Standard Operating Procedure: Clinical Urinalysis

This Standard Operating Procedure (SOP) outlines the standardized process for performing a comprehensive urinalysis, including physical, chemical, and microscopic examination. Adherence to this protocol is critical to ensure analytical accuracy, maintain laboratory safety, and prevent diagnostic errors resulting from improper specimen handling or testing techniques. All personnel must strictly follow Universal Precautions when handling biological specimens.

I. Pre-Analytical Preparation

• Verify patient identification (two-factor check: full name and date of birth).
• Ensure the specimen is labeled correctly with date, time, and patient ID.
• Confirm the specimen was collected in a clean, sterile, leak-proof container.
• Assess specimen integrity: reject samples that are contaminated with feces, toilet paper, or those older than two hours (if not refrigerated).
• Don appropriate Personal Protective Equipment (PPE), including gloves, lab coat, and eye protection.

II. Physical Examination

• Color Assessment: Observe the specimen against a white background. Record findings (e.g., pale yellow, amber, red, brown).
• Clarity/Turbidity: Hold the container against a light source. Categorize as clear, hazy, cloudy, or turbid.
• Specific Gravity: Calibrate the refractometer using distilled water (target 1.000). Apply a drop of urine to the prism and record the reading.

III. Chemical Examination (Reagent Strip Method)

• Ensure reagent strips are within the expiration date and have been stored away from moisture/light.
• Mix the urine specimen gently but thoroughly by swirling.
• Dip the reagent strip briefly into the urine, ensuring all pads are fully submerged.
• Remove the strip and drag the edge against the rim of the container to remove excess urine.
• Hold the strip horizontally to prevent cross-contamination of reagents.
• Compare pad colors against the manufacturer’s color chart at the exact time intervals specified on the bottle label.
• Record results immediately in the Laboratory Information System (LIS).

IV. Microscopic Examination (If Indicated)

• Transfer 10–12 mL of urine to a standardized conical centrifuge tube.
• Centrifuge at 1500–2000 RPM for 5 minutes.
• Decant the supernatant, leaving approximately 0.5–1.0 mL of urine at the bottom.
• Resuspend the sediment by gently flicking the tube.
• Transfer one drop of sediment to a microscope slide and apply a coverslip.
• Examine under low power (10x) to screen for casts and crystals; examine under high power (40x) to identify cells, bacteria, and yeast.

V. Post-Analytical Procedures

• Dispose of all biohazardous waste in designated containers.
• Disinfect the workspace using a 10% bleach solution or hospital-grade disinfectant.
• Remove PPE and perform thorough hand hygiene.
• Verify that all results have been correctly entered and flagged for abnormal values.

Pro Tips & Pitfalls

• Pro Tip: Always perform chemical testing before centrifuging. Centrifugation can alter the physical distribution of cells and debris, potentially affecting chemical readouts if samples are mixed improperly afterward.
• Pitfall - Timing: Do not wait too long to read the reagent strips. Colors may deepen after the prescribed time, leading to false-positive results, particularly for leukocytes and nitrites.
• Pitfall - Temperature: Ensure the specimen has reached room temperature before testing. Cold urine can slow the chemical reaction on the reagent strip and decrease specific gravity accuracy.

Frequently Asked Questions (FAQ)

Q: Can I use an old specimen if it was kept in the refrigerator? A: Refrigerated specimens are acceptable if processed within 24 hours. However, ensure the sample is allowed to return to room temperature and is mixed well before testing to ensure crystals are properly resuspended.

Q: What should I do if the urine color is abnormal (e.g., bright red or dark brown)? A: Note the visual appearance in the comments section. If the reagent strip shows blood but the microscopy is negative for RBCs, investigate the presence of myoglobin or hemoglobin, or consider patient medication interference.

Q: How do I handle a "QNS" (Quantity Not Sufficient) specimen? A: If the volume is insufficient for all requested tests, prioritize the chemical dipstick and microscopic exam. Document the specific volume received and mark the report as "QNS" for any tests that could not be completed.