Why would alkaline phosphatase level be low?

No reason.: There are ranges of "normal" for each blood test done. These may be different from one lab to other, depending on the type testing done and reliability of lab. Also, if a specific test is very abnormal and doesn't make sense clinically to the doc, it's probably lab error: just repeat it. That being said, low levels on many tests are not a problem: alk phosphatase is one. 'fagetabatit'-:).