Particle counting immunoassay of S100 protein in serum. Possible relevance in tumors and ischemic disorders of the central nervous system.

S100 protein (S100) was assayed by particle counting immunoassay in serum samples from 50 healthy individuals, 325 patients with various neurological disorders, and 20 patients with malignant melanoma. The detection limit for this protein was 0.3 microgram/L. We detected none in healthy individuals or in 50 patients with multiple sclerosis, 23 with dementia, or 20 with meningitis. S100 was detectable in serum of only a few patients with meningoradiculitis (2/20), peripheral neuropathy (2/30), encephalitis (1/14), Guillain-Barré syndrome (1/25), or AIDS (2/20). In contrast, we observed high concentrations in 29 of 75 patients with tumors of the central nervous system, especially in meningioma (6/9), glioblastoma (9/23), and neurinoma (5/5). Values for S100 were mainly abnormally high (greater than 0.3 microgram/L) in serum from patients with cerebrovascular disorders (43/48) or with metastases of melanoma (9/11).