According to blood donor screening data, about two-thirds of all initially positive ELISA results are negative on repeat.1
It is assumed that the blood sample for the HIV test is drawn with the standard prenatal panel after informed consent has been obtained. The average cost of $5 per person screened includes the estimated cost of the laboratory test and the cost of providing information that is sufficient for informed consent concerning the purpose, benefits, and risks of the HIV test.
The column "HIV Positive or Indeterminate on ELISA Test" shows the average cost for individuals screened who require Western Blot testing. This includes those individuals who test positive on the first and two repeat ELISA tests. It also includes those who test positive on the first and one of the two repeat ELISA tests; some of these will yield a positive Western Blot result. Some will have a negative or indeterminate Western Blot and require further testing with additional blood specimens. The blood donor screening studies cited earlier have shown that about one-third of those testing positive on the first ELISA were persistently positive on the repeat ELISA, and 10 percent were also positive on the Western Blot. Of those repeatedly but weakly positive on the ELISA, only about 1 percent were positive on Western Blot testing.
To estimate the average laboratory cost a telephone survey was conducted of manufacturers of the reagents and of several commercial and public laboratories in the San Francisco Bay area. Average cost estimates are based on information provided by large public laboratories where economies of scale occur both in terms of manufacturer discounts and in processing the specimens with adequate quality control.
In selective screening, a risk assessment cost will be incurred for all women who present for prenatal care. It is assumed that risk assessment consists of a written instrument that will be part of an intake questionnaire. For most individuals this will be sufficient, although some women with risk factors may need further explanation in the course of the intake visit; the estimate is for average cost.
R. S. Eisenstaedt and T. F.. Getzen, "Screening Blood Donors for Human Immunodeficiency Virus Antibody: Cost-Benefit Analysis," American Journal of Public Health 78(1988):450-454; Irwin Memorial Blood Bank, unpublished data, 1989.