November 2012
Feature Story

Anne Ford

The truism “With great power comes great responsibility” has been attributed to everyone from Voltaire to Spider-Man (Spider-Man’s Uncle Ben, actually, for those of you with a stash of Marvel Comics). If whoever said it were inside a modern-day laboratory, he’d probably add: “With more sophisticated testing comes more requirements.”

That’s what coagulation laboratory personnel are learning with the recent release of a special edition of Laboratory Accreditation Program coagulation checklist requirements. The new requirements charge coagulation laboratories with performing calibration verification and analytical measurable range validation for particular test methods.

That’s because, says Charles Eby, MD, while “it would not have been appropriate to apply these principles to the older coagulation tests that were not linear and did not measure a concentration of an analyte, coagulation testing has evolved. Methods that were established in chemistry are now used in coagulation. The CAP has clarified the requirements so these principles may be applied to selected coag tests.” Dr. Eby is chair of the CAP Coagulation Resource Committee and professor in the Department of Pathology and Immunology, Washington University School of Medicine, St. Louis.

The new requirements apply only to hemostasis test methods that are calibrated and that directly measure the concentration or activity of an analyte by employing EIA, immunoturbidity, and chromogenic methods. “For many laboratories that have a limited coagulation test menu, this will have no impact,” Dr. Eby says.

Among the commonly performed tests to which the new requirements do apply: calibrated EIA or immunoturbidity methods for coagulation factors, protein C antigen, free and total protein S antigens, von Willebrand factor antigen, von Willebrand collagen binding activity, and quantitative D-dimer, as well as calibrated chromogenic assays for antithrombin activity, protein C activity, and heparin or low-molecular-weight heparin. This is not an exhaustive list, and clot-based methods and all platelet function assays are exempt.

If this all seems like a lot to think about, consider the advice of another truism: “When all else fails, read the instructions.” Or, as Gerald Hoeltge, MD, chair of the CAP Checklists Committee and a pathologist at the Cleveland Clinic, puts it in this instance: “The first place people should look is in the explanatory language.”

He’s referring to the three-and-a-half pages of definitions and discussion that precede the actual requirements. “It looks intimidating,” but it’s not, he says. Rather, those pages consist of “a lot of helpful extra language to try to get people to understand the context” of the new requirements. Included are discussions of suitable calibration verification materials, the analytical measurement range validation process, and related subjects.

The AMR section is likely to be especially helpful to coagulation personnel who have limited chemistry experience. “This is the concept that could be more novel and unfamiliar to some specialists in coagulation,” Dr. Eby says. “The analytical measurable range validation is as important as the calibration verification because it is confirming that previously tested patient samples—or materials that are similar enough to patient samples in terms of matrix properties—produce the expected result. There are a number of ways to do the AMR testing that are outlined in the introduction to the new requirements.”

For example, in a paragraph titled “Linearity and the AMR,” the introduction notes: “For commercially available ‘linearity’ sample sets, it is expected that a plot of the measured values vs. the target values has a linear relationship because there is a known quantitative relationship between the concentrations or activities in the sample set. Alternatively, one can make admixtures of appropriate materials of high and low analyte concentrations and demonstrate that there is the expected linear relationship between measured values of these admixtures and the expected values based on the proportion of low and high concentration samples in each admixture. With either approach, the values should be suitably spaced across the AMR, preferably equidistant from each other.”

The new regulations may spark confusion for some because of a difference between the way in which coagulation results and chemistry results are generally reported. Some coagulation results are reported as a percentage, whereas chemistry results, of course, tend to be reported in terms such as “20 milliliters per deciliter.”

Did the accreditation program take that fact into account when creating the new requirements? “Yes, and that was then brought to the CAP Instrumentation Resource Committee and the Coagulation Resource Committee for our input,” Dr. Eby says. “We agreed that many coagulation tests do not have purified standards, as are available in chemistry. But there are standards, nevertheless, that are designated by international units, or IU. And it is very common in coagulation testing to equate 100 percent with 1 IU. And many assays that we do report in percentages can be traced back to an international unit standard.”

He and Anthony Killeen, MD, PhD, chair of the Instrumentation Resource Committee, felt it was appropriate to apply the principles of AMR and calibration verification to these methods if there was a calibrator in IU available to manufacturers when they create their calibrators, he says. “So it is different than chemistry. You cannot purify many of the coagulation tests the way you can purify glucose or sodium. But we do have an alternative way to standardize calibrators.”

Speaking of manufacturers, don’t expect them to provide guidance immediately regarding AMR calibration validation on coagulation tests. “Unfortunately, the manufacturers and vendors of these tests are also new to these requirements,” says Dr. Eby. “And so package inserts are not consistent in providing guidance or information on this. We’re looking forward to that improving over time, so manufacturers can provide assistance that’s in compliance with these requirements.”

In the meantime, laboratories seeking advice or assistance regarding the new requirements are asked to e-mail accred@cap.org. Alternatively, Dr. Eby and Dr. Hoeltge encourage coagulation specialists to confer with their chemistry colleagues about the new regulations. Says Dr. Eby: “I really think this is a wonderful opportunity for chemists and coagulation experts to do a lot of cross-talking and internal consulting.”

Related Links

• Calibration and AMR validation example (PDF, 7 MB)