INTRODUCTION

This chapter is not designed to cover all the techniques and assays used in clinical immunology. Rather, it is an introduction to various techniques commonly used in diagnosing human disease or, rather, assays to evaluate the competence or incompetence of the immune system. Finally, it will serve as an introduction to the many new techniques emerging in the past several years that have widened our knowledge of the complex relationship of microbe–host interactions in human disease.

Laboratory tests vary widely in clinical immunology. Some are essential for diagnosis while others are useful in subclassifying disorders. Finally, some are of research interest only but may add to our immunological armamentarium in the future. In this regard, it is important to understand that these tests do vary in their sensitivity and specificity.

The sensitivity of a test is defined as the number of diseased individuals that are positive for the test compared with those who are negative. The specificity of a test is the proportion of individuals without a given disease that are negative. Thus, a positive test is really restricted to the disease in question.

The various assays to be discussed later in this chapter can be conveniently divided into two main divisions. Some assays are quantitative in that they produce precise results. Many of these assays are automated and can be related to international standards. Qualitative assays are less specific and will give answers such as normal–abnormal, or positive–negative results. The problem is that interpretation of results may be subjective and require special expertise in carrying out the test.