Standard Operating Procedure: Routine Urine Examination

This Standard Operating Procedure (SOP) outlines the standardized process for performing a routine urine examination (urinalysis). The objective is to ensure accuracy, consistency, and clinical reliability in the physical, chemical, and microscopic evaluation of urine samples. Adherence to these protocols is mandatory for all laboratory personnel to minimize pre-analytical, analytical, and post-analytical errors.

Phase 1: Specimen Collection and Handling

• Patient Verification: Verify the patient’s identity against the laboratory request form.
• Collection Instructions: Ensure the patient provides a "clean-catch, mid-stream" urine specimen in a sterile, dry, leak-proof container.
• Labeling: Immediately label the container with the patient’s name, ID number, date, and time of collection.
• Transport: Transport samples to the laboratory within 1 hour of collection. If a delay is inevitable, refrigerate the specimen at 2°C to 8°C (do not freeze).
• Inspection: Check for container integrity, volume sufficiency (minimum 10mL recommended), and visible signs of contamination (e.g., feces, menstrual blood).

Phase 2: Physical Examination

• Color Assessment: Observe the urine against a white background. Note variations (e.g., straw, amber, red, brown).
• Appearance/Clarity: Evaluate the turbidity (clear, hazy, cloudy, or turbid).
• Volume: Note the total volume if a 24-hour collection is requested; otherwise, note the amount received.
• Odor: Record any unusual odors (e.g., fruity, foul, or ammoniacal) if clinically indicated or requested.

Phase 3: Chemical Examination (Reagent Strip Method)

• Preparation: Ensure the urine specimen is at room temperature and thoroughly mixed before testing.
• Dipstick Integrity: Check the expiration date of the reagent strips. Ensure the bottle is tightly capped.
• Immersion: Briefly dip the reagent strip into the urine, ensuring all pads are fully submerged.
• Drainage: Remove the strip and run the edge against the rim of the container to remove excess urine to prevent cross-contamination of chemical pads.
• Timing: Use a stopwatch to read the pads precisely at the manufacturer's recommended time intervals (usually 30–120 seconds).
• Reading: Compare the color changes against the bottle’s reference chart under adequate lighting.

Phase 4: Microscopic Examination

• Centrifugation: Transfer 10 mL of urine into a conical centrifuge tube. Centrifuge at 1500–2000 RPM for 5 minutes.
• Sediment Preparation: Decant the supernatant, leaving approximately 0.5–1 mL of urine with the sediment. Resuspend the sediment by gently tapping the tube.
• Slide Preparation: Place one drop of the sediment onto a glass slide and cover with a coverslip.
• Microscopy: Examine under 10x magnification for casts and crystals, and 40x magnification for RBCs, WBCs, bacteria, and epithelial cells.
• Reporting: Quantify findings per High Power Field (HPF) or Low Power Field (LPF) as established by laboratory protocol.

Pro Tips & Pitfalls

• Pitfall - Delayed Testing: Never test urine older than 2 hours without refrigeration; bacteria multiplication will alter pH and cause the breakdown of cells/casts.
• Pro Tip - Standardization: When performing microscopy, use the same volume of sediment and the same size coverslip for every patient to ensure consistency in quantification.
• Pitfall - The "Over-Dip": Do not leave the reagent strip in the urine too long, as this causes the reagents to leach out into the sample, resulting in false negatives.
• Pro Tip - Quality Control (QC): Always run positive and negative liquid controls daily before processing patient samples to ensure reagent strip validity.

Frequently Asked Questions (FAQ)

1. Why must the urine be mixed before analysis? Mixing is essential because formed elements, such as cells and crystals, settle to the bottom of the container over time. Failure to mix will result in an inaccurate, "falsely low" microscopic report.

2. What should I do if the urine is reddish-brown but the chemical dipstick for blood is negative? This indicates the presence of non-hemoglobin pigments, such as myoglobin, porphyrins, or intake of certain medications/foods (e.g., beets, rifampin). Consult the supervisor for further confirmatory testing.

3. Can I use a mid-stream specimen if the patient has just taken antibiotics? Yes, but you must note the current medication on the lab report, as antibiotics can inhibit bacterial growth in the culture and may occasionally interfere with chemical pad sensitivity.