT scanning is more expensive than excretory urography and ultrasonography, but it is the best imaging modality for the evaluation of urinary stones, renal and perirenal infections, and associated complications. In addition, with excretory urography and ultrasonography, additional imaging is often necessary for further evaluating cysts. When CT scanning is unavailable, excretory urography or ultrasonography are reasonable alternatives individually or in combination. Ultrasonography is advised in place of CT scanning for patients with renal failure, pregnancy, or hypersensitivity to contrast medium.

The source of microscopic hematuria is not found in about 70% of cases after urinalysis for evidence of glomerular hematuria and imaging of the upper urinary tract. The work-up usually proceeds with evaluation of the lower urinary tract. Cystoscopy is appropriate if risk factors for bladder cancer are present. Cytologic analysis of voided urine is less sensitive than cystoscopy in the detection of bladder cancer, but it has high specificity. The sensitivity is improved if specimens of urine are obtained from the first voiding in the morning on 3 consecutive days.

Patients at risk for significant disease include those with a history of smoking or analgesic abuse; those with occupational exposure to benzenes or aromatic amines; those older than 40 years; those with a history of gross hematuria, urologic disease, irritative voiding symptoms, or urinary tract infection; and those with a history of pelvic irradiation.

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