Urine Sediment Microscopy-2

Particles of the urinary sediment :-
In the urine sediment we can find cells, lipids, casts, crystals and microorganisms.

We have two groups of cells in the urinary sediment: the cells deriving from blood and the cells of epithelial origin. The cells deriving from blood include: erythrocytes, leukocytes, and macrophages. The epithelial cells include: renal tubular cells, transitional cells, and squamous cells.

Erythrocytes:- in the urine we can find two main types of erythrocytes: the so-called glomerular (or dysmorphic) erythrocytes and the so-called non-glomerular (or isomorphic) erythrocytes.

These are cells with irregular shape, size, and cell membrane, which differ remarkably from the image of erythrocytes we have stored in our mind.

Non glomerular or isomorphic erythrocytes i.e., erythrocytes with a spherical shape and regular contours, containing (green-bluish cells) or not (colourless cells) haemoglobin.

What is the clinical implication of distinguishing glomerular from non glomerular erythrocytes?
glomerular or dysmorphic erythrocytes were found in patients with haematuria caused by a glomerular disease, while non glomerular or isomorphic erythrocytes were found only in patients with hematuria of urological origin. Thus, it was concluded that the evaluation of urinary erythrocyte morphology could be used to identify the source of hematuria.

However, the evaluation of the urinary erythrocyte morphology is associated with some drawbacks. First of all it requires experience. Then, it is exposed to the risk of a low inter-observer reproducibility. In fact, there are investigators who consider a haematuria as glomerular when 2 erythrocyte subtypes are present, others who say that there must be at least 3 subtypes of erythrocytes, while others as we have just seen use a >80% cut-off, others use other cut-offs, etc.

Köhler and co-workers showed that there is a subtype of dysmorphic erythrocyte, which they called “acanthocyte”, which can be easily (and less subjectively) identified due to its shape of a ring from which one or more blebs protrude (slide shown below shows an acanthocyte as seen by scanning electron microscopy) and which they found to be a marker of glomerular bleeding.




the slide below shows acanthocyes on phase contrast microscope.





What is the main indication for the evaluation of urinary erythrocyte morphology in clinical practice?
It’s persistent isolated microscopic haematuria of unknown origin In this condition, the evaluation of red cell morphology helps in deciding whether the patient has to be submitted to a nephrological work-up rather than to a urological one. This saves to the patient inappropriate investigation such as cystoscopy for a patient with haematuria due to a glomerular disease.

Urine Sediment Microscopy

The urinary sediment was introduced into clinical practice in the late 1830s in Paris at La Charité hospital by François Rayer and his pupil Eugène Napoléon Vigla. By the end of the 19th century, all the main particles had been identified and the main urine profiles had been described. However, in the subsequent century, the 20th century, the urinary sediment examination knew only a progressive decline with only very few exceptions. One was the original and important work of Thomas Addis in the 1920s and the other was the publication, in 1982, of a paper by Fairley and Birch on the utility of urinary erythrocyte morphology evaluation by phase contrast microscopy in patients with hematuria.

Methodological 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.

Collection of the urine:-

According to the strategy of the single lab, we can ask the patient to supply the first or the second urine of the morning. Usually ask for the second urine, since overnight urine, due to its prolonged permanence in the bladder can favour the lysis of particles. Advise 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). Also advise the patient to clean the external genitalia in an ordinary way. 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, 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 5 cm to allow easy collection of urine for both men and women, a wide base to avoid accidental spillage, a cap to avoid leakage, a label for patient identification).

Standarized method for handling of urine sample:-

What 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. Ask the patient to supply the second urine of the morning produced over a period of 2 hours; then, centrifuge a 10 mL aliquot of urine for 10 minutes at 400 G , which correspond to 2,000rpm . Then, remove with a pump a fixed volume of supernatant urine, which is 9.5 mL. Then, with a Pasteur pipette, gently but thoroughly re-suspend the sediment in the remaining 0.5 mL of urine. Then, with a precision pipette, transfer 50 mL of resuspended urine to a glass slide, which is covered with a coverslip of a fixed surface, namely 32 x 24 mm . Then, examine the samples at low and high magnification (160x and 400x) within 3 hours from urine collection. For routine practice, express the particles as lowest/highest number seen by microscopic field.

Various findings on urine microscopy:-

To know how the various Casts and Crystals appear on microscopy, download the file showing the pictures of common findings of urine microscopy. Click the link below to download the file.

urine microscopy showing common casts and crystals