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Urology (Expert Forum)
Microhematuria: accuracy of dip stick vs. microscopic analysis
Questions in the Urology forum are answered by Dr. Stephen Liroff, affiliated with the Henry Ford Hospital. Topics covered include benign prostate disease, penis curvature, cystisis, kidney stones, pediatric urology, prostate, sexual dysfunction, urinary tract infections (UTI), and urological cancers.
Microhematuria: accuracy of dip stick vs. microscopic analysis
by DR, Sep 09, 1999 12:00AM
During a routine physical, my urinalysis, performed in the Dr.'s office,(using dipstick?) showed microhematuria. My doctor requested I come back after several weeks for another test, (also performed in the office)which was also positive. After the third positive test, she ordered an IVP and renal ultrasound, both of which were negative. She had me come back in again a month later and give another urine sample. This time, the sample tested positive in the office, but the same sample was also sent to the lab for microscopic analysis. The lab results indicated "no blood seen". Now I am wondering if the dip stick tests (or whatever method they used in the doctors office) could have been inaccurate all along. Is the microscopic analysis considered the definitive test, and is it possible for a dip stick test to be consistently inaccurate? If so, what could account for the false-positive results? If dip stick tests are sometimes inaccurate (as the nurse told me), then why aren't all positive dip stick tests sent in for microscopic analysis before the patient undergoes more invasive testing? Your response is greatly appreciated. DR
Doctor's Answer
by HFHS M.D.-BE, Sep 13, 1999 12:00AM
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Dear DR,
The use of urinary dipstick is a quick and inexpensive method to detect abnormal substances in urine. These include blood, protein, white blood cells, glucose and ketones among other things. As far as detection of blood goes, the dipstick is almost 90% sensitive (i.e., the probability of detecting blood when it actually is present). However, its specificity (i.e., the probability that the test would identify the absence of blood, when such is the case) is somewhat lower, indicated by its high false-positive rate. That is why the efficacy of urinary dipstick in screening hematuria (blood in urine) to identify patients with significant urologic disease is controversial.
False-positive readings in a dipstick test could be due to a concentrated urine ( as in the urine of a dehydrated patient) and exercise, as well as use of large amounts of vitamin C as well other foods and vitamins with high concentration of oxidants. In pre-menopausal women, contamination of the urine with menstrual blood could be the source of blood, leading to a full work-up unnecessarily.
Of course, the gold standard is the microscopic analysis, which is done in the lab. It is indeed wise to verify a positive dipstick with microscopy, especially in the absence of risk factors and signs/symptoms. A urine culture and urine cytology test ( to detect if any abnormal cells are present in the urine) is also in order. The usual work-up of hematuria should take the above into account.
This information is provided for general medical educational purposes only. Please consult your physician for diagnostic and treatment options pertaining to your specific medical condition. More individualized care is available at the Henry Ford Hospital and its satellites (1 800 653-6568).
Sincerely,
HFHS M.D.-BE
*keyword: urine dipstick and hematuria
Dear DR,
The use of urinary dipstick is a quick and inexpensive method to detect abnormal substances in urine. These include blood, protein, white blood cells, glucose and ketones among other things. As far as detection of blood goes, the dipstick is almost 90% sensitive (i.e., the probability of detecting blood when it actually is present). However, its specificity (i.e., the probability that the test would identify the absence of blood, when such is the case) is somewhat lower, indicated by its high false-positive rate. That is why the efficacy of urinary dipstick in screening hematuria (blood in urine) to identify patients with significant urologic disease is controversial.
False-positive readings in a dipstick test could be due to a concentrated urine ( as in the urine of a dehydrated patient) and exercise, as well as use of large amounts of vitamin C as well other foods and vitamins with high concentration of oxidants. In pre-menopausal women, contamination of the urine with menstrual blood could be the source of blood, leading to a full work-up unnecessarily.
Of course, the gold standard is the microscopic analysis, which is done in the lab. It is indeed wise to verify a positive dipstick with microscopy, especially in the absence of risk factors and signs/symptoms. A urine culture and urine cytology test ( to detect if any abnormal cells are present in the urine) is also in order. The usual work-up of hematuria should take the above into account.
This information is provided for general medical educational purposes only. Please consult your physician for diagnostic and treatment options pertaining to your specific medical condition. More individualized care is available at the Henry Ford Hospital and its satellites (1 800 653-6568).
Sincerely,
HFHS M.D.-BE
*keyword: urine dipstick and hematuria
