Microscopic Hematuria: What It Means
Frederick R. Jelovsek MD
"What does blood in the urine from the urinalysis indicate? You can't really see in urine, but it is detected through the urine test. Background is a 42 year old, diabetic, who gets very sick when ill because of diabetes" J.E.
Blood in the urine that cannot be seen with the naked eye and is only detected through urine dip strip chemical tests or microscopic analysis is called microscopic hematuria. The most common cause of microscopic hematuria is simply unknown and not a cause for concern if major problems have been ruled out. It is estimated that possibly up to 20% of adult men and postmenopausal women have microscopic hematuria. The cause for the microscopic bleeding may only be found in as few as 30-40% of patients undergoing a full urologic work up.
Microscopic hematuria is defined as more than 3 red blood cells per high power microscopic field in a centrifuged urine specimen. Routine urinalysis to check for hematuria in an asymptomatic patient during an annual routine exam is not recommended. This is because of the very high incidence of false positives for serious problems and because the work up includes several expensive and slightly risky procedures. In the case of someone with diabetes, however, the testing should be routine because of concern that diabetes can affect the kidneys and cause a diabetic nephropathy that spills blood cells in the urine. Once microscopic hematuria is discovered, women should undergo studies to make sure there are no serious causes of the blood in the urine. Bladder inflammation is a common cause in women but other serious causes should be sought out.
One study found that microscopic hematuria was significantly higher in women, in those under 49 years of age, in hypertensive subjects, in smokers or ex-smokers, in those who used non-steroidal anti-inflammatory drugs during the prior 6 months and in chemical industry workers.
Can the urine test be wrong about having blood in the urine?
Yes. There are instances of false positive and false negative urine dip strip chemical tests. If a microscopic analysis is performed by a reliable laboratory technician or health provider, then that will confirm that the urine dip strip test is a true positive. The chemical tests on urine strips pick up about 90-100% of all microscopic hematuria. False positives include a specimen contaminated with vaginal or menstrual bleeding, Betadine® solution, myoglobinuria (breakdown of muscle cells in the urine), moderate to severe dehydration, and bacterial enzymes from vaginal or bladder infections. Vitamin C (ascorbic acid) can produce false negative tests as can a very acid urine (pH 5.0 or less) or test strips that have been over exposed to the air or outdated.
What are the serious diseases that microscopic hematuria can represent?
Damage to the kidney filtration system (glomeruli) or the rest of the kidney tissue (interstitial or papillary) by diseases or even medications is a serious condition. If the damage is severe enough, kidney failure will be the final result. The list of medical diseases and medications that can damage kidney function is extensive. Chronic pain medicine use such as arthritis medicine is a common cause of renal damage. Anticoagulants such as coumadin and even aspirin can cause blood in the urine but it is a mistake to assume the cause of microscopic hematuria is the anticoagulant until serious causes have been ruled out.
In the case of someone with diabetes, there is concern for the disease itself causing papillary necrosis of the kidney or a glomerular nephritis. Diabetic medications such as Glucophage® (metformin) can also damage the kidneys. Women with diabetes are often taking antihypertensive medications and diuretics (water pills) which can sometimes damage the kidneys. Therefore, it is doubly important to investigate any kidney tissue damage when someone with diabetes has microscopic hematuria.
Anatomical causes of bleeding such as kidney stones, kidney cancer, bladder cancer and kidney or bladder infections are also serious conditions meriting early diagnosis.
What studies need to be done to make sure none of the serious conditions are present?
The work-up of microscopic hematuria should be directed toward any known medical problems that could cause blood in the urine. If a woman is entirely asymptomatic, then the work-up usually includes lab studies, an IVP and a cystoscopy. In most cases, these should be able to indicate a cause or where additional investigative studies or procedures are needed.
Work-up of Asymptomatic Hematuria
|non kidney||lab studies -
coagulation studies, prothrombin time (PT), partial thromboplastin time (PTT), complete blood count (CBC)
|kidney||lab studies -
BUN, creatinine, creatinine clearance, microscopic urinalysis, urine culture
radiologic studies -
intravenous pyleogram (IVP)
|bladder||lab studies -
urinalysis, urine culture, urine cytology
Does the amount of blood in the urine indicate the seriousness of the condition?
In general, no, if we are talking about microscopic blood. With microscopic hematuria, whether there are 5 red blood cells in the urine or 50 does not seem to correlate with how severe a condition is or how long it has been present. Also, microscopic blood is more often associated with upper tract kidney disease rather than lower tract bladder tumors or infections.
Grossly visible blood in the urine is more commonly associated with lower tract disease. In one study, cancer and other benign tumors were found only about 1% of the time in patients with microscopic hematuria while 22% of patients with gross blood in the urine had either benign or malignant urological tumors.
In summary, once microscopic hematuria is found, a work up for diseases affecting kidney function should be started. While the likelihood of cancer is low (1-2%) other long term problems can be found.
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