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Investigating hematuria
The search for clues to underlying
disease
BY Trevor J. Butler, MD and Richard
W. Norman MD
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Blood in voided urine, or gross hematuria,
may be distressful for the patient and physician because even small
amounts can cause significant discolouration. Clots can impair drainage
from the kidney or bladder and produce pain. The bleeding can originate
from anywhere along the urinary tract and may indicate a serious
problem such as malignancy. Gross hematuria is a presenting symptom
of bladder cancer (85%) and renal cell carcinoma (40% of the time1,2).
On the other hand, urinary tract infections and stones are common
benign causes of gross hematuria.
Although clinically less impressive, microscopic
hematuria can be equally distressing to patients, and may stem from
any of the causes associated with gross hematuria. Both groups of
patients must be carefully evaluated to identify any significant
underlying disease.
There are varying definitions to describe
what constitutes significant microscopic hematuria. The Canadian
Urological Association (CUA) (www.cua.org)
defines it as more than two red blood cells (RBC) per high-power
field on two microscopic urinalyses collected without recent exercise,
menses, sexual activity or instrumentation.
How
is microscopic hematuria detected?
Urinary dipsticks are useful
for detecting microscopic hematuria and urologic pathology. Dipstick
testing has been shown to have a sensitivity between 91 and 100%,
but the specificity is more variable at 65-99%.3
As a result, false positives — sometimes as high as 16% —
may occur if myoglobin, free hemoglobin and oxidizing contaminants
(e.g. povidone-iodine) are present in the urine sample. Because
of the dipstick's limited specificity, it's essential to obtain
microscopic confirmation before proceeding with further investigation.
Urine microscopy involves centrifuging 10
mL of urine, collected as a freshly voided, clean-catch, mid-stream
sample, at 2,000 rotations per minute for five minutes. This is
followed by re-suspension of the sediment and examination under
a high-powered (x 400) microscope. Urine microscopy is a valuable
technique because it quantifies the evaluation and also allows the
clinician to differentiate the RBC qualities that may suggest a
glomerular cause of the hematuria.
Neither urinary dipsticks nor standard microscopy
are as quantitative or reproducible as the counting chamber technique,
where the number of RBCs per volume of urine excreted is calculated.
This method, however, isn't used as often because it's time-consuming.
Physicians should always consider microscopic
hematuria as a sign of an important underlying disease, until proven
otherwise. But despite its potential serious nature, hematuria may
occur without a definitive diagnosis. In five population-based studies,
the prevalence of microscopic hematuria varied between 0.19 and
6.1%.3
Differences in the age and gender of the participants investigated,
length of follow-up and the number of screening studies per patient
account for this range. In older men — who are at a higher
risk for significant urologic disease — the prevalence of asymptomatic
microscopic hematuria was as high as 21%.4-6
Further research into individuals over age 40 with asymptomatic
microscopic hematuria reveals an incidence of underlying bladder
or renal malignancy in up to 11% of patients. It's important to
evaluate those at greatest risk and ensure there's no serious underlying
pathology. For patients who are considered low risk for disease,
some components of the evaluation may be deferred.
 Trevor
J. Butler, MD, is Chief Resident of the Department of Urology at
Dalhousie University in Halifax.
Richard W. Norman MD, FRCSC is Chief of Urology at
the Queen Elizabeth II Health Sciences Centre, and Professor and
Head of the Department of Urology at Dalhousie University in Halifax.
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