Biologic variability of cardiac troponin I in healthy dogs and dogs with different stages of myxomatous mitral valve disease using standard and high‐sensitivity immunoassays

Background Biologic variability (BV) is one aspect of interpreting changes in biomarker concentrations known to be clinically important in people with cardiac disease, but it has not been adequately addressed in dogs so far. Objectives The purpose of the study was to determineBVof cardiac troponin I (cTnI) in healthy dogs and dogs with 3 stages of myxomatous mitral valve disease (MMVD). Methods Healthy dogs and dogs with 3 stages ofMMVDwere prospectively assigned to groups based on comprehensive clinical evaluation using current guidelines. Concentrations ofcTnIwere measured hourly, daily, and weekly using standard and high‐sensitivity immunoassays. Within‐ (CVI) and between‐subject (CVG) coefficients of variability, percent reference change value (RCV), and index of individuality (IoI) were calculated. Results All 10 healthy dogs and 76/112 (68%) of samples from 28MMVDdogs hadcTnIconcentrations below the limit of detection (LOD) using a standard sensitivity immunoassay. Only 49/160 (31%) of healthy dog samples and noMMVDsamples hadcTnIbelow the high‐sensitivity immunoassayLOD. Data analysis for the high‐sensitivity immunoassay revealedCVIof 48.1%,CVGof 60.1%,RCVof 134.0%, and IoI of 0.804 in healthy dogs. InMMVDdogs,CVIwas 39.6%,CVGwas 80.7%,RCVwas 110%, and IoI was 0.494. Of allMMVDdogs, those with Stage B2 had the lowestRCVof 91%. Conclusions Biologic variability affectscTnIconcentrations in healthy dogs and dogs withMMVD. Consideration of BV may be clinically relevant when monitoring individual changes incTnIvalues, using high‐sensitivity immunoassays.