Measuring of Alpha-1 Antitrypsin Concentration by Nephelometry or Turbidimetry

Most clinical laboratories quantify alpha-1 antitrypsin using either nephelometry or turbidimetry techniques because they are commercially available, amenable to automation, and precise. Both methods are based on light scatter. The foundation of both techniques is based on incubation of the specimen with anti-AAT polyclonal antibody solution, a polymer matrix between endogenous AAT and the reagent antibodies forms, leading to production of light-scattering large particles. Although these two terms are sometimes used synonymously, technically speaking they are not.Nephelometry measures the amount of turbidity or cloudiness of a solution by directly quantifying the intensity of the light scattered by insoluble particles in the sample. Therefore, this technique measures the light that passes through the sample, with the detector being placed at an angle from the sample. Turbidimetry is the process of measuring the loss of intensity of the light transmitted linearly through a sample caused by the scattering effect of insoluble particles. The decrease in light transmission is measured compared to a reference, and the absorbed light is quantified.Beyond specific technical differences between both techniques, there are two major differences between the two procedures that may influence the results. First, the concentration of the sample and the resulting intensity of scattered light relative to the intensity of the light source is one major factor. Second, the size of the scattering particles is also a key differentiating factor. This chapter describes the technical requirements, the different protocols, and the clinical applicability of these two techniques in the diagnosis of alpha-1 antitrypsin deficiency.