Chapter 6. Laboratory Diagnosis: Urine Studies

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.

• 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

  • a. Neonates: 1.012

    b. Infants: 1.002–1.006

    c. Children and Adults: 1.001–1.035 (typical with normal fluid intake 1.016–1.022)

  3.  pH

  • a. Neonates: 5–7

    b. Children and Adults: 4.6–8.0

  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 crystals based on urine pH ...