though this would bring them under the purview of HCFA inspectors, it might not ensure quality. It is doubtful that external proficiency tests could be provided economically or efficiently for tests performed only occasionally by many laboratories or that occasional performance of a test can ensure high quality.

To ensure high quality in tests for rare disorders that are seldom performed, the genetics community, under CORN and the American College of Medical Genetics, could take the lead in fostering centralization of these tests. Once centralization occurs and the volume of specific tests performed by the central laboratory increases, a stronger argument can be made that external proficiency testing is economical and efficient. With the establishment of central laboratories, HCFA could consider setting a volume-of-test requirement necessary to ensure quality (as FDA has proposed for MSAFP testing). Laboratories not meeting that requirement would not pass inspection for that particular test. If challenged in court, however, such an arrangement might be considered a restraint of trade. Commercial laboratories, which are often subsidiaries of biotechnology companies, are expanding their range of services and contracting with hospitals, including some academic centers, to take over genetic testing functions.

Interpretation of Laboratory Test Results

For the reasons given earlier in this chapter, the misinterpretation of test results is more likely in genetic tests than in many other areas of clinical testing, and misinterpretation may have more serious consequences particularly in fetal diagnosis. The need for adequate interpretation is even greater when the health care providers ordering tests (1) are not expert in interpreting probabilistic clinical data (Holtzman, 1991); (2) are not expert in genetics; and (3) may not be aware of the implications of both positive and negative test results in genetics. As discussed further in Chapter 6, an increasing proportion of genetic tests will be ordered by primary care physicians, many of whom have limited knowledge of genetics (Hoffman, 1991; Holtzman et al., 1991; Hofman et al., 1993). Special concerns about interpretation also arise when tests may be provided by employers as part of fitness programs or by other organizations not skilled in genetics.

Interpretation can be very complex and can depend on the results of other family members. One way of ensuring that physicians who order tests understand the implications and limitations of results is to require that the laboratory performing the test provide adequate interpretation of the result in its report (Hommes, 1992), although all genetic testing laboratories may not be prepared to provide this service. With few exceptions the interpretation of a positive genetic test result should include the chance of future disease or the chance of having an affected child. In the latter case, the interpretation should note whether the chance is dependent on the carrier status of the mate of the person tested. If misattributed paternity might alter the interpretation, this should also be disclosed. The interpretation of test results should also indicate any confirmatory tests that are avail-

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