Establishment of an in-house ELISA and the reference range for serum amyloid A (SAA): Complementarity between SAA and C-reactive protein as markers of inflammation

IntroductionSerum amyloid A (SAA) and C-reactive protein (CRP) are both acute-phase reactants synthesized by the liver upon stimulation by proinflammatory cytokines reflecting both the acute and chronic inflammatory states.MethodsWe have established a one-step, sandwich ELISA on microplate for SAA using commercial antibodies for coating and detection.ResultsThis in-house ELISA has a sensitivity of 0.12 mg/l. Both within-day and between-day CVs were < 10%. The in-house assay correlated well with the commercial ELISA kit from Anogen (r = 0.95). We also established the reference range for apparently healthy Chinese. Statistically higher SAA values were found in those > 50 years old. No difference was found between genders. We found only slightly increased levels of SAA in early stage of type 2 diabetics, but highly increased levels of SAA were detected in patients with acute myocardial infarction, generally associated with intense inflammation. At the early stage of type 2 diabetes associated with low inflammation, SAA was found to be complementary to CRP in test sensitivity.ConclusionsBased on our data and reports from the literature we believe that SAA responds differently than CRP in inflammatory diseases such as in type 2 diabetes and acute myocardial infarction, and is complementary to CRP in test sensitivity.