| Summary: | Abstract Introduction Serum thrombopoietin (THPO) is a biomarker of Alzheimer's disease (AD) and the latent dementia phenotype, “δ”. Both associations may be specific to non‐Hispanic whites (NHW), not Mexican‐Americans (MA). In this analysis, we examine ethnicity's effect on THPO's association with change in δ scores, in the Texas Alzheimer's Research and Care Consortium (TARCC). Methods We constructed an ethnicity equivalent δ homolog (“dEQ”) among n = 1113 MA and n = 1958 NHW. dEQ was output as a composite “dEQ‐score” for each of five annual TARCC waves. Those composites were used as indicators of a latent growth curve (LGC). The mean dEQ intercept (idEQ) and slope (ΔdEQ) were estimated in a random subset of N = 1528 participants and replicated in the remainder (n = 1544). THPO was regressed onto idEQ and ΔdEQ. Those associations were tested separately in MA and NHW. Results dEQ correlated strongly with CDR‐SB (r = 0.99, P < .001) and achieved high AUCs for AD diagnosis at each wave (range = 0.95–0.99). THPO was significantly associated with idEQ but not ΔdEQ. That effect was observed in NHW only. In MA, THPO had no associations with either idEQ or ΔdEQ. Discussion We confirm THPO's ethnicity‐specific association with δ in NHW. It is further clarified that this association is specific to δ's intercept and not its slope. This analysis provides a model for how dementia's specific serum biomarkers can be characterized.
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