Abstract: Calcium in a sample is brought into contact with a transglutaminase capable of being activated with calcium as an activating factor and the transglutaminase activity, which varies depending upon the calcium amount in the sample, is measured to thereby determine the calcium amount in the sample. By the method of the invention, accurate determination of calcium in various samples such as body fluids is possible without removal of proteins from them.

Abstract: The present invention measures serum iron by liberating iron from transferrin under acid conditions, and contacting a test sample with a reaction system which utilizes at least aconitase, a reducing reagent, citric acid, isocitrate dehydrogenase and (thio)NAD(P). According to the present invention, an accurate and efficient measurement of iron in the serum is possible, even for minute levels of iron. In addition, the present invention assays unsaturated iron binding capacity by adding excess iron to a test sample to bind iron to transferrin, binding the remaining unbound iron to aconitase, and measuring the activated aconitase. According to the present invention, a quick and easy assay of unsaturated iron binding capacity of body fluids, etc. is possible without the need for expert skill.