Discriminant power of combined cerebrospinal fluid tau protein and of the soluble interleukin-6 receptor complex in the diagnosis of Alzheimer's disease

Alzheimer's disease (AD) still can only be definitively diagnosed with cert ainty by examination of brain tissue. There is a great need for a noninvasi ve, sensitive and specific in vivo test for AD. We combined cerebrospinal f luid analyses of tau protein (levels were significantly increased in AD pat ients [p = 0.0001]), a putative marker of neuronal degeneration, with compo nents of the soluble interleukin-6 receptor complex (sIL-6RC: IL-6, soluble IL-6 receptor and soluble gp130), putative markers of neuroregulatory and inflammatory processes in the brain. A stepwise multivariate discriminant a nalysis revealed that tau protein and soluble gp130 (levels were significan tly reduced in AD subjects [p = 0.007]), the affinity converting and signal -transducing receptor of neuropoietic cytokines, maximized separation betwe en the investigated groups. The discriminant function predicted 23 of 25 cl inically diagnosed AD patients (sensitivity 92%) with mild to moderate deme ntia correctly as having AD. Furthermore, 17 of 19 physically and cognitive ly healthy age-matched control subjects (specificity 90%) were accurately d istinguished by this test, Later predicting with the jackknife procedure ea ch case in turn through the remaining patient group, the discriminant funct ion remained stable. Our data suggest that multivariate discriminant analys is of combined CSF tau protein and sIL-6RC components may add more certaint y to the diagnosis of AD, however, the method will need to be extended to a n independent group of patients, comparisons and control subjects to assess the true applicability. (C) 1999 Elsevier Science B.V. All rights reserved .