Serum amyloid A1 (SAA1) is a protein that in humans is encoded by the SAA1 gene. SAA1 is a major acute-phase protein mainly produced by hepatocytes in response to infection, tissue injury and malignancy. When released into blood circulation, SAA1 is present as an apolipoprotein associated with high-density lipoprotein (HDL). SAA1 is a major precursor of amyloid A (AA), the deposit of which leads to inflammatory amyloidosis.

Serum amyloid A (SAA) and C reactive protein (CRP) are the most sensitive acute phase proteins in plasma. Plasma concentrations of these proteins increase up to 1000-fold of their physiological levels in response to inflammation. In plasma both SAA and CRP are believed to be derived mostly from the liver. Hepatocytes secrete these proteins by the induction of inflammation related cytokines such as tumour necrosis factor α, interleukin 1, and interleukin 6. Although some differences in cytokine regulation by hepatocytes has been noted between SAA and CRP, clinical observations suggest that plasma concentrations of these two proteins are highly correlated with each other in most inflammatory diseases.