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.