Composition and method are provided for the pretreatment of serum prior to a thyroxine assay. Prior to carrying out of the assay, particularly an immunoassay or competitive protein-binding assay, the serum sample is combined with cyclodextrin preferably in combination with an hydroxylated aromatic carboxylic acid in a basic medium, in amounts sufficient to minimize interference with obtaining an accurate and reliable determination of polyiodothyronine in the serum. Normally, after the reagents have been added to the serum, a small incubation period is allowed, after which time the additional reagents may be added for carrying out the assay.

Materials and compositions for making triglyceride controls, calibrators and standards are described. The materials are mono- and di- and tri- glycerides of medium length fatty acids mixed into compositions of human serum or other protein solutions to form stable, miscible solutions suitable for use as controls, calibrators and standards in clinical chemistry for measurement and quality control in assays for triglycerides. The materials described have been used as vehicles for oil-soluble, water-insoluble pharmaceuticals and as facial emollient oils for cosmetics, and as such are safe, functional, stable, rancid-resistant and very inexpensive compared with pure materials synthesized or described previously.

The present invention provides a process for the determination of the .beta.-lipoprotein fraction (LDL) in body fluids, especially in serum or plasma, wherein the LDL fraction is selectively precipitated from the sample by the addition of a polyvinyl sulphate with monovalent cations and then determined. The present invention also provides a reagent for the determination of the .beta.-lipoprotein fraction (LDL) in body fluids, especially in serum or plasma, wherein it contains polyvinyl sulphate.

Processes are described for the selective extracorporeal precipitation of low density lipoproteins or beta-lipoproteins from whole serum or plasma, wherein a treating agent comprising heparin or a polyanion, such as dextran sulfate or sodium-phosphorus tungstate, in a buffer is added to the whole serum or plasma and the beta-llipoprotein-complex which thereupon forms with the treating agent is precipitated at the isoelectric point at a pH value in the range of from about 5.05 to about 5.25, and is then separated. Optionally, the precipitate or respecively the filtrate is further analyzed for diagnostic purposes. When heparin is employed, the process may be employed therapeutically. Apparatus is described for the continuous therapeutic practice of such a process, employing heparin, including means for flushing to reduce clogging of the filter employed to separate the precipitated lipoprotein-complex.

A consistent, stable serum having good optical qualities and improved filterability suitable for control and calibration uses is disclosed as well as its method of preparation.