What are the characteristic blood test abnormalities you would see with hypophasphatasia (HPP)?

Patients with hypophasphatasia (HPP) will have blood tests that show abnormally low alkaline phosphatase (ALP), increased levels of ALP breakdown products like pyrophosphates and increased levels of calcium in the blood.

Low alkaline phosphatase in the blood:

In the disease hypophasphatasia (HPP), the enzyme alkaline phosphatase (ALP) does not function properly. Therefore, ALP levels will be low. It is important to note that ALP varies by age and sex. Particularly in childhood, ALP levels are high so someone with hypophosphatasia may actually have what appear to be "normal" ALP levels but are actually low for their age.

Increased levels of pyrophosphate in the blood and urine:

Normally, the enzyme ALP degrades pyrophosphates like pyridoxal-5'-phosphate. In HPP, this enzyme ALP does not function so pyrophosphate levels are elevated in the blood.

Increased calcium levels in the blood:

ALP is allows bones in the body to reabsorb calcium in the blood to make new bone. Since ALP does not function, the bones cannot use the calcium circulating in the blood. Thus, you may see higher than normal calcium levels in the blood. However, there are several different causes for high calcium levels in the blood so this finding is not specific to HPP.