Clinical Analysis A Perspectiveon Chromatographic and ImmunoassayTechnology More than one billion analyses are performed on blood each year in the US.Two main categories of analysis can now be distinguished based on the yield of medical information ( I ) . The first includes tests that reflect the consequence rather than the cause of disease. This includes such substances as urea, creatinine, total protein, cholesterol, sodium, potassium, calcium, and glucose. Many of these materials occur at relatively high concentration M) and can be measured by relatively simple methods. The second group consists of analyses performed on substances that are thought to be associated with the cause of illness. Blood levels of hormones, vitamins, drugs, antibodies, cells, enzymes, and some proteins can reflect specific tissue damage, inherited metabolic disorders, blocked biosynthetic routes, microbial invasion, drug toxicity, or malfunction of the immune system. These tests often require greater analytical complexity because minute quantities (10-8to
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lo-" M) of a single substance must be specifically determined in the presence of the complex blood matrix (Figure 1). The development of analytical instrumentation for chromatographic methods-liquid chromatography (LC), gas chromatography (GC), and gas chromatographylmass spectrometry (GC/MS)-during the past 20 years was closely paralleled by a development hidden from the view of most analytical chemists. This development, the discovery of immunoassay techniques by Berson and Yalow in 1959, was recognized by the 1977 Nobel Prize in Physiology or Medicine (2). I t proved to be as significant to clinical chemistry as the development of chromatographic instrumentation was to analytical chemistry. In chromatography, improved sensitivity and specificity were achieved with the invention of new detectorsthe electron capture detector for GC, UV and fluorescence detectors for LC, and, for the ultimate in specificity, the
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Analyte Concentration, glmL
Flgure 1. Chromatographic and immunochemical blood tests. The x axis indicates the sensitivity required for specific analytes of clinical interest. The y axis is the molecular weight of the analyte. The analytical challenge is segregated into regions of application for chromatography and immunoassay 682,.
ANALYTICAL CHEMISTRY, VOL. 53, NO. 6, MAY 1981
mass spectrometer combined with GC or LC. Clinical chemists soon applied these developing chromatographic techniques to their needs. A natural fit was found in toxicology and drug monitoring of low molecular weight compounds (
