eGFR level alone may tell little about true timing of dialysis initiation

The United States Renal Data System (USRDS) has often been used to study the timing of dialysis initiation, measured by estimated glomerular filtration rate (eGFR) at dialysis initiation. However, it is not clear how well this information explains the eGFR variation at dialysis initiation, nor how well eGFR serves as a measure for the timing of dialysis initiation. Researchers examined these questions using USRDS data for nearly one million patients who started dialysis between 1995 and 2012.

In their analysis, the investigators calculated the proportion of variation in eGFR at dialysis initiation that is explained by variables measured in the USRDS. Measured variables include patient-level factors (such as age and dialysis modality), facility-level factors (such as total number of patients and nurse-to-patient ratio), and county-level factors (such as unemployment rate and high school graduation rate). Measured patient-level variables explained 10.7% of the total variation in eGFR at dialysis start, and measured facility- and county-level factors explained 1.2% of the variation. However, 78.9% of patient-level variation and 9.2% of variation between facilities and counties remained unexplained.

“It is striking that so much of the variation in eGFR at dialysis initiation is not explained by variables in the USRDS,” said lead author Dr. Yun Li. “Our study showed that we need to collect different types of data to truly understand why patients start dialysis when they do.”

The fact that most of the variation in eGFR occurred at the patient level indicates that the mean eGFR at dialysis start is relatively similar across different physicians, but the eGFR of patients treated by the same physician tend to vary substantially. This suggests that the decision to start dialysis is largely determined by patient-related factors not recorded in USRDS data, such as eGFR trajectory over time, worsening nutrition or frailty, hyperkalemia, metabolic acidosis, patient/provider preference, or perceived benefits and burden of dialysis, among other factors.

Special efforts are needed to collect this data prospectively from advanced chronic kidney disease patients approaching the need for dialysis to gain a real understanding of the factors that drive decisions about when to initiate dialysis in the United States.