Microscopic Hematuria in Adults
A Finding of Blood in the Urine During Routine Exams is Common
Jul 16, 2009
Hematuria is the presence of red blood cells in the urine. Microscopic hematuria—that which is not visible to the naked eye—is a frequent finding during routine physical examinations, urine drug screens, or evaluations for health insurance coverage.
Due to variability in evaluation of specimens—most are initially subjected only to “dipstick” testing, which cannot distinguish between red blood cells and certain other substances in the urine—patients are understandably confused when they are simply told they have blood in their urine.
Any urine specimen that demonstrates “hematuria” by dipstick evaluation should be further evaluated microscopically to confirm the presence of red blood cells (RBCs). The absence of RBCs suggests the presence of either myoglobin or hemoglobin, which can be mistaken for RBCs on dipstick tests.
Because there has been a lack of consensus among the medical community as to what constitutes clinically significant hematuria, estimates of the prevalence of asymptomatic hematuria among the adult population range from 0.19 to 21 percent. (Grossfeld G, et al. Asymptomatic microscopic hematuria in adults: summary of the AUA best practice policy recommendations. Am Fam Physician 2001;63:1145-54)
The American Urological Association (AUA) has defined clinically significant microscopic hematuria as three or more RBCs per high-power field on microscopic evaluation of urinary sediment from two of three properly collected urinalysis specimens.
Causes of microscopic hematuria range from benign and incidental to life-threatening, so confirmation of clinically significant hematuria on two specimens should never be taken casually.
Causes of Microscopic Hematuria
Since there are so many potential explanations for blood in the urine, the recognized causes are divided into categories that enable physicians to standardize their approach to diagnosis and management (the list below is partial):
Glomerular Causes (originating within the filtration unit of the kidney)
- Immune-mediated conditions, such as systemic lupus erythematosus, Goodpasture’s syndrome, IgA nephropathy, membranoproliferative glomerulonephritis, or Wegener’s granulomatosus
- Genetic conditions, such as Fabry’s disease, benign familial hematuria, or Alport’s syndrome
- Inflammatory or post-infectious conditions, such as Henoch-Schönlein purpura, post-streptococcal glomerulonephritis, endocarditis, or post-viral glomerulonephritis
Non-Glomerular Causes (within the kidney, but not confined to the filtration units)
- Genetic conditions, such as polycystic or multicystic kidney disease, medullary cystic disease, or hereditary nephritis
- Metabolic conditions, including hypercalciuria or hyperuricosuria
- Infections, such as tuberculosis or pyelonephritis (e.g., from untreated bladder infections)
- Interstitial nephritis (inflammation of the structural cells of the kidney) caused by viral or bacterial infections, medications, or autoimmune disease
- Renal cysts
- Renal cell carcinoma
- Vascular anomalies, such as those due to uncontrolled hypertension, thromosis of a renal artery or vein, or sickle-cell disease
Extrarenal Causes (outside the body of the kidney)
- Benign prostatic hypertrophy
- Overzealous anticoagulation (e.g., warfarin, heparin, etc.)
- Kidney stones
- Congenital or acquired structural abnormalities (strictures, posterior ureteral valves, etc.)
- Infections (bladder, prostate, epididymis, urethra)
- Cancer (bladder, urethra)
Other Causes
- Contamination from menstruation
- Exercise hematuria
- Sexual intercourse
(From McDonald M, et al. Assessment of microscopic hematuria in adults. Am Fam Phys 2006;73(10):1748-54)
Management of Microscopic Hematuria
- If a benign cause of hematuria is suspected (intercourse, vigorous exercise, menstruation, etc.), repeat urinalysis 48 hours after cessation of the inciting cause should show resolution of the hematuria. Cancers, however, can also cause intermittent or transient hematuria.
- If a urinary tract infection is identified, antibiotic treatment should lead to resolution.
- If an infection or harmless transient hematuria is not identified, a search for glomerular causes is typically initiated. This would entail more detailed urinalysis, 24-hour urine collections to evaluate for protein loss and glomerular function, blood tests, and possibly a kidney biopsy.
- Once glomerular causes are excluded, non-glomerular causes are sought. This usually requires radiologic imaging of the upper urinary tract (intravenous urography, ultrasound, CT, etc.). Urine cytology (examination of cells in urine for cancerous changes) and cystoscopy (visual examination of the lower urinary tract via a tubular scope) are usually recommended for individuals over the age of 40.
- Depending on the age of a patient and other historical details and physical findings, many of these tests may be conducted in concert to save time, money, and emotional stress.
Although microscopic hematuria is a common finding during routine medical evaluations, and most cases have benign underlying causes, it is prudent to follow the instructions of one’s physician until the reason for the hematuria has been diagnosed.
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