Alkaline phosphatase: enzyme from liver and bone; rises with bile-flow or bone turnover change.
What it is
ALP comes from liver (bile canaliculi), bone, and smaller contributions from intestine and placenta. Reported in U/L. Paediatric ranges are higher because of bone growth: adult bands do not apply to children.
Alkaline phosphatase enzymes remove phosphate groups; the blood test totals mainly liver and bone isoforms unless isoenzymes are requested. Adult UK ranges do not apply to growing children or many adolescents.
Why it matters
Raised ALP is interpreted with other liver and bone markers and your history. Patterns can relate to bile flow or bone turnover; only a clinician can diagnose the cause. Age, pregnancy, and recent fractures change expectations.
This guide is educational only and cannot diagnose you. Discuss results, especially anything outside your laboratory’s reference interval, or that does not match how you feel, with a GP or other appropriately qualified clinician.
How it affects the body
In liver, ALP rises when bile flow is impaired; in bone, osteoblast activity releases ALP during turnover and repair.
In cholestasis, ALP from biliary epithelium rises as bile flow is impaired. In bone, osteoblasts release ALP during matrix mineralisation and repair: hence rises after fractures or in high-turnover bone disease.
For athletes
Bone-stress injuries and heavy impact blocks can nudge ALP; pair with vitamin D and clinical review if bone pain persists. Not a performance KPI.
Impact athletes with bone pain need clinical assessment for stress injury; ALP is supportive at best. Check vitamin D status under guidance when bone health is in question.
