Before you interpret a urine result, check how and when the specimen was collected. The collection method determines the concentration of the specimen, the portion of the urinary tract represented, and the risk of contamination. Interpret every result with the specimen type and collection time.1,2
Routine collections
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| Specimen | Collection method and principal use | Interpretation and quality concern |
|---|---|---|
| Random | Voided at any time without a specified interval or relation to the previous void. Used for routine urinalysis and screening when collection time is not critical. | Hydration and time of collection are not standardized, so analyte concentrations can differ substantially between specimens. |
| First morning | The first void passed immediately after waking, following overnight bladder retention. Its concentrated composition supports detection of low-concentration constituents, early pregnancy testing, and evaluation of orthostatic proteinuria (protein excretion that appears with upright posture and clears when recumbent). | A later void is not equivalent because it may be less concentrated and no longer represents the recumbent overnight interval. |
| Timed (24-hour) | All urine produced during an exact 24-hour interval, with the start-time void discarded and the end-time void included. Used to measure total daily excretion of analytes such as catecholamines, steroids, electrolytes, and protein. | A missed void produces a falsely low excretion result; including urine formed outside the interval produces a falsely high result. |
| Midstream clean-catch | The patient passes the initial stream into the toilet and collects the middle portion. Used for routine urinalysis and culture with reduced urethral and genital contamination. | Collecting the initial stream or allowing contact with skin can introduce flora and produce a misleading culture result. |
| Catheterized | Bladder urine is obtained through a urethral catheter. Used for culture or urinalysis when an adequate voided specimen cannot be obtained; contamination from the external genitalia is reduced. | Catheterization is invasive, can introduce infection, and can cause urethral trauma. |
| Suprapubic aspiration | Urine is withdrawn directly from the bladder through a needle inserted above the pubic bone. Used for culture and cytology when urethral contamination must be avoided. | The procedure is invasive and is reserved for selected situations in which its diagnostic value justifies bladder puncture. |
| Pediatric bag | Voided urine is collected in an adhesive bag placed over the external genitalia. Used for screening urinalysis in infants who cannot provide a clean-catch specimen. | Perineal flora frequently contaminate the specimen; a positive bag culture cannot establish a urinary tract infection. |
A pediatric bag specimen can be used for screening urinalysis. It is unsuitable for diagnostic culture because perineal contamination can produce bacterial growth from outside the urinary tract. A bag culture with no bacterial growth lowers the likelihood of urinary tract infection. It does not exclude infection. When a bag culture grows bacteria, request a new specimen collected by catheterization or suprapubic aspiration for diagnostic culture. 2
Timed collections
A 24-hour collection measures total analyte excretion during a defined interval. Accurate results depend on collecting every void and maintaining an interval of exactly 24 hours. 2
Before the start time, obtain the container, preservative, storage conditions, and collection instructions specified by the performing laboratory. Some analytes require a preservative from the beginning of collection, and one preservative is not suitable for every test. Do not add or change a preservative unless the laboratory instructions permit it.2
- At the start time, empty the bladder and discard the urine. This urine was produced before the collection interval began.
- Save every void produced during the next 24 hours.
- At the end of the 24-hour interval, empty the bladder and keep this final urine.
- Mix the complete collection, measure and record the total volume, and then remove an aliquot for testing.
Including the initial void adds urine produced before the collection interval and may falsely increase the calculated excretion. Omitting any void, including the final one, produces an incomplete collection and may falsely decrease the result. The laboratory usually cannot detect either error from the aliquot alone.
Midstream clean-catch
During a midstream clean-catch collection, the initial urine stream flushes urethral flora before the specimen is collected. The patient keeps only the midstream portion.
When the local procedure includes genital cleansing, water is generally sufficient. Soap or antiseptic carried into the specimen can inhibit bacterial growth and produce a false-negative culture.2
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