The Leeds Teaching Hospitals NHS Trust

Pathology

Uncertainty in Microbiology Tests

In laboratory testing there are potential "uncertainties" that may affect test results (for example, specimen not collected correctly, presence of antimicrobials, biological variation)

Additionally factors within the laboratory may lead to variation (for example, incubation times, time to processing). The Microbiology laboratory has measures in place to minimize the level of uncertainty and this is reflected by the Quality Assurance processes in place.

Results provided by the laboratory are representative of the sample tested and must be considered against clinical presentation. There are a number of factors that may affect the quality and validity of a result that are outside of the laboratories control:

 

Factors that may affect results:

Mitigating actions:

Delays in transportation of samples. Isolation or quantification of some microorganisms may be affected by prolonged storage of a sample.

Ensure samples are sent as soon as possible via transport (external) or airtube (internal)

If problems with transport occur contact the laboratory.

Notify the laboratory of any urgent samples

Ensure the date of collection is clearly marked so any possible decrease in quality can be noted on the report

Incorrect storage conditions for sample type e.g. TB QuantiFERON and T spot tests must not be refrigerated and samples must be received within 16 hours

User manual provides full information on sample collection and transport information

Special blue bags are provided to allow laboratory staff to easily identify these samples

See website: How to sample TB QuantiFERON

Inappropriate sample type sent for investigations

Examples:

Copan liquid swabs used for Chlamydia or Viral PCR

Plain universals used for urine culture

Formalin pots used for tissue samples for microbiological culture

Blood tubes with preservatives sent for serology tests

Refer to user guide and tests and tubes website

Contact laboratory if unsure of requirements

Print specimen user guides.

Insufficient volume of sample sent

Refer to user guide and tests and tubes website

Contact laboratory if unsure of requirements

 

Out of Date specimen container used

Do not overstock areas

Practice stock rotation

Check expiry dates before use

Contamination of samples

Always use sterile containers

Maintain aseptic technique

Where appropriate refer to sampling guidance on Leeds Healthcare Pathways

Sample Quality

Maintain aseptic technique

Where appropriate refer to sampling guidance on Leeds Healthcare Pathways

Refer to user guide and tests and tubes website

Insufficient Clinical Details - tests may often be designated within the laboratory based on the clinical details provided. Tests may be missed if there is not enough information

Complete requests as fully as possible

 

Presence of antimicrobials

Where possible take samples before therapy is started

State any antimicrobials in use on the request form

Inherent Factors e.g. Age, gender, congenital immunosuppression

Advice on the need to always provide full clinical details

Medical authorisation of results