The enzyme assay using p-nitrophenylphosphate at pH 9.5 is most elevated in which condition?

The enzyme assay using p-nitrophenylphosphate at pH 9.5 is most elevated in which condition?

• A. Hyperthyroidism
• B. Osteomalacia
• C. Paget's disease
• D. Rickets

Answer: (C)

Alkaline phosphatase activity rises with osteoblastic bone formation, and using p-nitrophenyl phosphate at alkaline pH (around 9.5) directly measures that activity. In Paget's disease, there is markedly accelerated and disordered bone remodeling with greatly increased osteoblast activity, so bone-forming enzymes like alkaline phosphatase become substantially elevated. This level tends to be higher than in other bone-related conditions such as osteomalacia or rickets, where turnover is increased but not to the same extreme, and typically higher than in hyperthyroidism, where the rise is present but usually less dramatic. Therefore, the highest ALP signal from this pNPP at pH 9.5 assay points to Paget's disease.

Alkaline phosphatase activity rises with osteoblastic bone formation, and using p-nitrophenyl phosphate at alkaline pH (around 9.5) directly measures that activity. In Paget's disease, there is markedly accelerated and disordered bone remodeling with greatly increased osteoblast activity, so bone-forming enzymes like alkaline phosphatase become substantially elevated. This level tends to be higher than in other bone-related conditions such as osteomalacia or rickets, where turnover is increased but not to the same extreme, and typically higher than in hyperthyroidism, where the rise is present but usually less dramatic. Therefore, the highest ALP signal from this pNPP at pH 9.5 assay points to Paget's disease.