Elevated ALP - Causes by Source

Hepatobiliary Causes

• Primary biliary cholangitis (PBC) - one of the classic causes; anti-mitochondrial antibody (AMA) is positive
• Primary sclerosing cholangitis (PSC)
• Secondary sclerosing cholangitis
• Biliary obstruction - choledocholithiasis, stricture, bile duct carcinoma
• Drug-induced cholestasis - phenothiazines, anabolic steroids, oral contraceptives, erythromycin, chlorpromazine, and many others
• Intrahepatic cholestasis of pregnancy
• AIDS cholangiopathy - due to CMV or Cryptosporidium infection

• Hepatic metastases - ALP is the most sensitive hepatic chemistry marker for metastatic disease
• Primary liver tumors
• Amyloidosis with hepatic involvement
• Sarcoidosis of the liver
• Granulomatous infections - tuberculosis, fungal infections
• Langerhans cell histiocytosis
• Extramedullary hematopoiesis

• Viral hepatitis - mild elevation (<3x) possible in any hepatitis
• Alcoholic hepatitis / steatohepatitis - rarely, values are greatly elevated
• Cirrhosis
• Congestive heart failure (hepatic congestion)
• Sepsis - can produce a cholestatic picture
• Liver transplant rejection
• Hodgkin's disease with liver involvement
• Diabetes mellitus (mild isolated elevation)
• Hyperthyroidism

Bone Causes (bone ALP elevated, GGT normal)

Physiological Elevations (non-pathological)

• Pregnancy (3rd trimester) - placental isoenzyme floods the bloodstream
• Childhood and adolescence - bone ALP is elevated due to rapid bone growth; values are up to twice adult levels
• Post-menopausal women - ALP rises gradually; a healthy 65-year-old woman has ALP ~50% higher than a healthy 30-year-old
• Blood groups O and B - after a fatty meal, intestinal ALP is released into blood; check ALP in the fasting state to avoid this
• Mild age-related rise in both sexes after age 60 (up to 1-1.5x normal)

Less Common / Miscellaneous

• Benign familial hyperphosphatasemia - persistent elevation of intestinal isoenzyme
• Congestive heart failure
• Renal cell carcinoma (ectopic ALP production)
• Hyperthyroidism (increased bone turnover)

Diagnostic Approach

What LOWERS ALP (for contrast)

• Hypophosphatasia (inborn enzyme deficiency)
• Wilson's disease (copper displaces zinc cofactor)
• Malnutrition
• Hemolysis (falsely lowers measured value)
• Theophylline and estrogen therapy

Genetic Correlations with ALP

1. Hypophosphatasia - ALPL Gene (LOW ALP)

• Gene: ALPL on chromosome 1p36 - encodes tissue-nonspecific ALP (TNSALP)
• Inheritance: Autosomal recessive (severe forms) or autosomal dominant (mild forms)
• Effect: Loss-of-function mutations - ALP is markedly LOW
• Substrates accumulate: inorganic pyrophosphate (PPi), phosphoethanolamine, pyridoxal-5'-phosphate
• Results in defective bone mineralization - mimics rickets/osteomalacia
• A low ALP + elevated vitamin B6 + bone disease = classic hypophosphatasia
• Tietz Textbook of Laboratory Medicine

2. Paget's Disease of Bone - SQSTM1 / TNFRSF11A (HIGH ALP)

• Genes: Mutations in SQSTM1 (sequestosome-1/p62) most common; also TNFRSF11A (RANK), VCP, ZNF687
• Inheritance: Autosomal dominant with variable penetrance; ~15-40% of cases are familial
• Effect: Unregulated osteoclast activity followed by chaotic osteoblast over-reaction - ALP can be 10-25x normal (one of the highest ALP elevations seen in any condition)
• Bone and liver ALP isoenzymes share a single gene and differ only by post-translational glycosylation, so fractionation is needed to confirm bone origin
• Goldman-Cecil Medicine; Henry's Clinical Diagnosis

3. Progressive Familial Intrahepatic Cholestasis (PFIC) - ATP8B1, ABCB11 (PARADOXICALLY NORMAL/LOW GGT despite HIGH ALP)

• Key point: In PFIC types 1 and 2, serum ALP is elevated (cholestatic liver disease) but GGT is paradoxically normal - because reduced bile salt concentration keeps GGT anchored to the canalicular membrane rather than leaking into serum
• This is clinically important: the usual rule "elevated GGT = hepatic source of ALP" does not apply here
• Yamada's Textbook of Gastroenterology

4. Wilson's Disease - ATP7B Gene (LOW ALP)

• Gene: ATP7B on chromosome 13q14 - encodes a copper-transporting ATPase
• Inheritance: Autosomal recessive
• Effect: ALP is paradoxically LOW (or normal) despite fulminant hepatic failure
• Mechanism: excess copper displaces zinc (the ALP cofactor), inactivating the enzyme
• The triad of acute liver failure + hemolytic anemia + low ALP is highly characteristic of acute Wilson's disease
• Yamada's Textbook of Gastroenterology

5. Primary Biliary Cholangitis (PBC) - HLA & Immune Genes (HIGH ALP)

• Genetic susceptibility tied to HLA-DR8 and immune-regulatory loci (IL12A, IL12RB2, STAT4, IRF5)
• Autoimmune destruction of intrahepatic bile ducts causes cholestasis
• ALP is typically 4-10x normal and is often the first and only abnormal LFT
• Anti-mitochondrial antibody (AMA) against the pyruvate dehydrogenase complex (PDC-E2) is the hallmark

6. Primary Sclerosing Cholangitis (PSC) - HLA-B8/DR3 (HIGH ALP)

• Strong association with HLA-B8, HLA-DR3, HLA-DRw52a
• Also linked to IL2, IL2RA loci
• High association with IBD (especially ulcerative colitis) - shared genetic susceptibility
• ALP elevated as a dominant feature of the cholestatic pattern

7. Hereditary Hemochromatosis - HFE Gene (HIGH ALP - secondary)

• Gene: HFE - C282Y and H63D mutations (chromosome 6p21)
• Inheritance: Autosomal recessive
• Iron overload causes hepatic fibrosis/cirrhosis and eventually cholestasis
• ALP elevation is secondary to liver infiltration and damage

8. Alpha-1 Antitrypsin Deficiency - SERPINA1 Gene (HIGH ALP)

• Gene: SERPINA1 - PiZZ phenotype is most severe
• Inheritance: Autosomal codominant
• Misfolded Z-protein accumulates in hepatocytes causing progressive liver disease
• ALP elevation reflects intrahepatic cholestasis, especially in neonatal period

9. Blood Group Genes (ABO) - Physiological

• Blood groups O and B (glycosyltransferase gene variants on chromosome 9q34)
• Release intestinal ALP isoenzyme after fatty meals for up to 12 hours
• This is a normal physiological variant, not pathological - always check ALP in the fasting state

Summary Table