Chapter 1 · Urine specimen collection and integrity

Urine specimen integrity is highly dependent on collection conditions. A mid-stream urine (MSU) requires patient preparation instructions, which must be documented and provided. Specimens must be processed within 2 hours of collection at room temperature, or refrigerated at 4°C for up to 24 hours. Delay causes: bacterial multiplication (falsely elevated counts), cellular lysis, and cast dissolution. Specimens received without a documented collection time must be questioned.

Chapter 1 · Practical example

Specimen collection — the 2-hour rule and its consequences

Urine must be analysed within 2 hours of collection at room temperature. Delayed samples undergo bacterial multiplication and cellular deterioration that invalidate results.

▲ The situation

A urine sample arrives in the laboratory at 16:30. The collection time documented on the tube is 09:15 — over seven hours ago. There is no refrigeration label.

Reference: ISO 15189:2022 Clause 7.2.6; PHE Urine Specimen Processing Guidelines

✓
Good practice

The analyst checks the transit time — 7 hours 15 minutes at unknown temperature, no documentation of refrigeration. She rejects the sample: transit time exceeds 2-hour room temperature limit and refrigeration cannot be confirmed. She contacts the requesting ward explaining that bacteria multiply in urine at room temperature, making microscopy, culture results, and dipstick leucocyte findings unreliable. Recollection is requested with immediate transport or documentation of cold chain.

✗
Poor practice

The sample is processed. Dipstick: LE 3+, nitrite positive. Culture the following day: heavy growth E. coli. A UTI is diagnosed and antibiotics prescribed. The growth may represent bacterial multiplication during seven hours at room temperature rather than true bacteriuria. The patient receives treatment they may not need. The specimen quality was never assessed.

● What this means for your practice

Collection time is not administrative metadata — it is a pre-analytical quality parameter. Check it at receipt for every urine sample. A rejected sample with a clear explanation is always preferable to a result that may be entirely artefactual.