Amyloid-related serum component (SAA)-Studies in acute infections, medullary thyroid carcinoma, and postsurgery. Behavior as an acute-phase reactant

Longitudinal studies of serum SAA (amyloid-related serum component) levels were done on a group of 17 patients hospitalized for acute bacterial infections, and the results were compared to another group of 24 patients undergoing elective surgical procedures. In the former, striking initial elevations were seen, resolving rapidly with therapy and clinical status; failure of response in two patients could be correlated with ongoing or recurrent infection. By contrast, the latter group manifested little variation in SAA level. Of all the acute-phase parameters tested, only the WBC (white blood cell count) could be related to variations in SAA. Levels obtained in patients and relatives of patients with the familial form of medullary carcinoma of the thyroid were generally normal. The possible significance of this finding is discussed in view of theories claiming the amyloid associated with this entity to be light-chain-related, "A" protein, or prohormone in nature. SAA was found to be present at low levels in CSF (cerebrospinal fluid), though no correlation to age could be made at the level of resolution of the radioimmunoassay. Simultaneous serum levels ranged up to 30 times the CSF levels. A small group of patients with elevated CSF levels were also noted to have acute infections, some without evidence of meningeal irritation.