The difference between cystatin C- and creatinine-based estimated glomerular filtration rate and survival in amyotrophic lateral sclerosis: a population-based cohort study

We investigated the relationship between cystatin C- and creatinine-based estimated glomerular filtration rate (eGFRdiff) and amyotrophic lateral sclerosis (ALS) outcomes. We enrolled ALS patients diagnosed between January 2014 and December 2019. Experienced neurologists followed up the participants until January 2022. Absolute difference between eGFR (eGFRabdiff) and relative difference between eGFR (eGFRrediff) were obtained. Cox proportional hazard models were used to evaluate the relationship between eGFRdiff and ALS survival. Negative eGFRabdiff were common in the patients (74.7%). For each SD increase of eGFRabdiff, the risk of poor prognosis for ALS patients decreased by 1.9% (HR, 0.981; 95% CI, 0.973–0.989). For each 10% increment in eGFRrediff, the risk of poor prognosis for ALS patients decreased by 17.7% (HR, 0.823; 95% CI, 754–0.898). We found that large eGFRdiff was associated with poor prognosis in ALS. Monitoring eGFRdiff in ALS population facilitates prognostic stratification assessment and precise management. This study explored whether differences between two kidney function tests – eGFRcys (based on cystatin C) and eGFRcr (based on creatinine) – could predict survival in amyotrophic lateral sclerosis (ALS) patients. By following patients from 2014–2022, we measured two forms of differences: eGFRabdiff (eGFRcys minus eGFRcr) and eGFRrediff (eGFRcys divided by eGFRcr). Most patients (75%) showed negative eGFRabdiff, and both eGFRabdiff and eGFRrediff were consistently linked to poorer survival outcomes – specifically, each standard increase in eGFRabdiff lowered risk by 1.9%, while each 10% increase in eGFRrediff lowered risk by 17.7%. These findings suggest that monitoring routine differences between kidney tests could help doctors better predict ALS progression, identify high-risk patients earlier, and personalize treatment approaches.