Methods and kits are provided for amplifying and detecting misfolded proteins from samples, for example, from patients having Alzheimer's Disease, Parkinson's Disease, and the like. For example, a method for determining a presence of soluble, misfolded protein in a sample may include contacting the sample with a monomeric, folded protein to form an incubation mixture; conducting an incubation cycle two or more times effective to form an amplified portion of misfolded protein; incubating the incubation mixture effective to cause misfolding and/or aggregation of at least a portion of the monomeric, folded protein; physically disrupting the incubation mixture effective to break up at least a portion of any protein aggregate present; and determining the presence of the soluble, misfolded protein in the sample by detecting at least a portion of the soluble, misfolded protein. The monomeric, folded protein and the soluble, misfolded protein may exclude prion protein (PrP) and isoforms thereof.