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7. Examination of urine 239
The analytical range of this modified method is 25–700mg/l.
Protein in urine can also be detected using a protein dipstick (see section 7.2.2).
7.2.6 Detection of ketone bodies
Normal urine does not contain ketone bodies. Acetone and other ketone bodies
may appear in urine:
— in severe or untreated diabetes;
— in certain other conditions (dehydration, vomiting, malnutrition, prolonged
starvation and following strenuous exercise).
Principle
When sodium nitroprusside (sodium nitrosyl pentacyanoferrate (III)) is added to
urine containing ketone bodies, a purple colour is produced.
Materials and reagents
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Test-tubes
Test-tube rack
Measuring cylinder, 10ml
Dropping pipette
Sodium nitroprusside crystals
Acetic acid
Ammonia.
Method
1. Just before carrying out the test, place a sufficient number of sodium nitroprusside
crystals into a test-tube to cover the bottom (Fig. 7.6).
2. Add 5ml of distilled water. Shake well until the crystals are almost dissolved.
(Not all the crystals are expected to dissolve as the solution is saturated.)
3. Measure 10ml of urine into another test-tube.
4. Add four drops of acetic acid to the urine, followed by 10 drops of freshly prepared
sodium nitroprusside solution. Mix well.
5. Holding the tip of the pipette against the side of the tube, let 20 drops (1ml) of
ammonia solution flow on to the surface of the liquid (Fig. 7.7). Wait for 5 minutes
before reading — a positive result may be obvious before this time.
Fig. 7.6 Preparation of sodium nitroprusside solution
Fig. 7.7 Adding ammonia solution to the
surface of the sodium nitroprusside
solution