For comparison, the alkaline phosphatase activities were evaluated on a plate reader using the standard colorimetric assay . In short, 100 μL of sample was prepared containing the reference standard or serum at five-fold dilution in 100 mM Tris•HCl pH 9.8 and 20 mM MgCl2. Then 10 μL of 100 mM pnitrophenyl phosphate (>99%, Roth AG) was spiked into the sample in a 96-well plate and incubated at 37 °C. Absorption was monitored at 405 nm and the activity (in IU, defined as 1 IU = 1 μmol pnitrophenol per min) calculated via the kinetics method from the slope of the absorption values. For calibration of the absorption readout, a standard curve was measured using calibration solutions of 10 mM p-nitrophenol (N7660, Sigma) at equivalent volumes.