Urine
(Microbiology)

Although these are by far the commonest sample sent to the laboratory, they seem to attract the least attention to detail. About one quarter of requests are either obviously contaminated (judging from the presence of vulvo-vaginal squamous epithelial cells in the urine) or arrive in the laboratory the day after the specimen was passed by the patient. Up to half the requests from wards have no relevant clinical information to indicate why the sample has been sent. And 15 to 20% of them have significant antibacterial activity present without any pointers to this possibility being noted on the request form. The great majority of 'sterile pyurias' can be attributed either to pseudo-pyuria of vulvo-vaginal origin or to antibiotic therapy.

In the female, introital cleansing is the most important determinant of a 'clean' specimen. Collection can usually be deferred until immediately after the patient has showered or bathed. Among bed-bound patients the risk of contamination is considerably greater so all the more attention should be paid to the simple expediency of perineal and introital cleansing; the mid-stream aspect then becomes much less important. Only soap and water, never disinfectants, should be used for cleansing. 'Dip-stick' tests for glucose, protein, blood, etc. are not routinely performed on urine samples submitted for microbiological tests because such screening has usually already been done on the ward, or in the clinic or surgery. Such tests will be undertaken if the request form clearly indicates that this is required.

NB. If a freshly passed urine is found outside the laboratory to have an alkaline pH a note of this should be recorded. An alkaline reaction is a sine qua non for Proteus infections, whereas contamination with this organism during collection will not alter the normally acidic pH of the urine as long as this is tested immediately.

NB. EMUs (Early Morning Urine for TB studies) is discussed under the specific heading in the index.

Catheter samples (CSU)
Closed drainage systems should not be 'broken' for the purpose of obtaining a sample, which should be aspirated using a sterile syringe and needle inserted aseptically into the sampling port on the catheter tubing. Urine from drainage bags is not representative of the urine draining from the bladder. Microscopy is not routinely performed on CSUs unless there is a specific request to do so : the presence or absence of pyuria is of no predictive value for infection when a catheter is in situ.

NB. It is not worth sending the tips of bladder catheters for culture after removal. Submission of an MSU 48-72 hours later is far more informative.

Ileal conduit samples and nephrostomy tube samples
These will have a microscopy performed if the nature of the sample is clearly marked on the request form (rather than simply suggesting that they are 'CSUs' without further qualification). In both cases urine from drainage bags is liable to be misleading in terms of culture results.


Investigation Microscopy
Culture and sensitivity
Inform lab before sending No (unless urgent)
Specimen type Mid-stream urine (MSU)
Supra-pubic aspirate
Bag urine
Ileal conduit urine
Nephrostomy urine
Urostomy urine
Ideal time to take speciemn Before antibiotic therapy
Specimen container Sterile leak proof container (see above)
Labelling requirements click here
How to take specimen See above
Volume 5 - 10ml
Transport to the laboratory If transport is delayed then refigerate sample. Delays of over 48 hours are undesirable
Turnround Negative urines <24 hours,
Positive urines 24 - 48 hours
Additional information Any samples suspected of containing organisms belonging to hazard group 3 (e.g. TB) should be clearly marked as such on the request form.

Biochemical dipstick tests are not performed in the Microbiology laboratory as such tests are usually performed as near patient testing.
Specimen retention Please ensure that any requests for additional investigations on the specimen are made within 3 days from the date of the original request


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