a fair price for the test. This should serve as an incentive to accelerate data collection. Data collection can also be speeded by enabling investigators to collaborate, pooling their data. For very rare diseases, commercial sponsors of such collaboration are unlikely to be forthcoming. Support for collaborative studies will greatly speed the process of making these tests available to the public, and long-term support may be needed to conduct some of these studies.
An estimated 4 million screening blood specimens from heel-sticks of newborns are tested annually in the United States for at least one genetic disorder. Many of these tests are performed in state laboratories; some state laboratories subcontract work to commercial laboratories (Table 3-1). CDC provides the only proficiency testing program for newborn screening in the United States. For 39 state and territorial and 28 private laboratories participating in proficiency testing for newborn screening, CDC absorbs the cost of the testing program.
Participation in the program is voluntary; 115 organizations participate, including manufacturers and international laboratories, 39 state and territorial laboratories, and 28 private laboratories. Data on the quality of programs participating in CDC's voluntary program show substantial error rates, in excess of 5 percent false negatives (Holtzman et al., 1986; Adam and Hannon, 1992). CDC has consulted HCFA concerning approval of the CDC newborn screening proficiency testing program as a provider of proficiency testing under CLIA88; at present, CLIA88 regulations cover only one of the ten newborn screening tests, hypothyroidism (using thyroxine and thyroid stimulating hormone) (B. Adam, CDC, personal communication, January 1993).
Errors in screening for genetic disorders may also be greater than for other tests because it entails the testing of many people who will not have the condition being screened for. This is true in carrier and prenatal as well as newborn testing. When tests of high sensitivity and specificity are used in populations in which the condition being screened is of low prevalence, the predictive value of the result may be low. If, in addition, laboratory error adds substantially to the number of false negatives and false positives, the safety and benefit of screening come into question. This concern is all the more important because unlike many other medical procedures, it is usually not the patient who initiates the process but the health care provider or the state (in the case of newborn screening). This increases the possibility that the person being tested could misunderstand the objectives of testing and misinterpret the results. Errors in screening may also be greater than in other medical tests because many specimens are handled simultaneously and may be analyzed at a site far removed from where they were obtained. Thus the entire screening process, from informing the patient (or parent) through final disposition (giving the patient or parent the result or placing it on the patient's record), should be subject to quality control.