Related Experiment Videos
Faulty washers and soiled micropipettors may generate false positive serological results
J V Parry1, P P Mortimer, P Friderich
1Hepatitis and Retrovirus Laboratory, Central Public Health Laboratory, London, UK.
Background:
Serological markers such as HBsAg and anti-HIV may be present in serum at very high concentrations and this may give rise to erroneous diagnoses due to cross-contamination.
Objectives:
To investigate poor equipment maintenance and use, including contamination with human serum, as a potential source of erroneous assay results.
Study Design:
The potential of microtitre plate washers and micropipettors to transfer material between microplate wells and between specimens was examined. For the study of micropipettors we recruited 19 UK diagnostic laboratories.
Results:
Four out of seven plate washers in use, until adjusted, had the potential to cause false positive HBsAg reactions. The centering of the probes that delivered the wash fluid, delivery pressure, wash volume and the use of a pre-programmed card to direct the washing procedure were important variables. We investigated soiling of tip cones of micropipettors. In every laboratory human IgG could be detected in at least a third of eluates from micropipettor tip cones; only 31 (14%) of 222 showed no evidence of contamination with human serum. Only one laboratory submitted eluates devoid of specific antibodies. Anti-HAV was the marker most commonly found (n = 68), followed by HBsAg (n = 27) and anti-HIV (n = 20). Seven micropipettor eluates from two laboratories were radioactively contaminated.
Conclusions:
Recommended precautions are regular checking, cleaning and servicing of equipment, care in interpreting weak reactions, reference back to serum left on the clot of the original specimen and testing of a follow up specimen. Poorly maintained immunoassay equipment can readily generate false positive results due to low-level cross-contamination, particularly with the current highly sensitive HBsAg and anti-HIV assays.
Insights
Poorly maintained laboratory equipment can cause false positive diagnostic results due to cross-contamination. Regular maintenance and careful interpretation of results are crucial for accurate serological marker testing, especially for HBsAg and anti-HIV assays.
Area of Science:
- Clinical diagnostics
- Laboratory equipment validation
- Serological assay quality control
Background:
- High concentrations of serological markers like HBsAg and anti-HIV can lead to misdiagnosis.
- Cross-contamination in laboratory assays is a significant concern for diagnostic accuracy.
Purpose of the Study:
- To investigate equipment maintenance and usage, including serum contamination, as sources of erroneous assay results.
- To identify specific equipment and practices contributing to false positive diagnostic outcomes.
Main Methods:
- Examined the potential for cross-contamination in microtitre plate washers and micropipettors.
- Recruited 19 UK diagnostic laboratories to study micropipettor contamination.
- Assessed eluates from micropipettor tip cones for human IgG and specific antibodies.
Main Results:
- Four of seven plate washers had the potential to cause false positive HBsAg reactions without adjustment.
- Human IgG was detected in eluates from over two-thirds of micropipettor tip cones across all laboratories.
- Anti-HAV, HBsAg, and anti-HIV were commonly found in contaminated eluates; radioactive contamination was also detected.
Conclusions:
- Poorly maintained immunoassay equipment can easily produce false positive results via low-level cross-contamination.
- Regular equipment checks, cleaning, servicing, and careful interpretation of weak reactions are recommended precautions.
- Referencing original specimens and using follow-up testing can help mitigate diagnostic errors.