Gallstone Composition
Gallstones are primarily composed of cholesterol, with calcium salts (including calcium bilirubinate, calcium carbonate, and calcium phosphate) and bilirubin as additional major components.
Primary Components
The composition of gallstones varies by stone type, but the main constituents include:
Cholesterol Stones
- Cholesterol is the predominant component in the majority of gallstones 1
- These stones are amenable to nonsurgical dissolution therapy when they are primarily cholesterol and less than 1.5 cm in diameter 1
- Cholesterol stones also contain smaller amounts of phospholipids, fatty acids, and proteins 2
Pigment Stones
Pigment stones contain:
- Calcium bilirubinate as the primary component
- Calcium carbonate
- Calcium phosphate (hydroxyapatite)
- Higher concentrations of bile acids, soluble proteins, and various electrolytes (sodium, potassium, chloride, magnesium) 2, 3
Mixed Stones
Mixed stones represent a combination of both cholesterol and pigment components, with varying proportions of:
- Cholesterol
- Bilirubin
- Calcium salts
- Triglycerides and fatty acids 2
Additional Minor Components
Research has identified numerous trace components present in all gallstone types 2:
- Phospholipids
- Triglycerides
- Bile acids
- Fatty acids (esterified)
- Soluble proteins
- Minerals: calcium, magnesium, iron, copper, sodium, potassium
- Inorganic phosphate
- Oxalate
- Chlorides
Clinical Implications
The composition directly determines treatment options. Nonsurgical dissolution therapy with oral bile acids works by solubilizing cholesterol, making it effective only for cholesterol-predominant stones less than 1.5 cm 1. This limitation means only approximately 20% of cholecystectomy candidates would be suitable for medical dissolution therapy 1.
Calcium content is particularly important in gallstone pathogenesis 4. Precipitated calcium salts are major components of pigment stones and are frequently found in the centers and rims of cholesterol stones, playing a crucial role in stone nucleation and growth.
Important Caveat
While cholesterol is the major component across most gallstone types, the relative proportions of lipids, cations, and anions differ significantly between stone types, indicating distinct mechanisms of formation 2. This compositional heterogeneity explains why surgical removal (cholecystectomy) remains the definitive treatment, as it is "not limited by the size or composition of the gallstones" 1.