Mid-stream urine (MSU)

A clinical diagnosis of urinary tract infection (UTI) can be confirmed by culture.
Microscopy is performed on a fully automated cytometry analyser. Manual microscopy is only performed as an alternative if the specimen is not suitable for the automated method. The cytometry or microscopy is used as a screening test to screen out all negative urine samples in the majority of samples.
Urine samples with positive cytometry or microscopy will be cultured for isolation, identification and susceptibility of likely pathogens. Samples from specific groups will have automatic culture irrespective of cytometry or microscopy result (such as children, transplant, renal, oncology, haematology and obstetric patients).
Not all susceptibility test results are routinely released and additional advice can be obtained from the consultant microbiologist if required.
Clinical details: 
Urinary tract infection, dysuria, pain on micturition. The following clinical details will trigger a compulsory culture: recurrent UTI/cystitis, treated UTI, non-resolving UTI, pyelonephritis, reflux. The following wards and patients will trigger a compulsory culture: renal, oncology, obstetrics, paediatrics (<14 years old), urology, haematology.
Any culture result must be interpreted in context of the clinical picture.
Synonyms or keywords: 
MSU , mid-stream urine
cytometry results: RBCs <10/µl reported as non-significant numbers detected, 10-99/µl reported as small numbers (10-100/µl) detected, 100-199/µl reported as moderate numbers (101-200/µl) detected, >199/µl reported as large numbers (>200/µl) detected. WBCs <10/µl reported as non-significant numbers detected, 10-49/µl reported as small numbers (10-50/µl) detected, 50-199/µl reported as moderate numbers (51-200/µl) detected, >199/µl reported as large numbers (>200/µl) detected. Bacterial <400/µl reported as non-significant numbers detected, ≥400/µl reported as significant numbers detected Epithelial cells ≥15/µl reported as Epithial cells detected Samples with a cytometry count of <20/µl WBC and/or <150/µl bacteria are not cultured Manual microscopy - performed if sample unsuitable for processing via automated cytometry or in event of instrument failure, all samples are cultured if manual microscopy is performed.
Sample type and Volume required: 
10 ml of urine in a green topped monovette urine tube containing boric acid is the preferred sample. Samples received in the lab by 19:00pm will be set up for culture the same day.
Where possible please send separate samples for individual tests as samples may be processed in different departments such as cytology or virology.
Please indicate where a high risk pathogen may be implicated (such as Salmonella typhi)

Turnaround time: 
Microscopy/cytometry 4hrs, negative culture 1 day, postive cultures 2-3 days.
Patient instructions: 

Start to urinate and collect a sample of urine "mid-stream" in a sterile screw-top container.

Storage and transport: 
Place the labelled sample in a sealed sample bag and send to Central Specimen Reception (CSR). Samples should be refrigerated if transport to the laboratory is delayed.
Infection Sciences Department at St Thomas' Hospital
020 7188 8008
St Thomas' Hospital
North Wing - 5th Floor
Westminster Bridge Road
London SE1 7EH
Core opening hours: Monday-Friday 0900-1730

For clinical advice or interpretation of results, please contact the laboratory in the first instance.

Print as a PDF

Last updated: 29/04/2019