Increased ALP levels

Levels vary with age with isolated high levels often seen during childhood and adolescence due to the rapid velocity of bone growth and development.  Substantially isolated raised levels of ALP> 100% the upper limit of normal are due to bone causes (Pagets disease, osteomalacia, primary bone tumour, metastases) rather than hepatic or biliary pathology.

ALP is not usually raised in multiple myeloma or in osteoporosis unless there is the presence of a fracture.  The most common causes of extrahepatic cholestasis are stones or strictures in the common bile duct (uncomplicated or complicated with biliary pancreatitis or acute cholangitis), primary sclerosing cholangitis and malignancy causing obstruction (due to the presence of a neoplasm at the head of the pancreas, gallbladder or bile duct).

Intrahepatic cholestasis is usually due to primary biliary cirrhosis, primary biliary cholangitis, cholestasis of pregnancy, drug induced, alcoholic hepatitis or infiltrative diseases  (TB, sarcoidosis, lymphoma, amyloidosis).  Patients with PBC or primary biliary cholangitis usually have elevated ALP levels and normal bilirubin levels.  Mild and stably elevated ALP up to 50% ULN is often seen in the elderly and may be of bony or hepatic origin but does not require further investigation in the absence of relevant clinical findings.   Other causes of raised ALP are seen in hyperparathyroidism, renal failure, heart failure or lymphoma.  A raised ALP is a normal finding in the third trimester of pregnancy, produced by the placenta.

Low levels of ALP

Low levels are uncommon.  They may be a sign of a lack of zinc, malnutrition, pernicious anaemia, thyroid disease, Wilson disease or hypophosphatasia, a rare genetic disease that affects bones and teeth.