nephelometry

Nephelometry is a quantitative analytical technique that measures light scattered by particles in a liquid. A light source illuminates a sample in a cuvette, and a detector positioned at a fixed angle to the incident beam records the intensity of scattered light. The measured signal increases with particle concentration, enabling quantification of the solute. Nephelometry is distinguished from turbidimetry, which assesses the decrease in transmitted light; nephelometry focuses on scattered light to reduce interference from unscattered light.

Immunonephelometry uses antigen–antibody reactions to form complexes that scatter light. Under controlled conditions, the amount of scattering is proportional to analyte concentration, allowing sensitive measurement of proteins in serum. Modern nephelometers employ photomultiplier detectors, regulated light sources, and automated sample handling. Measurement angles typically range from about 20° to 40°, though some setups use other angles or multiple angles; calibration with known standards establishes a quantitative curve. Results are reported in nephelometric units (NU) or converted to conventional units using calibration.

Common clinical applications include quantification of immunoglobulins (IgG, IgA, IgM), C-reactive protein, and complement components such as C3 and C4. Nephelometry is valued for its speed, precision, and compatibility with high-throughput automated analyzers. It is also applied in research and some industrial contexts to measure specific proteins or analyte–antibody complexes.

Limitations include interference from high lipid content, lipemia, sample turbidity, or heterophilic antibodies; multiple scattering at high concentrations can compromise linearity; and standardization across different instruments can be challenging. Proper dilution, controls, and calibration are necessary to ensure accuracy.