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We describe a simple radioimmunoassay (RIA) for estimating concentrations of somatomedin-C (Sm-C) in dried blood on filter paper. A single 3.2-mm blood spot specimen on filter paper is eluted overnight into buffer containing antibody and 125I-labeled Sm-C. The following day, bound and free hormones are separated by addition of goat anti-rabbit gamma globulin in 60 g/L polyethylene glycol solution. The correlation between values obtained for such blood-spot discs and the corresponding wet plasma is highly significant (r = 0.90, p less than 0.001). The relative concentrations (arbitrary units) of Sm-C as determined for specimens on filter paper from mothers and infants, and for cord bloods, are similar to those reported by others using acidified serum.

I describe an improved procedure for estimating thyroxine in dried blood on 0.32-cm filter paper discs, by radioimmunoassay. A weak anion-exchange resin is used to separate free and antibody-bound radiothyroxine and, by measuring the resin-bound 125I-labeled thyroxine rather than the supernatant radioactivity, a tedious and cumbersome step is eliminated. The unique properties of the resin permit considerable latitude in the experimental conditions, in contrast with charcoal, without compromising sensitivity or precision. There is excellent correlation between thyroxine values obtained from discs and those of the corresponding plasmas. Application of this procedure for large-scale screening of newborns has proved to be highly successful in identifying thyroid insufficiency in several babies before clinical signs were apparent.

We report the use of Staphylococcus aureus rich in protein A as an immunoadsorbent in the radioimmunoassay of thyrotropin and thyroxine in blood collected from newborn infants and dried on filter paper. The procedures for thyrotropin and thyroxine, which differ mainly with respect to concentration and volume of the Staphylococcus aureus suspension, are reliable, rapid, and technically simple. The ease of this method, coupled with its dependability, offers certain advantages over some of the commonly used techniques of separation, and therefore it provides a unique approach to measurement of these analytes in laboratory screening programs for neonatal hypothyroidism.

I describe an improved procedure for estimating thyroxine in dried blood on 0.32-cm filter paper discs, by radioimmunoassay. A weak anion-exchange resin is used to separate free and antibody-bound radiothyroxine and, by measuring the resin-bound 125I-labeled thyroxine rather than the supernatant radioactivity, a tedious and cumbersome step is eliminated. The unique properties of the resin permit considerable latitude in the experimental conditions, in contrast with charcoal, without compromising sensitivity or precision. There is excellent correlation between thyroxine values obtained from discs and those of the corresponding plasmas. Application of this procedure for large-scale screening of newborns has proved to be highly successful in identifying thyroid insufficiency in several babies before clinical signs were apparent.

We describe a simple radioimmunoassay (RIA) for estimating concentrations of somatomedin-C (Sm-C) in dried blood on filter paper. A single 3.2-mm blood spot specimen on filter paper is eluted overnight into buffer containing antibody and 125I-labeled Sm-C. The following day, bound and free hormones are separated by addition of goat anti-rabbit gamma globulin in 60 g/L polyethylene glycol solution. The correlation between values obtained for such blood-spot discs and the corresponding wet plasma is highly significant (r = 0.90, p less than 0.001). The relative concentrations (arbitrary units) of Sm-C as determined for specimens on filter paper from mothers and infants, and for cord bloods, are similar to those reported by others using acidified serum.