© The Canadian Journal of Urology™; 19(Supplement 1); October 2012
37
What is significant hematuria for the primary care physician?
the patient’s clinical history confirms the presence of
hematuria, further questions may localize the source
of bleeding. If gross hematuria appears throughout
the urinary stream, then it probably originates above
the level of the bladder outlet, including the upper
urinary tract and kidneys. If blood is detected only
at the initiation of urination, then it is likely from
the urethra. Gross hematuria at the end of urination
may be from the prostate or bladder neck. Taking an
inventory of associated symptoms may help generate a
differential diagnosis. For example, flank pain, nausea,
and hematuria suggest a renal colic attack. Pain, mass,
and hematuria use to be considered the classic triad
for the suspicion of renal cell cancer. However, today
most cancers are found serendipitously at the time of
an abdominal ultrasound.
2
Even if further details are
missing, the presence of gross hematuria necessitates
further evaluation and/or referral to a specialist.
Microscopic hematuria is a more common finding
than gross hematuria. The reason for significant
microscopic hematuria can be more difficult to
determine. Microscopic hematuria is often detected
from a positive urine dipstick test. Although a dipstick
test is a convenient, rapid, point-of-care test, it has
pitfalls. Dipsticks are based on a chemical reaction
between the dipstick reagent and substances in the
urine that produces a color change. The color change
can be affected by factors affecting the dipstick reagent,
urine, or their interaction. Therefore, microscopic
urinalysis is recommended to confirm a positive
dipstick test for hematuria.
3
Inmicroscopic urinalysis,
urine is centrifuged, most of the supernatant is
poured off, and the sediment is re-suspended in the
residual supernatant. The sediment aliquot is then
examined under a microscope, using low- and high-
power magnification. Microscopic urinalysis is more
laborious than dipstick testing and was traditionally
performedmanually. More recently, this procedure has
been automated to make it more rapid, reproducible,
and accurate.
4
In the Canadian guidelines, significant microscopic
hematuria is defined as 2 ormore red blood cells (RBCs)
per high power field, confirmed in two microscopic
urinalysis tests performed when there is no benign
etiology such as menstruation, recent exercise, recent
sexual activity, or recent instrumentation of the
urinary tract.
5
T heAmerican recommendations define
significant microscopic hematuria as 3 or more RBCs
per high power field in a properly collected specimen
and in the absence of a benign etiology.
6
Physicians
should make sure to use a consistent definition for
significant microscopic hematuria.
Causes of significant hematuria
The identification of significant hematuria may trigger
anxiety in patients and they may ask physicians
about potential reasons for this finding. Primary care
physicians need a working knowledge of the main
etiologies of significant hematuria. They also need
to consider initiating further investigations and, if
needed, make a referral to a specialist.
Urinary tract infection
Microscopic hematuria is usually associated with
urinary tract infections (UTIs) and can even cause gross
hematuria, although this is less common. Patients with
a UTI generally also have other voiding symptoms,
especially dysuria and acute urinary frequency. It
is important to remember that finding symptomatic
hematuria and a positive urine culture in a patient
should not always pre-empt the need for looking for
other potential causes of the hematuria. However,
referral to a urologist may generally be delayed when
the patient has a positive urine culture. Treatment of
the infection and repeat assessment of the urine should
be conducted in this setting.
Urolithiasis
Kidney stones are common and both men and women
mayhave them. They are a clinical problemthat appears
to be increasing in prevalence, requiringmore sustained
efforts in diagnosis, treatment, and prevention.
7
TABLE 1.
Common causes of red urine
2
With a positive dipstick for blood
•
Hematuria
•
Hemoglobinuria
•
Myoglobinuria
•
Menstrual contamination
With a negative dipstick for blood
Foods
•
Beets
•
Berries
•
Food coloring
Drugs
•
Aminosalicylic acid
•
Ibuprofen
•
Laxatives containing phenolphthalein or senna
•
Methyldopa
•
Phenazopyridine
•
Phenothiazines
•
Rifampin
