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7. Examination of urine 241
Method
Collection of specimens
Urine to be examined under the microscope must be freshly passed into a clean dry
vessel. A midstream urine specimen (see section 7.1.1) is the most useful. Urine
stored in a refrigerator may contain an excess of precipitated salts and will not be
suitable for microscopy.
The specimen can be preserved for microscopic examination of the deposit by
adding 8–10 drops of formaldehyde, 10% solution (reagent no. 28) per 300ml of
urine. Urine preserved in this way is not suitable for other tests.
Preparation of the deposit
1. Mix the urine specimen gently and pour approximately 11ml into a centrifuge
tube.
2. Centrifuge the specimen at medium speed (2000g) for 5 minutes.
3. Pour off the supernatant by quickly inverting the tube without shaking. (The
supernatant may be used for biochemical testing.)
4. Resuspend the deposit in distilled water and mix by shaking the tube.
5. Transfer one drop of the deposit on to a slide using a Pasteur pipette and cover
with a coverslip.
6. Label the slide with the patient’s name or identification number.
Microscopic examination
Using the ¥ 10 objective and with the condenser lowered, scan the coverslip all over
to look for ova of Schistosoma haematobium when indicated.
Using the ¥ 40 objective and with the condenser lowered or aperture reduced, scan
the coverslip area again and report any findings as a quantitative value for each
high-power field.
The following may be found in urine:
— erythrocytes
— leukocytes
— epithelial cells
— casts
— fungi
— crystals
— parasite eggs and larvae
— Trichomonas vaginalis
— spermatozoa.
Erythrocytes (Fig. 7.9)
Erythrocytes in urine may be:
(a) intact: small yellowish discs, darker at the edges (8mm);
(b) crenated: spiky edges, reduced diameter (5–6mm);
(c) swollen: thin circles, increased diameter (9–10mm).
The shape of the cells often changes during storage of urine
and does not have any diagnostic importance.
There are normally very few erythrocytes in urine.
Fig. 7.9 Erythrocytes
a: Intact cells; b: crenated cells; c: swollen
cells.