What this test measures
Alkaline phosphatase is a family of enzymes that work best at alkaline pH. The major sources of serum ALP are the bile-duct cells of the liver and the bone-forming cells (osteoblasts); smaller amounts come from intestine, kidney and placenta. Each tissue contributes a slightly different isoform.
Most labs report total ALP. When the source is unclear, GGT (high in liver-source ALP, normal in bone-source ALP) or fractionated ALP (bone vs liver isoenzymes) can be added.
Why it matters
ALP is one of the most useful "where is the problem" markers in clinical medicine. A high ALP with high GGT and bilirubin points to a cholestatic picture — gallstones, biliary stricture, drug cholestasis, primary biliary cholangitis. A high ALP with normal GGT but raised calcium and phosphate points to bone turnover — Paget's disease, bone metastases, healing fracture, hyperparathyroidism, vitamin D deficiency rickets (very common in Indian children).
In India, low vitamin D is extremely common, and ALP is one of the first labs to rise in vitamin D deficiency rickets/osteomalacia. ALP also normally rises in growing children/adolescents (bone source) and in late pregnancy (placental source) — labs should report age-appropriate ranges.
How to prepare
No fasting required for ALP alone. Fasting is needed if ALP is part of an LFT with lipid or glucose tests. Mention recent fractures, pregnancy, growth spurts (in adolescents), and any medications including anti-epileptics, steroids and oral contraceptives.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Alkaline Phosphatase (ALP) (U/L)[1][2] | Adults 40 – 129 · Children / adolescents much higher (age- and sex-specific) | Low ALP is uncommon — causes include malnutrition, zinc / magnesium deficiency, hypothyroidism, severe anemia, Wilson's disease, and the rare genetic disorder hypophosphatasia. | Mild rise (1–3× upper limit) — fatty liver, drug effect (anti-epileptics, OCPs, antibiotics), early biliary disease, healing fractures, vitamin D deficiency. Significant rise (3–10×) — cholestasis (stones, stricture, primary biliary cholangitis), bone disease (Paget's, bone metastases, hyperparathyroidism), late pregnancy. Very high (>10×) — Paget's disease (often spectacular), bone metastases, severe cholestasis. |
Localising a raised ALP — liver vs bone
| Pattern | GGT | Calcium / Phosphate | Likely source | Common causes |
|---|---|---|---|---|
| ↑ ALP + ↑ GGT | Raised | Usually normal | Liver / biliary | Gallstones, stricture, primary biliary cholangitis, drug cholestasis |
| ↑ ALP + normal GGT | Normal | Variable | Bone or placenta | Paget's, bone metastases, vitamin D deficiency, hyperparathyroidism, late pregnancy, growth spurt |
| ↑ ALP + ↑ bilirubin | Often raised | Normal | Biliary obstruction | Stone, stricture, head-of-pancreas mass — needs imaging |
| Very high ALP (>5×) with normal GGT | Normal | Calcium often normal | Bone | Paget's disease, healing fracture, bone metastases |
Frequently asked questions
My ALP is 250 — what could it mean?
A moderately raised ALP needs the source identified. Your doctor will look at GGT (raised = liver source; normal = bone source), bilirubin, calcium, phosphate and vitamin D. Bone source in India is most commonly vitamin D deficiency; liver source most often early cholestasis or drug effect.
Do I need to fast?
Not for ALP alone. Fasting is needed only when it is part of a Liver Function Test bundled with lipid or fasting glucose.
Why is my child's ALP "high" — is something wrong?
No. Children and adolescents have ALP values 2–3 times adult ranges because their bones are actively growing (osteoblast activity). Labs should report a paediatric reference range. A genuinely high value in a child usually means rickets (vitamin D deficiency), which is very common in India.
Does pregnancy raise ALP?
Yes. The placenta produces its own alkaline phosphatase, and ALP can be 2–3 times the upper limit of normal by the third trimester. This is normal and does not need investigation unless there are other liver chemistry abnormalities.
My ALP is high but GGT is normal — what does that mean?
It points away from a liver source and toward a bone or placental source. Common causes in adults: vitamin D deficiency, healing fracture, hyperparathyroidism, Paget's disease, or bone metastases. Your doctor will likely add a vitamin D, calcium, phosphate and PTH.
Can medications raise ALP?
Yes — anti-epileptics (phenytoin, carbamazepine), oral contraceptives, some antibiotics (amoxicillin-clavulanate), tricyclics and steroids are common offenders. Mention all medications and herbal supplements.
Should I worry about a low ALP?
Mildly low ALP is rarely concerning. Persistent low values can flag zinc / magnesium deficiency, hypothyroidism, malnutrition, or (rarely) hypophosphatasia — your doctor will pursue these only if symptoms suggest them.
Related Liver / Enzymes tests
Tests commonly ordered alongside ALKALINE PHOSPHATASE, or that help interpret an unexpected result.
Sources & references
- NIH MedlinePlus — ALP Blood Test · accessed 2026-05-30T00:00:00.000Z
- NCBI StatPearls — Alkaline Phosphatase · accessed 2026-05-30T00:00:00.000Z
- AASLD Practice Guidance — Abnormal Liver Chemistries (2017) · accessed 2026-05-30T00:00:00.000Z
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