Clinical applications of protein determinations in biological fluids other than blood

Over the past decade, significant improvements in immunochemical and electrophoretic techniques have enabled collection of heretofore unavailable data on proteins in biological fluids, greatly increasing our understanding of protein physiology in the various body compartments and providing the foundation for clinical use of protein analysis in body fluids. The most striking advance has been in the diagnosis of demyelinating disease through the use of serum/cerebrospinal fluid protein ratios and the morphological evaluation of immunoglobulin banding patterns. These laboratory tests are now considered obligatory for any patient in whom demyelinating disease is suspected as the cause of neurological dysfunction. Cerebrospinal fluid protein data can also be helpful in quantitating the permeability of the blood/cerebrospinal fluid barrier in many inflammatory or infectious central nervous system disorders. Assays of individual proteins in urine can help distinguish between different types of proteinuria, and can give quantitative data on the selectivity of the glomerulus and the reabsorbing capacity of the tubules. The protein content of saliva, synovial fluid, and milk has also been well characterized, and is clinically applicable to a wide range of disorders.