Abstract: Theophylline can be determined with an analytical element and method which utilize the inhibition, by theophylline, of alkaline phosphatase activity on an appropriate substrate. The assay is carried out at a pH of 9 or less. The element comprises a porous spreading zone, a subbing zone and at least one other zone. The zones are in fluid contact with each other. The isoenzyme of alkaline phosphatase and a suitable substrate for the isoenzyme are located in different zones of the element. The subbing zone contains polyvinylpyrrolidone and a buffer for maintaining a pH of 9 or less.

Abstract: An analytical element can be used for the determination of either creatinine or creatine or both. The element contains creatinine amidohydrolase, creatine amidinohydrolase and sarcosine oxidase, and a leuco dye which is capable of providing a detectable dye in the presence of hydrogen peroxide and a peroxidative substance. The creatine amidinohydrolase is present in a manner such that it is substantially inert to the leuco dye. The creatinine amidohydrolase is present in a rate limiting amount. By measuring the amount of dye formation at particular times during the assay, either or both of the analytes can be determined with the same element.

Abstract: Theophylline can be determined with an analytical element and method which utilize the inhibition, by theophylline, of alkaline phosphatase activity on an appropriate substrate. The assay is carried out at a pH of 9 or less. The element comprises an absorbent carrier material, a suitable buffer and first and second zones in fluid contact. The isoenzyme of alkaline phosphatase and a suitable substrate for the isoenzyme are located in different zones of the element. The isoenzyme is present in one of the zones in an amount of at least about 100 I.U./m.sup.2. This level of isoenzyme reduces or eliminates bias caused by endogenous alkaline phosphatase and hemoglobin during an assay.

Abstract: Theophylline can be determined with an analytical element and method which utilize the inhibition, by theophylline, of alkaline phosphatase activity on an appropriate substrate. The assay is carried out at a pH of 9 or less. The element comprises a porous spreading zone and at least one other zone in fluid contact with the spreading zone. The isoenzyme of alkaline phosphatase and a suitable substrate for the isoenzyme are located in different zones of the element. The element also contains a buffer for maintaining the pH at 9 or less, substantially all of which is located in the spreading zone.

Abstract: Theophylline can be determined with an analytical element, composition, kit and method which utilize the inhibition, by theophylline, of alkaline phosphatase activity on an appropriate substrate. The assay is carried out at a pH of 9 or less. The element comprises an absorbent carrier material, a suitable buffer for maintaining the pH at 9 or less, and, in fluid contact, a first zone containing an isoenzyme of alkaline phosphatase which is capable of activity at pH 9 or less, and a second zone containing a substrate for the isoenzyme. Use of this invention avoids the effect of endogenous alkaline phosphatase found in human biological fluids which has no activity at pH 9 or less.

Abstract: A multilayer analytical element for the determination of creatine kinase comprises a support having thereon, in order and in fluid contact, a registration layer and an isotropically porous spreading layer. The registration layer contains a binder material at a coverage of at least about 8 g/m.sup.2, which coverage improves the stability and keeping properties of the element in high humidity environments. This element is useful in an analytical method for determining total creatine kinase or any one of its isoenzymes, e.g. creatine kinase-MB.

Abstract: Disclosed herein is a dry analytical element and a method of using same for quantitatively detecting alkaline phosphatase in an aqueous liquid. The element comprises, in fluid contact, first and second reagent zones which can be self-supporting or carried on a support. The first reagent zone contains a substrate for alkaline phosphatase, e.g. p-nitrophenyl phosphate, and the second reagent zone contains a buffer which is an alkali metal or ammonium salt and has a pKa in the range of 9-11.5, e.g. an alkali metal salt of carbonic acid.