A urine specimen can reach the bench already unfit to test: unlabeled, too small, in the wrong container, or changed by hours at room temperature. Preexamination errors can prevent patient identification or change urine composition before analysis. Container, volume, label, collection method, transport time, storage temperature, and preservative determine whether the laboratory can report a valid result.1,2
Container and volume
Routine urinalysis specimens are collected in wide-mouthed, flat-bottomed, clear containers with secure closures. These containers commonly have a capacity of approximately 50 mL. The minimum volume for microscopy comes from the laboratory's validated sediment method; a 12 mL aliquot is common. The submitted volume must also support all ordered tests and any repeat analysis. Screw caps are less likely to leak during transport than snap caps. Culture specimens require a sterile container. A nonsterile container makes the culture unacceptable even when the collection technique was otherwise adequate.2
Acceptability
The collector labels the container in the patient's presence at the time of collection. The label belongs on the container body because lids can be removed or exchanged. 2
Each laboratory defines its own specimen rejection criteria. Common reasons for rejection include:
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| Specimen defect | Laboratory consequence |
|---|---|
| Missing, illegible, or mismatched label | Patient identity cannot be verified, so the result cannot be assigned reliably |
| Visible fecal or tissue-paper contamination | Contaminants can alter chemical, microscopic, and culture results |
| Volume below the minimum for the ordered tests | The laboratory may be unable to complete the test order or repeat an analysis |
| Unpreserved specimen received after the laboratory's stability limit | pH, intact cells and casts, glucose, and bilirubin may no longer represent the collected urine |
| Culture specimen submitted in a nonsterile container | Environmental organisms can invalidate the culture; routine urinalysis may remain reportable |
| Collection method does not match the ordered test | Timed excretion or anatomic localization cannot be interpreted from the submitted specimen |
The collection method must also match the purpose of the test. A random specimen may suit routine urinalysis. It cannot measure 24-hour excretion.
Changes during storage
Urine begins to change after collection. Bacterial growth, oxidation, light exposure, loss of volatile compounds, and cell lysis alter chemical and microscopic findings in characteristic directions. A matching pattern can indicate a delayed or improperly stored specimen.
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| Measurement | Expected change after delay | Mechanism |
|---|---|---|
| pH | Increases | Bacterial conversion of urea to ammonia |
| Turbidity | Increases | Bacterial growth and crystal formation |
| Color | Darkens | Pigment oxidation |
| Glucose | Decreases | Cells and bacteria continue glycolysis |
| Ketones | Recovery decreases | Acetoacetate degrades and acetone volatilizes during storage |
| Bilirubin and urobilinogen | Decrease | Light causes photo-oxidation |
| Nitrite | Increases | Bacteria reduce nitrate to nitrite |
| Intact RBCs, WBCs, and casts | Decrease | Lysis, especially in dilute or alkaline urine |
A high pH, increased turbidity, positive nitrite, and loss of intact cells may occur together in a specimen that remained at room temperature for several hours.
College of American Pathologists (CAP) requirement URN.22300 directs CAP-accredited laboratories to examine urine within 2 hours of collection unless the specimen is refrigerated or chemically preserved.3
Refrigeration and preservatives
Refrigeration slows specimen deterioration without adding a chemical preservative. It can also precipitate amorphous urates and phosphates that obscure the sediment. Warming can redissolve urates. Under a validated procedure, dilute acid can be added to a separate aliquot to assess phosphate solubility. Do not acidify the aliquot reserved for routine chemistry or microscopy because acid changes pH, alters particles, and lyses red cells. Neither warming nor acid treatment reliably restores an uninterpretable preparation. Request a fresh specimen when precipitate prevents particle identification.
No single preservative is compatible with every urine test. Select the preservative for the ordered analysis before transport because it cannot be removed after addition. Boric-acid transport systems maintain bacterial counts for culture. Hydrochloric acid is used for selected quantitative chemistry collections and is unsuitable for culture.1,2 Fill fixed-dose boric-acid tubes to the volume the device specifies. Underfilling raises the preservative concentration and can inhibit organisms, producing a falsely low or negative culture. Follow the device instructions and the laboratory's specimen-acceptability policy.4
Practice
References
- Kouri TT, Hofmann W, Falbo R, et al. The EFLM European urinalysis guideline 2023. Clin Chem Lab Med. 2024;62(9):1653-1786. doi:10.1515/cclm-2024-0070 Back to text
- Clinical and Laboratory Standards Institute. Processes for the Collection of Urine Specimens. 1st ed. CLSI guideline PRE05. Clinical and Laboratory Standards Institute; 2024. Accessed August 27, 2026. https://clsi.org/shop/standards/pre05/ Back to text
- College of American Pathologists. Urinalysis Checklist. December 9, 2025 ed. Requirements URN.22300 and URN.22400. Applies to CAP-accredited laboratories. CAP accreditation checklists. Back to text
- UK Health Security Agency. Diagnosis of urinary tract infections: quick reference tools for primary care. Updated July 7, 2025. Accessed August 29, 2026. Back to text