Measurement error and repeatability of weighing scales: implications for heart failure care

Body weight guides decongestion in acute decompensated heart failure and is frequently used as a trial outcome, but scale performance in routine care is insufficiently characterized. To assess how closely household and medical scales measured known reference loads, how much measurements varied between scales, and how consistently scales performed during repeated measurements and across measurement days. We tested 37 digital scales (29 household and 8 medical) at two Danish hospitals using reference loads from 25 to 125 kg. Each scale underwent three measurements per load on two days. Household scales showed modest mean measurement error at most reference loads, but variability between devices increased and repeated and day-to-day measurements became less consistent as load increased. At 125 kg, median absolute measurement error was 1.13 kg on Day 1 and 1.43 kg on Day 2, while between-scale standard deviations (SDs) were 2.30 kg and 6.27 kg, respectively. Medical scales showed mean errors of 0.00-0.25 kg, between-scale SDs of 0.00-0.12 kg, consistently high repeatability, and small day-to-day differences. Among the scales tested, household scales showed modest mean measurement error but substantial between-scale variability and poorer repeatability at higher loads, whereas medical scales performed consistently. These findings support preferential use of medical scales in hospitals and use of the same device for serial measurements when household scales are used.