The relative merits of polyethyleneglycol as a separating agent in the radioimmunoassay of thyroid hormones

Polyethylene glycol in conjunction with a second antibody for 24-hour radioimmunoassays of bovine prolactin and growth hormone

Separate 24-h radioimmunoassays were validated for bovine prolactin and growth hormone using polyethylene glycol in conjunction with a second antibody for separating bound from free labeled hormone. Buffer, standards, sera, antisera, and radioiodinated hormone were added to assay tubes and incubated 24 h. The second antibody was added and incubated for 15 min. Then 1 ml of 6% polyethylene glycol (3% final concentration) was added, and tubes immediately were centrifuged. Polyethylene glycol effectively decreased incubation time. There was no significant difference of percent binding, percent nonspecific binding, or sensitivity of these assays as compared to assays requiring a 72-h incubation with the second antibody when polyethylene glycol was not used. Specificities of the assays were demonstrated by parallelism between varying volumes of bovine serum and standard hormones. Sensitivities of the assays were .4 and .8 ng for prolactin and growth hormone. Intra- and interassay coefficients of variations were 8 and 12% for prolactin and 5 and 18% for growth hormone. Recoveries of known amounts of added hormones were 81 and 75% for prolactin and growth hormone.

Interlaboratory comparison of serum thyroxine analyses

Approximately 300 clinical chemistry laboratories participated in a survey of measurements of the thyroxine (T4) concentration in 13 lyophilized serum specimens prepared by spiking a base serum pool with several different levels of T4. Of 35 commercially available kit methods, 4 kits were used by 30 or more laboratories, and 9 by 10 or more laboratories. Values obtained with the Abbott or Nuclear Medical laboratories, kits, which were used by one-third of all laboratories that named a specific kit, averaged 1 to 2 micrograms/dL greater than those obtained with the other methods. Within-run coefficients of variation were 10 to 20% for specimens containing less than 3 micrograms/dL of T4 and 3 to 6% for specimens with more elevated T4 levels.

Anti-acetylcholine receptor antibody: use of polyethylene glycol as an aid to precipitation of antibody-receptor complexes in determination of light chain and subclass

Polyethylene glycol 6000 (PEG) was used as an aid to precipitation of antibody-acetylcholine receptor (AChR) complexes. In the absence of anti-human IgG, 8% PEG can be used to precipitate antibody-AChR complexes. In the presence of low titre specific antiserum, 3% PEG selectively precipitates anti-IgG-IgG-AChR complexes and allows analysis of light chain and subclass contribution to the anti-AChR. The specificity of the various antisera is presented and results in 16 patients described.