Adding a new molecular test to your lab? Make sure you understand the regulations that apply and the required performance characteristics. The following is the first in a series of articles on this topic that will include best practices.
Before we dive into the how of verification for molecular diagnostic assays, let’s take a look at the what.
- Clinical laboratories performing an FDA-cleared or FDA-approved test must verify that the manufacturer’s performance characteristics can be met or exceeded
- Laboratories performing laboratory-developed tests (LDTs) and modified FDA-cleared or approved tests, must verify the same characteristics, plus determine analytical sensitivity and analytical specificity
FDA-cleared or FDA-approved test
You must verify and document accuracy, precision, reportable range and reference interval.
Accuracy is verified when test results fall within the manufacturer’s stated acceptable limits. Labs may use commercially available calibrators/calibration, quality control materials, proficiency testing materials, previously tested patient specimens, a reference method or even split samples with another method shown to be accurate.
Precision is achieved when labs can repeat a test under different conditions and have comparable results multiple times in the same run and in different runs on different days.
Reportable range is the span of values, highest to lowest, the lab can accurately verify for a specific assay. For Clinical Laboratory Improvement Amendments of 1988 (CLIA ‘88), the reportable range must not exceed the range of the available calibrators.
Reference interval is the range of values between which the results of a specified percentage of healthy individuals would fall. A suitable number of specimens need to be evaluated to verify the manufacturer’s normal values or the published reference intervals, whichever is best suited to the lab’s patient population.
Laboratory Developed Tests and Modified FDA-Cleared or Approved Tests
In addition to the above, labs need to verify analytical sensitivity and analytical specificity.
Analytical sensitivity is the lowest concentration of analyte or the lowest amount of material the assay consistently detects.
Analytical specificity is the ability of the assay to detect only the target or distinguish it from other sequences in the specimen.
Verification Needs Ongoing Quality Control
When looking into what performance measures need to be verified, it’s a good time to consider quality control and how that can help make your verification process more efficient and successful.In their paper on molecular diagnostic assay validation, members of the 2013 and 2014 Clinical Practice Committees of the Association for Molecular Pathology offer a list of quality control measures to consider:
- Controls appropriate for each assay (positive and negative controls and a blank, lacking nucleic acid template); quantitative assays should include negative, low-positive, high-positive controls and a blank
- Controls in a biological matrix that simulate clinical samples
- Controls processed in the same manner as patient samples
- Standards used in each run that involves size separation
- Proper calibration of the instruments maintained
- Routine preventive maintenance of all instruments
- Test new lots of reagents side-by-side with the old reagent, prior to implementation
- Participate in national testing programs for all tests performed or participate in an alternative assessment at least twice per year (per CLSI)
- Assess continued technologist competency
- Keep results of validation studies as long as the protocol is in use, and for at least two years after the protocol is retired
Our next article will look at the three steps of molecular diagnostics assay verification. Upcoming posts will focus on best practices for each of the required performance characteristics.
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