Table 1. DescriptIon and Effectiveness of the Various Modalities of Testing the Adrenocortical Response after a124-Corticotropin Administration

1450 CLINICAL CHEMISTRY, Vol. 29, No. 7, 1983 (GHb), electrophoresis on agar gel has an advantage over the simple chromatographic methods in that it is unaffected by variations in temperature or minor variations in pH or ionic strength of the buffer. With commercially prepared plates, results correlate well with those by liquid chromatography. Commercially prepared plates are expensive so we have prepared agar plates according to the method of Menard et al. (1), using Bacto Agar (Difco Labs., Detroit, MI 48232; cat. no. 0140-01, batch no. 675025). With these plates, the results were reproducible (the CV was 5.4% for Glib = 7.7%, 5.6% for GHb = 19.5%) and correlated well (r = 0.93) with those determined by HPLC (2). However, when we subsequently used different lots of Bacto Agar, the GHb values were substantiallyhigher than those obtained by HPLC: the mean Glib values from four lots of Bacto Agar were 9.5%, compared with an HPLC value of 7.1%, and 20.9% (HPLC, 17.2%). Measurement of the relative electrophoretic mobilities of albumin and Blue Dextran (Pharmacia) on plates prepared from the various agar batches indicated no great difference among them in electroendosmotic flow. When we altered the charge density of the agar medium by adding lactate, pyruvate, dextran sulfate, purified agar, or agarose, the Glib values were lower, but inconsistently so. Thus, we suggest that anyone preparing their own agar plates for the electrophoretic determination of GHb should pay particular attentionto any changes of the type and batch numbers of the agar used, once their method has been standardized.