High alkaline phosphatase (ALP): causes, what it means and what to check next

• age 18+: 40.0 – 129 U/L

Often reflects bile-flow problems, liver disease, or bone turnover (including normal growth in adolescents).

Full reference table, citations and testing options: Alkaline Phosphatase biomarker page.

1. Bile-flow obstruction or cholestasis — gallstones in the bile duct, a narrowed duct, primary biliary cholangitis, primary sclerosing cholangitis; these usually raise ALP more than ALT/AST and often raise GGT and bilirubin with it
2. Medications that slow bile flow or irritate the liver — amoxicillin-clavulanate, anabolic steroids, estrogens and some birth control pills, antiepileptics (phenytoin, carbamazepine), allopurinol, some antifungals and antidepressants
3. Fatty liver disease, alcohol-related liver disease and hepatitis — typically a modest rise alongside higher ALT and AST
4. Liver infiltration — sarcoidosis, lymphoma, abscess or cancer that has spread to the liver — often with a very high ALP and little change in the other liver enzymes
5. Bone turnover: normal growth in children and adolescents (two to three times the adult range is expected), a fracture healing over weeks, Paget's disease of bone (often several times the upper limit), vitamin D deficiency with osteomalacia, hyperparathyroidism, and cancer that has spread to bone
6. Pregnancy — the placenta makes its own ALP, and levels two to three times normal in the third trimester are expected and harmless
7. A fatty meal within a few hours of the draw in people with blood group O or B, who release an intestinal form of the enzyme; heart failure with liver congestion; an overactive thyroid; and a benign familial form
8. Transient hyperphosphatasemia — a striking but harmless rise in a young child during or after a minor viral illness that resolves within weeks

• Usually none — most high ALP results are found on routine blood work
• From the liver and bile ducts: itching (often the first symptom of cholestasis), yellowing of the skin or eyes, dark urine, pale stools, pain under the right ribs, nausea
• From bone: bone pain that is worse at night or with weight-bearing, a bone that has become warm or misshapen (Paget's), muscle weakness and aching with vitamin D deficiency, a fracture from a minor fall
• Fatigue and weight loss when a chronic liver, inflammatory or malignant process is behind it

• GGT on the same or a repeat sample — a raised GGT confirms the liver and bile ducts as the source; a normal GGT with a high ALP points to bone (a 5'-nucleotidase or ALP isoenzyme test does the same job)
• Bilirubin, ALT and AST, read as a pattern: ALP raised far more than ALT/AST is a cholestatic pattern and leads to imaging; ALT/AST raised more than ALP is a hepatocellular pattern and leads to a hepatitis and fatty-liver workup
• Right-upper-quadrant ultrasound when the source is the liver, to look for dilated bile ducts, gallstones, fatty change or a mass; MRCP or CT if the ducts are dilated or the ultrasound is unclear
• Antimitochondrial antibody (AMA) when cholestasis is confirmed and the ducts are not blocked — primary biliary cholangitis is the common autoimmune cause, particularly in middle-aged women
• For a bone source: 25-hydroxyvitamin D, calcium, phosphorus and PTH; a plain X-ray of any painful area, and a bone scan if Paget's disease or metastasis is a question
• A medication and supplement review, and a repeat after a 12-hour fast if the first sample followed a large meal
• Mild (less than 1.5 times the upper limit) and isolated: repeat in 3–6 months; if it persists, complete the liver-versus-bone workup rather than watching indefinitely

Follow-up tests available at TestWell: ALT Test (Alanine Aminotransferase) ($16.99), GGT Test (Gamma-Glutamyl Transferase) ($19.99), Calcium Test ($16.99), PTH Test (Parathyroid Hormone) ($59.99), Phosphorus Test ($16.99).