Immunoreactive calcitonin in cerebrospinal fluid of man.

We have detected immunoreactive calcitonin (iCT) in the cerebrospinal fluid (CSF) of normal individuals. Using an antibody with midportion recognition, the mean +/- S.D. of the cerebrospinal iCT in 27 normal subjects was 28 +/- 14 pg/ml. The mean serum iCT was 89 +/- 68 pg/ml, the CSF/serum distribution ratio being 0.31. There were no significant correlations between CSF iCT or serum iCT and the calcium, magnesium, phosphate, sodium, potassium or chloride in the CSF or serum. Although there was a trend for serum iCT values to be related to CSF iCT values, it did not attain statistical significance. The demonstration that the CSF contains iCT may have important physiologic implications, and its measurement offers a useful parameter to study its effects on calcium metabolism and/or other aspects of brain function.