Originally published in CAP TODAY
Q: Question AGC.24130 in the automated/general chemistry checklist reads, "Are common interferences evaluated for all analytes measured with each reagent system, or is information available that is consistent with NCCLS Guideline EP7-P (Interference testing in Clinical Chemistry)?" NCCLS states the manufacturer has the comprehensive study and that it is not necessary to repeat. Assuming the laboratory abides by the manufacturer's claims, would you answer yes, no, or n/a, since the manufacturer states the interferences?
A: This question was revised slightly in September 2001 to read: "Are common interferences evaluated for all analytes measured with each reagent system, or is credible information available?" Instead of including the NCCLS document in the question proper, it is mentioned as part of an accompanying note: "NCCLS Guideline EP7-P (Interference Testing In Clinical Chemistry) is a useful reference source. Neither this document nor its methods are mandatory for CAP accreditation."
Six references are provided, including the one from NCCLS:
- Letellier G, Dejarlais F. Analytic interference of drugs in clinical chemistry. 1: Study of twenty drugs on seven different instruments. Clin Biochem. 1985;18:345-351.
- National Committee for Clinical Laboratory Standards. Interference testing in clinical chemistry; proposed guideline EP7-P. Wayne, Pa.: NCCLS, 1986.
- Kroll MH, Elin RJ. Interference with clinical laboratory analyses. Clin Chem. 1994;40:1996-2005.
- Kazmierczak SC, Catrou PG. Analytical interference. More than just a laboratory problem. Am J Clin Pathol. 2000;113:9-11.
- Tang Z, et al. Effects of drugs on glucose measurements with handheld glucose meters and a portable glucose analyzer. Am J Clin Pathol. 2000;113:75-86.
- Tang Z, et al. Effects of pH on glucose measurements with handheld glucose meters and a portable glucose analyzer for point-of-care testing. Arch Pathol Lab Med. 2000;124:577-582.
We do not require each laboratory to conduct an exhaustive study for interferences. If there is manufacturer-supplied information, you must carefully review that material and judge its relevance/acceptability for your setting. For example, if there are no neonates with very high serum unconjugated bilirubin in your patient population, then bilirubin interference may not be relevant to you. Conversely, there may be a focal need for you to do some followup, such as evaluating lipid interference if you support a hyperglycemia clinic and the instrument-reagent manufacturer has not evaluated lipemia as a potential source of interference with your assays. In the current era, laboratories must assess interferences beyond the traditional limited trio (hemolysis, icterus, lipemia) that were the bane of older, wet chemistry assays.
Q: As laboratory manager, I handle a large portion of the laboratory general checklist during inspections. I think that booklet could be reviewed, from a field perspective, to make it easier (especially for the inspector) and less redundant (related to content, which also appears in the section booklets). I also think the content of the laboratory general checklist is too much for one manual and one inspector. I base this last opinion on my experiences as a CAP inspector and our recent CAP inspection.
A: Deciding what elements to include in the laboratory general checklist versus the section-specific checklists is always difficult and intrinsically imperfect, given the great heterogeneity of laboratories' organizations and the style of each inspection team. Indeed, we receive equal numbers of complaints that something is repeated in each of the section-specific checklists ("lumpers") versus complaints that an important item in the laboratory general checklist should be repeated in each of the section-specific checklists ("splitters").
In general, we try to avoid repeating laboratory general items in the section-specific checklists. Controlling the proliferation of the numbers of questions represents one of my major challenges. There is a general tendency to add new requirements without deleting existing ones, although we have done so and will continue to discard the less clinically and scientifically important ones. We recognize that the laboratory general checklist is probably a full day's work for one inspector, who is usually the team leader. However, that checklist can be easily separated and distributed among the inspection team members. Each team is free to divide up the work any way it wishes. A related issue is the need to remind everyone that the laboratory general checklist applies to all sections of the laboratory.