CLINICAL LAB SCIENEC

CHAPTER 12: PROCEDURES FOR URINALYSIS AND BODY FLUIDS 315
3. Fresh urine sample that has tested positive for protein by dipstick
(see Procedure #1)
4. Disposable dropper pipettes such as Pasteur or disposable bulb
pipettes
5. Deionized or distilled water
6. Centrifuge and centrifuge tubes
7. Normal and abnormal urine controls (see following note)
Some urine controls contain different levels of protein, such as a
low level for normal controls and a high level for abnormal controls.
These levels can be then be graded as either negative or 1– 4+. If
the controls are not suitable for this procedure, semiquantitative
controls can be made by using a sample of protein that may be
obtained from serum and that is diluted to obtain various amounts of
protein, from a low level to a high level.
8. 13 × 100 mm test tubes and test tube rack
9. Trichloroacetic acid (TCA) or sulfosalicylic acid (SSA)
10. Black background (helpful for observing the whitecolored
turbidity that results from a positive reaction as the
precipitate is white)
11. Electronic timing device or clock/watch with second hand
Procedure
• High specifi c gravity
1. Wash hands and don gloves.
• Loss of reagent strip buffer by
2. Assemble necessary equipment and supplies.
increased contact with specimen
3. Pour 5 mL of urine sample into a disposable centrifuge tube (Figure
12-13).
4. Centrifuge tubes for 5 minutes at 400 RCF. This removes cellular components
and other solid substances that may affect the turbidity of a positive test result.
5. Separate the supernatant from the sediment by use of a serological or other
mechanical pipette, placing 2 mL of the supernatant into a 13 × 100 mm test tube.
6. Add 2 mL SSA or TCA and mix thoroughly. Exercise care in handling SSA, as it
can be caustic if it comes into contact with the skin.
7. After 10 minutes, observe for the amount of turbidity using the following scale.
Negative No turbidity (clear)
Trace Barely visible turbidity
1+ Noticeable turbidity
2+ Significant turbidity with granulation
3+ Granulation with clumps
4+ Completely opaque and chiefly clumps
8. Discard all supplies used for the procedure in the appropriate containers. A disinfectant
should be used to clean the work surfaces and equipment should be
cleaned and restored to its former position. Gloves should be discarded appropriately
and the hands washed thoroughly in accordance with established policies.
Critical Reminders
False Positives
The false positive paradox is
a situation where the incidence of
a condition is lower than the false
positive rate of a test and therefore
when the test shows that a condition
exists, it is probable that the result is
a false positive.
Conditions That May Lead to a
False Positive Test for Urinary
Protein by Dipstick
• Highly alkaline urine samples
• Some pigmented (colored)
medications
• Disinfectants (quaternary
ammonium compounds)
• Antiseptics such as chlorhexidine
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