Short-term biological variability of, and breed differences in, N-terminal pro-B-type natriuretic peptide (NTproBNP) that might influence interpretation of test results have been reported. This study aimed to assess the variability of plasma NTproBNP measurements over 8 months in healthy Labrador Retrievers, and also to investigate correlation between urine NTproBNP:creatinine ratio (UBNP-C) and plasma NTproBNP concentration.

Fifty-three Labrador Retrievers (median age 5.2 years, range 2.3–8.2 years) were maintained at WALTHAM in housing and with study procedures complying with the Animals (Scientific Procedures) Act 1986 (UK), and residual samples were used for this study. All dogs were healthy and echocardiographically normal. Serial sampling of fasted plasma and urine were performed (weeks 0, 8, 16, 24, and 32) including assessment of NTproBNP, measured in residual plasma and urine (latter indexed to creatinine).

The log₁₀ (plasma NTproBNP) was analysed by a linear mixed model (REML) to allow for repeated measures on each dog over time, with a random effect of dog and categorical fixed effects of diet, week, and their interaction. Changes from baseline to weeks 8, 16, 24, and 32, and the changes between each week, were analysed. Percentage variability from baseline of plasma NTproBNP was calculated. An average plasma NTproBNP for each dog over the 5 study points was calculated (AV-BNP). NTproBNP standard deviation (SD-BNP) was also assessed. Spearman's correlation analysis was performed to investigate correlation between UBNP-C and plasma NTproBNP.

Clinically important values in plasma NTproBNP were detected, with wide intra-individual variability (70–130%). There was no association between percentage variability of plasma NTproBNP, SD-BNP or AV-BNP and any other measured variable, other than a mild, positive correlation between age and AV-BNP (r=0.429, p=0.002). A weak positive correlation between UBNP-C and plasma NTproBNP (rho 0.368, p<0.001).

Plasma NTproBNP measurements in clinically healthy Labradors are frequently outside laboratory reference intervals, creating false positive tests, compounded by significant measurement variability. UBNP-C has questionable clinical utility; further studies are necessary to validate this measurement.

Disclosures

Disclosures to report.

Allaway, Harrison, and Colyer are employees of WALTHAM, a division of Mars Petcare Ltd. Reduced cardiac biomarker fees were provided by IDEXX Laboratories for this study.