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For routine urinalysis, a fresh (less than 1-h old), clean-catch
urine sample is acceptable. If the analysis cannot be performed
immediately, refrigerate the sample. (When urine stands at room temperature
for a long time, casts and red cells undergo lysis, and the urine
becomes alkalinized with precipitation of salts.) See Chapter 13, Urinary Tract Procedures, for sample collection.
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- 1. Pour 5–10 mL
of well-mixed urine into a centrifuge tube.
- 2. Check for appearance (color,
turbidity, odor). If a urine sample looks grossly cloudy, it is
sometimes advisable to examine an unspun sample. If you use an unspun
sample, make a note that you have done so. In general, a spun sample
is more desirable for routine urinalysis.
- 3. Spin the capped sample at
3000 rpm (450g) for 3–5 min.
- 4. While the sample is in the
centrifuge, use the dipstick (eg, Chemstrip) supplied by your lab
to perform the dipstick evaluation on the remaining sample. Read
the results according to the color chart on the bottle. Allow the
correct amount of time before reading the test (usually 1–2
min) to avoid false results. Chemstrip
10 provides 10 tests (specific gravity, pH, leukocytes, nitrite,
protein, glucose, ketone, urobilinogen, bilirubin, and blood.) Other
strips may provide less.) Agents that color the urine (phenazopyridine [Pyridium])
may interfere with the reading. Dipstick specific gravity (SG) measurement
is possible, but a refractometer also can be used to determine SG.
- 5. Decant and discard the supernatant.
Mix the remaining sediment by flicking it with a finger and pouring
or pipetting one or two drops onto a microscope slide. Cover with
a coverslip.
- 6. Examine 10 low-power fields
(10× objective) for epithelial cells,
casts, crystals, and mucus. Casts are usually reported as number
per low-power field and tend to collect around the periphery of
the coverslip.
- 7. Examine several high-power
fields (40× objective)
for epithelial cells, crystals, RBCs, WBCs, bacteria, and parasites
(trichomonads). RBCs, WBCs, and bacteria are usually reported as
number per high-power field. The following two reporting systems
are commonly used:
++
+
1.
Appearance: “Dark yellow
or amber in color and clear”
2.
Specific
Gravity
3.
pH
4.
Negative
for: Bilirubin, blood, acetone, glucose, protein, nitrite,
leukocyte esterase, reducing substances
5.
Trace: Urobilinogen
6.
RBC: Male
0–3/hpf, female 0–5/hpf
7.
WBC: 0–4/hpf
8.
Epithelial
Cells: Occasional
9.
Hyaline
Casts: Occasional
10.
Bacteria: None
11.
Crystals: Some
limited ...