Quality control of acid phosphatase assay improved by direct reconstitution of lyophilized control materials with citric acid.

Current quality control of assays of acid phosphatase (EC 3.1.3.2) with thymolphthalein substrate is inadequate when certain control-suppliers' instructions are followed for reconstituting and stabilizing human lyophilized control material. If such materials are reconstituted with a citric acid solution, then stored frozen, control vial-to-vial variability is minimized, as are losses of activity in freshly reconstituted controls and losses during room-temperature storage of the control material. Effects of pH of the reconstituting solution on the acid phosphatase activity of human lyophilized controls are also discussed.