How does the pipetting technique that technologists use affect assay development?


In the laboratory services field, it’s not uncommon to have a dynamic range of technologists performing the same functions.  Some technologists are seasoned and have acquired pipetting techniques in various activities throughout their careers; while others may not have ever had to perform a large amount of pipetting in their positions or are simply “out of practice”.  Others may be new to the field and have little or no real experience with pipetting, or conversely could have performed quite a bit of pipetting through various training programs.  The bottom line is that there is a lot of variation due to experience and background.

Q:  How does the pipetting technique that technologists use affect assay development, ongoing assay performance, and ultimately patient safety

Pipette skill variation in specific areas of the clinical laboratory isn’t always acceptable.  If manual pipetting is performed in an area where accuracy and precision are not critical, then variability due to pipetting technique variation can be tolerable.  However, if accuracy and precision are crucial in areas where manual pipetting is performed (e.g. quantitative PCR), then consistent, proper pipetting techniques amongst technologists is essential.

Potential Sources of Variation

This applies not only to clinical technologists, but to the scientists who are developing assays for clinical purposes as well.  If the scientist is using a completely different technique to determine the target values for controls and standards, there is a possibility of seeing a vast variation when the assay is introduced to the clinical laboratory.  For example, if assay development scientists use reverse mode pipetting to produce target values, which is known to lead to increased inaccuracy, and the clinical technologists are using forward mode pipetting, then it’s unlikely there will be concordance.  This can cause increased test failures and high sample rejection rates.  Harm may be caused to the patient if delayed or inaccurate results are being provided and used to determine treatment plans.

Method and Procedure

Prior to performing clinical testing, it is a best practice to collect at least 20 data points from various technologists, from different shifts, and over 10 days for each control. This data is used to develop ranges of acceptability for the assay.  The value of measuring the variation using this method is that the ranges will not be set so tight that it would be impossible to meet the criteria.  However, if the acceptable range of variation is set so wide that there are never any rejections, then the chances of providing inaccurate data increase.

Again, the area of testing must be taken into consideration.  For quantitative PCR, very small volumes are used for determining the amount of DNA present.  When pipetting a nearly invisible volume (for example, 5µL), the dispensed volume can cause enough variation that would mean the difference between a false negative and a false positive result. For example, when measuring a viral load, if an inaccurate result is obtained, the patient could receive unnecessary antiviral therapy, which can cause adverse effects and is very costly.

Monitoring ongoing performance is also important.  Setting limits of acceptability is useful in identifying drifts in assay performance.  Investigations may determine that either the assay is failing, or there could be a technique issue with an individual.

Q:  And how much variability can be tolerated?

Training for consistent pipetting technique eliminates the concern of performance variation, reduces rejection rates, and most importantly ensures patient safety.  The means for assessing competent technologists should depend on the expectations of the area in which they will be working.  Evaluation of competence must be measured in order to provide indisputable evidence.  The tolerated variability will depend on the method and complexity of the testing, which should be in balance with the competency level of the technologist.

shilo-caufieldAbout the Expert

Shilo Caulfield, ASQ CQIA

Quality Control Technologist III, Viracor – IBT Laboratories, Inc.



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