HEMATURIA (microscopic)

31 HEMATURIA (microscopic)

General Discussion

Definitions of microscopic hematuria vary from one to more than 10 red cells per high-power field. The American Urological Association has issued guidelines 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 on microscopic evaluation of urinary sediment from two of three properly collected urinalysis specimens. However, each laboratory establishes its own thresholds based on the method of detection used.

Dipstick testing for heme lacks specificity, since the presence of myoglobin or hemoglobin may result in a positive test when the urine contains no red cells. If the dipstick test is positive, the presence of red cells should be confirmed by microscopic examination of the urine. If the urine dipstick 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. IgA nephropathy is the most common glomerular cause. Nonglomerular causes involve the kidney and upper urinary tract and 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, urethra, and prostate such as bladder and prostate 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 greater than 300 mg suggests the kidney as a source of microscopic hematuria. Other findings that support a glomerular etiology include renal insufficiency, red 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 be imaged. Excretory urography, ultrasonography, CT, or MRI may be used. A CT scan without the use of contrast is appropriate as the first test for patients with suspected stone disease. When there is no clinical suspicion of stone disease, CT urography should be performed first without contrast and then with contrast. CT is more expensive than excretory urography and ultrasonography, but is the best imaging modality for the evaluation of urinary stones, renal and perirenal infections, and associated complications. In addition, excretory urography and ultrasonography often require additional imaging to further evaluate cysts. When CT is unavailable, excretory urography or ultrasound are reasonable alternatives individually or in combination. Ultrasonography is advised in place of CT 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 and in older men with asymptomatic microscopic hematuria. Cytologic analysis of voided urine is less sensitive than cystoscopy in the detection of bladder cancer, but 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 smoking history; occupational exposure to benzenes or aromatic amines; age over 40 years; history of gross hematuria; history of urologic disease; history of irritative voiding symptoms; history of urinary tract infection; history of pelvic irradiation; or analgesic abuse.

A thorough evaluation of the urinary system may fail to identify a source of microscopic hematuria in 19–68% of patients. In patients with a negative initial evaluation of asymptomatic microscopic hematuria, consideration should be given to repeating urinalysis, voided urine cytology, and blood pressure determination at 6, 12, 24, and 36 months. Additional evaluation, including repeat imaging and cystoscopy, may be warranted in patients with persistent hematuria in whom there is a high index of suspicion for significant underlying disease. If gross hematuria, abnormal urinary cytology, or irritative voiding symptoms in the absence of infection develop, reevaluation should be undertaken immediately. This may include cystoscopy, urinary cytology, or repeat imaging.

Tags: Instant Work-ups A Clinical Guide to Medicine

Aug 17, 2016 | Posted by admin in PEDIATRICS | Comments Off

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