PTH and kidney failure: It was assumed that it detected the biologically active PTH (1–84) and avoided cross reactivity with C-fragments, and thus was referred to as the ‘intact’ PTH assay.11,12 However, subsequent studies revealed that these assays overestimated values in patients with kidney failure compared to PTH values in normal subjects because of the accumulation of N-truncated PTH fragments, the most abundant of which is 7–84 PTH.13,14 The third-generation PTH assays use a capture antibody against the C-terminal amino acids similar to the second-generation.