Assessment of Inter-Instrument Reliability for Dominant Handgrip Dynamometry and Spirometry

Purpose: The aim of this study was to determine the inter-instrument reliability of different dynamometers and spirometers commonly used in clinical practice. Methods: The study involved 113 healthy volunteers across three facility sites. At each site, dominant handgrip strength (DHGS), and lung function (forced expiratory volume in one second [FEV1], forced vital capacity [FVC] and peak expiratory flow rate [PEFR]), were compared using a local and reference device. Assessments were randomized with five minutes rest between measurements. Significant differences between devices were assessed using paired t-test while relative reliability between devices was determined via intra-class correlations (ICC). Accuracy index and variability between measurements were assessed using the technical error of measurement (TEM%) and coefficient of variation (CV), respectively. Agreement between devices was determined using the Bland Altman’s plot with limits of agreement (LOA). Results: The local devices recorded significantly (p1 (3.1%-8.4%), FVC (3.1%-13%) compared to the reference devices. Good-excellent correlations (ICC=0.89-0.96), unacceptable CV (5.8-9.9%) and TEM% (6.6-9.9%), and large mean biases (3-9kg) and LOA (3-23kg) were identified between the local and reference dynamometers. Excellent correlations (ICC=0.91-0.99), and mostly unacceptable CV and TEM% were identified between the local and reference spirometers for FVC and PEFR. Compared to the reference device, all local spirometers showed unacceptable (-0.134 to -0.536 liters) and acceptable (-0.12 to 0.05 liters/second) mean biases for FVC and PEFR, respectively. Conclusion: Unacceptable inter-instrument reliability was identified between local and reference dynamometers and spirometers for measuring DHGS and all lung function indices, respectively. Across clinical settings, comparing DHGS and lung function between different brands of devices may lead to the reporting of erroneous results with corrective adjustments required for clinical practice.