BEDSIDE URINARY MICROSCOPY
GIOVANNI BATTISTA FOGAZZI LECTURES SERIES
URINARY SEDIMENT: Part 1: Methods
G.B. Fogazzi, Milan, Italy
Dr G.B Fogazzi
Research Laboratory on Urine, Unità Operativa di Nefrologia
Fondazione IRCCS, Ospedale Maggiore Policlinico, Mangiagalli e Regina Elena
Prof Fogazzi: This is the outline of the course. After a brief introduction, I will speak about the main methodological aspects concerning the urinary sediment; the particles of the urinary sediment of nephrological importance with their clinical implications; the urinary sediment in the clinical practice and, finally, I will draw some conclusions.
the historical point of view, we know that the urinary sediment was introduced
into clinical practice in the late 1830s in
What is the situation today? In most instances, urinary sediments are examined in central laboratories far from bedside and without the correct equipment and knowledge, and with the dream to entrust the whole task to automated instruments. These are already on the market, one being UF 100, which is based on flow cytometry, and the other iQ200, which is based on images obtained by a video camera. Last but not least, too often the urinary sediment examination is neglected even by nephrologists.
our unit at the Ospedale Maggiore of
aspects are very important for urine sediment. The main methodological aspects
include: a correct urine collection; a standardised method for the handling of
the urine; the use of a proper microscope and the use of a proper report to
describe the findings. All these aspects are described in detail in the
document published by the European Urinalysis Group 5 years ago as a supplement
of the Scandinavian Journal of Clinical and Laboratory Investigation (2000; Vol
60, Suppl 231) as well as in our book (Fogazzi GB, Ponticelli C, Ritz E. The
Urinary Sediment. An Integrated View 2nd Edition.
to urine collection, it’s important to give the patient written and simple
instructions. According to the strategy of the single lab, we can ask the
patient to supply the first or the second urine of the morning. In our lab, we
ask for the second urine, since
overnight urine, due to its prolonged permanence in the bladder can favour the
lysis of particles. We suggest the patient to avoid strenuous physical effort
in the hours preceding the test, since this may influence in various ways the
findings (for instance by causing haematuria and/or cylindruria). We advise the
patient to clean the external genitalia in an ordinary way. In this respect, we
do not suggest special procedures
since the more the procedures
suggested are complicated, the less the patient is compliant. In order to avoid
contamination, the male has to uncover the glans and female to spread the labia
of the vagina. For the same reason, we always suggest to collect midstream
urine. It’s important to remember that urine collection during menstruation must
be avoided because of the high probability of blood contamination. It is
also important to use a proper urine container (with a capacity of at least 50
to 100 mL, an opening of at least of
about a standardized method for the handling of urine? Why is standardization of
the handling of the urine important? It is important because only with a
standardized method we can obtain quantitative reproducible results. The slide
shows the method that we use in our lab. We ask the patient to supply the
second urine of the morning produced over a period of 2 hours; then, we
centrifuge a 10 mL aliquot of urine for 10 minutes at
And now the microscope. The microscope must be of good quality, must be equipped with a low and high magnification, and must, and I want to stress must, be equipped with phase contrast and polarized light.
This is the microscope we use in our lab. Why phase contrast?
It’s very simple to explain. On the right you see bright-field, and on the left you see phase contrast. You see that with phase contrast the particles are much better seen against the background than with bright-field, and this without the use of stains! I want to stress that the European Guidelines strongly recommends the use of phase contrast microscopy.
And why polarized light? Polarized light is extremely useful to correctly recognize the crystals. For example, you see uric acid crystals as seen by phase contrast microscopy (slide 15), and what happens when we use polarized light (slide 16). Under polarized light, uric acid crystals assume a typical polychromatic appearance, which is useful to identify them.
Polarized light is also important to correctly identify lipid particles,
which under polarized light appear as “Maltese crosses” which is, “shining” particles containing a “black cross” whose arms are regular and symmetrical. This feature allows the identification of lipid particles, especially when they come with an atypical appearance.
Now, the urinary sediment report. This is the report we use in our lab. After the patient details, we have pH, density (or specific gravity), haemoglobin and leukocyte esterase as detected by dipstick. Then the particles: erythrocytes (with their morphological classification; see below), leukocytes, tubular cells, transitional cells (from the deep and superficial layers of the uroepithelium), squamous cells, casts, lipids, crystals, bacteria, and yeasts. We also have a space for a brief conclusive comment. I want to stress the importance of having in the report the findings obtained by dipstick. Why this?
Let me give you an example. You see in this slide a sample with a pH of 6.0, a density of 1.006, a +++ haemoglobin and +++ leukocyte esterase by dipstick. However, by microscopy we find a low number of erythrocytes and leukocytes, which is in contrast with +++ haemoglobin and +++ leukocytes esterase. Is there any explanation for this discrepancy? Yes there is. The discrepancy is due to the fact that low density causes the lysis of erythrocytes and leukocytes, which therefore cannot be seen by microscopy. In contrast, in other instances we may have negative haemoglobin and many erythrocytes by microscopy. This may be due, for example, to the presence of large concentrations of Vitamin C in the urine, which reduces the sensitivity of dipstick for haemoglobin. Therefore, it is always important to match the findings obtained by dipstick with those obtained with microscopy and to try to explain them. Thus, our comment for the sample shown in the slide is: ” Mild erythrocyturia and leucocyturia. Please note the discrepancy between dipstick for haemoglobin and leukocyte esterase and microscopy. This is probably due to cell lysis caused by low density.” The final message on this point is that examining the urine only by dipsticks or only by microscopy exposes to the risk of false results. This risk is reduced when both methods are used on the same sample.
THE SECOND PART WILL BE PUBLISHED ON SEPTEMBER 28TH