ALP

Alkaline phosphatase is an enzyme that clips phosphate groups off molecules, and that happens in two places that have nothing to do with each other. In the wall of the bile ducts, where it helps with the drainage of bile, and in the osteoblasts, the cells that make new bone and fix minerals into it. What circulates in your blood is the sum of those two, and the number itself does not say which source it comes from. That is why you never read ALP alone. Gamma-GT does come from the bile ducts and not from bone, so high ALP with high gamma-GT is the bile drainage, and high ALP with normal gamma-GT is bone. Bilirubin confirms the bile side if it rises with it, and calcium, phosphate and vitamin D tell what is going on at the bone side. During growth, in the last months of a pregnancy and in the weeks after a fracture a high ALP is normal, because plenty of bone is being made. Your report shows ALP in U/L. Normal is about 45 to 115 U/L for a man of 19 to 50 years and 38 to 98 U/L for a woman, and in later age the band shifts slightly upward, because bone turnover increases. After a fatty meal ALP rises temporarily, especially in blood groups O and B, so have blood drawn fasting if you want to compare.

The reason ALP is interesting for anyone who wants to stay healthy sits on the bone side. With a vitamin D deficiency your gut absorbs too little calcium, and your bone cells work harder to mineralise the bone anyway; ALP then rises while the rest of your liver values are normal. A slightly raised ALP with a normal gamma-GT and a low vitamin D is thereby one of the ways a vitamin D deficiency gives itself away before it shows in your bone density. Daylight, oily fish and a supplement in winter bring it back. After the menopause ALP rises too, because bone turnover speeds up; that is the phase in which bone is lost, and strength training, protein, calcium and vitamin D are the levers. The liver side is a different story. Gallstones, a narrowing or inflammation of the bile ducts, and some medicines let ALP rise together with gamma-GT, often with bilirubin alongside and pain in the upper right of the abdomen after a fatty meal. That is a picture you recognise by the combination and that is looked into with imaging of the bile ducts. Fatty liver and alcohol, the usual reasons for a high ALT and gamma-GT, usually lift ALP only a little. A low ALP is usually nothing. It occurs with a deficiency of zinc or magnesium, which the enzyme cannot do without, with an underactive thyroid, with malnutrition, and rarely with an inherited condition in which the enzyme is missing. In anyone who eats one-sidedly or drinks a lot, zinc is the first question.

A high ALP means a bile drainage that falters or bones that are busy. Usually it is the first and rarely the last: bone turnover through growth, healing of a fracture or the menopause; bile congestion; a pregnancy; medicines; a vitamin D deficiency; and rarely a bone disease such as Paget's disease or metastases in bone. Gamma-GT is the referee: if it rises with it, it is the bile ducts, if it stays normal, it is bone. On the bone side vitamin D, calcium and phosphate say what is going on. A low ALP usually means nothing. With a deficiency of zinc or magnesium, an underactive thyroid or malnutrition the value sits lower, and in anyone who eats one-sidedly zinc is the first question. ALP belongs beside gamma-GT, and beyond that beside bilirubin on the bile side and vitamin D, calcium and phosphate on the bone side. Have blood drawn fasting, and compare over time at the same lab.