Specimen Collection and Handling
Urine Specimen Types
How to select and evaluate routine urine specimen types, including timed and midstream collections.
Urine specimen types are not interchangeable. Each collection method answers a different clinical question and has its own sources of error. Results must therefore be interpreted according to the type of specimen submitted.
Routine collections
| Specimen | What it answers | What limits it |
|---|---|---|
| Random | Routine screening | Least standardized; concentration varies with fluid intake |
| First morning | Tests requiring a concentrated specimen, such as early pregnancy testing or evaluation of orthostatic proteinuria | Must be collected immediately after waking |
| Timed (24-hour) | Excretion of analytes that varies during the day, such as catecholamines, steroids, and electrolytes | Requires collection of every void during the timed interval |
| Midstream clean-catch | Routine screening and culture | Quality depends on collection technique |
| Catheterized | Bladder urine with less contamination | Invasive and carries a risk of infection |
| Suprapubic aspiration | Culture and cytology without urethral contamination | Invasive and limited to selected clinical situations |
| Pediatric bag | Screening in infants | High contamination rate; a positive culture is not diagnostic |
Pediatric bag specimens require particular caution when culture results are interpreted. Contamination is common, so a positive culture from a bag specimen cannot establish a urinary tract infection. Diagnostic culture in an infant requires a catheterized specimen or suprapubic aspirate. A negative bag culture can help exclude infection, whereas a positive result must be confirmed using one of these more reliable collection methods.
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.
- 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.
Worked example. A 24-hour urine protein result is much lower than the previous result from the same patient, and the recorded volume is 700 mL. In an adult who is not fluid-restricted, this low volume raises concern for an incomplete collection. Collection completeness should be evaluated before an analytical problem is suspected.
Midstream clean-catch
During a midstream clean-catch collection, the initial urine stream flushes urethral flora before the specimen is collected. Only the midstream portion is retained.
When genital cleansing is included in the local procedure, water is generally sufficient. Soaps and antiseptics should be avoided because carryover into the specimen can inhibit the organisms that culture is intended to detect.
References
- Kouri TT, Hofmann W, Falbo R, et al. The EFLM European Urinalysis Guideline 2023. Clin Chem Lab Med. 2024;62(9):1653-1786.
- Clinical and Laboratory Standards Institute. Processes for the Collection of Urine Specimens. 1st ed. CLSI guideline PRE05. CLSI; 2024.