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:
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Factors that may affect results: |
Mitigating actions: |
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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 |
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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 |
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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 |
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Insufficient volume of sample sent |
Refer to user guide and tests and tubes website Contact laboratory if unsure of requirements
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Out of Date specimen container used |
Do not overstock areas Practice stock rotation Check expiry dates before use |
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Contamination of samples |
Always use sterile containers Maintain aseptic technique Where appropriate refer to sampling guidance on Leeds Healthcare Pathways |
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Sample Quality |
Maintain aseptic technique Where appropriate refer to sampling guidance on Leeds Healthcare Pathways Refer to user guide and tests and tubes website |
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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
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Presence of antimicrobials |
Where possible take samples before therapy is started State any antimicrobials in use on the request form |
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Inherent Factors e.g. Age, gender, congenital immunosuppression |
Advice on the need to always provide full clinical details Medical authorisation of results |
