Immunochemical Determination of Human Immunoglobulins:Use of Kinetic Turbidimetryand a 36-place CentrifugalAnalyzer

We describe the measurement of human immunoglobulins lgG, IgA, and lgM in diluted sera, with diluted commercial monospecific antisera, with use of a 36-place centrifugal analyzer (RotoChem Ila; American Instrument Co., Silver Spring, MD 20920). The assay involves a two-point kinetic turbidimetric technique. The changes in absorbance at 340 nm between 10 and 255 s are taken for standard curve construction with use of a computer-generated cubic least-squares fit. Patients ’ samples are quickly calculated from the stored curve. Multiple time-interval readings are taken to observe the reaction kinetics. The lowest de-tectable concentrations are: lgG, 5 mg/L; lgA, 20 mg/L; and 1gM,20 mg/L. Correlation with radial immunodiffusion was excellent. Precision, accuracy, linearity, and sensitivity were very acceptable. Antigen or antibody excess can b