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HIV SEROLOGICAL METHODS; THEIR APPLICATION,INTERPRETATION AND QUALITY CONTROL

Objective

The goals of the Concerted Action were:
to collect information from countries in the European Community (EC) and those taking part in the European Cooperation in the Field of Science and Technology (COST) on:
- how HIV antibody testing is organised, the numbers of tests carried out, techniques used, procedures for confirmation and detecting discrepancies
- the types of quality assessment schemes available and the provision of standard or test sera.
to develop a consensus on the most suitable tests, test strategies and programs of quality assurance so that, with improved international cooperation, the accuracy and comparability of results in the participating countries could be improved.
at a later stage, depending on the outcome of 1 & 2, to facilitate interlaboratory visits for training and arrangements for the exchange of test sera and reagents.
Current laboratory strategies and practice in human immunodeficiency virus (HIV) serological testing and quality assurance were investigated by means of a questionnaire addressed to 167 laboratories in the 12 countries of the European Community together with Finland, Norway, Sweden and Switzerland. Although there were regional differences there was a general pattern of primary and confirmatory tests, the latter often, but not always, being in specialist laboratories. Some form of enzyme linked immunosorbent assay (ELISA) was universal for primary tests often supplemented by others. Confirmation was usually by another type of ELISA or by Western Blot or both. 12 of the 16 countries had their own quality assurance schemes for HIV testing. Of the remainder 2 used schemes from Central Public Health Laboratory (CPHL) London of Centres for Disease Control (CDC) Atlanta, and 2 were about to introduce schemes of their own. All were strengthening the schemes they had. Laboratories varied greatly in size and workload. Validation and confirmation are essential for all but especially for those doing small infrequent numbers of tests. The results suggested that the standard of HIV serology in Western Europe was reasonably uniform so that epidemiological comparisons of different areas had a sound technical base. Nevertheless closer collaboration between countries would be desirable though a formal central organisation seemed likely.
Tests for antibody to HIV became widely available in 1985 and quickly came into large scale use. The three main areas of application are, clinical diagnosis, screening, eg of potential blood donors, and epidemiological surveillance. While accuracy and reproducibility are always essential, the particular requirements for specificity, sensitivity and predictive values are not necessarily the same for the different types of application. This needs to be born in mind even though in practice most current HIV antibody tests, properly carried out, give a degree of accuracy rarely achieved by other serological tests.

Antibody tests are increasing in number and variety. They are becoming procedurally more simple but based on more sophisticated underlying technology. Tests differ in the antigens they use, so that it may not be apparent which specific antibodies are being detected. Unless account is taken of these differences comparisons of different tests may be misleading.

The demand for testing has increased enormously and continues to do so in all fields. It is particularly great in epidemiology which until recently has been dominated by figures on clinical AIDS. These remain essential, but of course are evidence of infection often acquired some years previously. Not only can sero-surveillance detect quite recent infection, it can easily cover very large populations. With the rapid expansion of such surveillance and the desirability of comparing figures from all over Europe, it is essential that test results should be technically as well as epidemiologically comparable.

It is generally accepted that no one should be designated as seropositive on the basis of a single test result and various strategies of confirmatory testing have been evolved. These range from simple repeats, by the same laboratory, of the same test on the same blood sample, to the performance of a complex battery of tests by a reference laboratory on the original and other samples. How far down this path any one specimen should go is a matter for debate and some general guidelines would be valuable.

Who gets tested, when, where and why, are matters of public health policy which differ from country to country. However such decisions affect the types and numbers of tests needed and must be taken into consideration in establishing common testing strategies.

Funding Scheme

CON - Coordination of research actions

Coordinator

Central Public Health Laboratory
Address
61 Colindale Avenue
NW9 5HT London
United Kingdom