Physical Activity Assessment in Patients With Nephrotic Syndrome and the Impact of COVID-19: A Study Using the International Physical Activity Questionnaire and Accelerometry

Background Nephrotic syndrome (NS) typically involves proteinuria, reduced levels of albumin in the blood, and swelling. It may also lead to complications, including an increased risk of thrombosis and a decline in kidney function. While pharmacological treatments are primary, physical activity (PA) may play a role in improving outcomes. However, limited data exist on PA levels in patients with NS, particularly regarding the validity of self-reported PA assessments. The COVID-19 pandemic also introduced significant lifestyle changes, potentially impacting PA and kidney function. This study aimed to (1) compare self-reported PA using the International Physical Activity Questionnaire (IPAQ) with objectively measured PA via accelerometry in patients with NS and (2) evaluate changes in PA and kidney function before and during the COVID-19 pandemic. Methods This multicenter cohort study recruited outpatients aged ≥15 years with primary NS between 2019 and 2020. Participants completed IPAQ and wore accelerometers for at least seven days. PA intensities were categorized as light PA (LPA), moderate-to-vigorous PA (MVPA), or sedentary behavior (SB). The association between IPAQ and accelerometers by activity measurement method describes the values measured for each activity intensity and shows the correlation coefficient. Kidney function was assessed using estimated glomerular filtration rate (eGFR) and urinary protein-to-creatinine ratio (UPCR). PA and kidney function were compared before (December 2019 to March 2020) and during (June to December 2020) the pandemic. Results Seventeen participants were included in the IPAQ-accelerometer comparison, and eight were analyzed for pre-pandemic versus pandemic PA changes. Across all intensity levels, IPAQ tended to underestimate PA compared to accelerometers, but this was not statistically significant (IPAQ vs. accelerometer in total PA: 56.6 vs. 652.6 min/day, p = 0.56). IPAQ showed no correlation with accelerometer-measured LPA but demonstrated a moderate correlation with MVPA. During the pandemic, MVPA decreased by 0.88% (95% CI: -5.08 to 3.33%), while SB increased by 0.59% (95% CI: -10.1% to 11.3%). Step count decreased by 810 steps/day (95% CI: -3,597 to 1,977). Kidney function remained stable, with eGFR decreasing by 4.1 mL/min/1.73 m² (p = 0.98) and UPCR increasing by 1.9 g/gCre (p = 0.17), although these changes were not statistically significant. Conclusions IPAQ underestimated PA compared to accelerometry, particularly for low-intensity activity. During the pandemic, PA decreased, while sedentary time increased, although kidney function remained stable. These findings highlight the need for objective PA measurement in patients with NS and suggest that pandemic-related lifestyle changes may have influenced PA behaviors. Further research is warranted to assess the long-term impact of PA on kidney outcomes in this population.