Comparisonof Per - cent of ExpectedValue and Percent Recoveryfor Serum Folate Radioassay

The LKB 8600 Reaction Rate Analyzer sold in the United States, is equipped with a “delay switch,” whereas the same instrument sold in Canada measures time rate reactions immediately after the addition of the initiating reagent, without provision for delay. Therefore, “lag-phases” of any enzyme reaction are recorded with the Canadian version. One of the basics of zero-order kinetic assays is the measurement of the linear phase of reaction. This rule cannot be observed if an instrument such as the LKB 8600 is used without a modification to permit delayed measurements. Both CPK and LDH determinations may give erroneously high results in such a system, especially if a computer printout is used. Boebringer Mannheim has investigated the possibilities of shortening the “lag-phase” for CPK determinations. It was found that the use of chromatographically pure creatine phosphate in the assay reduces the phase to less than 1 minute, but costs increase four to five times. To rectify the problem for routine laboratory, the following steps have been taken: 1. Since July 1971, Canadian customers who use the CPK kit (BMC Cat. No. 15926) with the LKB 8600 are given ATP-free creatine phosphate free of charge. 2. During 1972, a new CPK test kit (BMC Cat. No. 15721) was introduced, especially designed for the use with the LKB 8600 and other automated instruments. This kit contains ATP-free creatine phosphate of the highest purity. We must emphasize that our Test Combination (BMC Cat. No. 15926) for the determination of CPK activity does give correct results when used according to the printed insert. The methodology is based on proposals made by Rosalki. Any modification to the operating instructions should first be discussed with our Technical Services Department. It is regretful that often attempts to economize the work-load results in over-asking for the possibilities df the given instrument-reagent combinations.