Introduction

Until the 1960s, quantitative methods of measuring low concentrations of albumin were laborious as they depended on the separation of protein by electrophoresis after concentration of the urine. In 1963, Keen and Chlouverakis described an immunoassay which was specific for albumin, required only small volumes of urine, was accurate and sensitive and was capable of dealing with large numbers of samples. This trail-blazing paper was not only the forerunner of many methodological developments, but also the starting point of much exciting research which has eventually established the significance of small amounts of albumin in the urine. Such increases in albuminuria which are undetectable by conventional dip-stick testing but greater than the normal excretion have been called microalbuminuria.

Laboratory measurement of microalbuminuria

General considerations

As discussed above, the assay must be specific for albumin, and hence have an immunological basis. It must be precise, sensitive and practicable. Currently the techniques commonly used are radioimmunoassay (RIA), single radial immunodiffusion (RID), immunoturbidimetry (IT), laser immunonephelometry (IN), and enzyme-linked immunosorbent assays (ELISA) (Table 2.1). There are many variations of each method and little has been published on comparisons of different techniques.