Micromethod for the Rapid Determination of Serum Protein-Bound Iodine and Total Serum Iodine

A modification is presented of the chloric acid method for the rapid determination of serum protein-bound iodine and total serum iodine requiring less than 0.5 ml. serum for duplicate determinations. The time required for the entire procedure is less than two hours. By adjusting the amounts of reagents used and by varying the time of digestion, the need for constant and continuous supervision is eliminated. ‘IE1HE DETERMINATION of serum protein-bound io(limle (PBI) by diges-tion with chloric acid as described l)y Zak, O’Neal and others (1-3) with sonic variatioims has met with success hi our laboratory. These variations consist of using 40-mnl. heavy-wall round-bottom tubes for precipitation, washing, digestion, and extractiomi without transfer, a thermostatically controlled electrical block tube heater, amid au adjust-ment of the time interval in time filIal colorimetric procedure. With the almost universal acceptance of the PBI determination as a measure of thyroid function (4-8), especially in the area of pedi-atrics where the Basal Metabolic Bate determination is difficult an(1 unreliable, the need for a trustworthy procedure using microspeci-mens (finger-tip blood) became evident. The recent work of Bird and Jackson (9) seemed to offer a procedure which met this requirement. We found that this method gave a very flat calibration curve, with a resultant loss of sensitivity. Further, the use of room temperature for the catalytic reduction of Ce+4 to Ce+n is miot omily time consuming but requires checking to ascertain the optinmum time for carrying out the colorimetric readings. This led us to attempt to modify our routine macroprocedure using smaller serummmspecimemis: in this method, with 1.0-mi. serum samples, the dligestate is diluted to 10.0 ml. with water and then a 2.0-mI. aliquot of this (equivalent to 0.2 ml. of original sam