Substantial discrepancies found between estimated and measured GFR

There may be a substantial discrepancies between estimated glomerular filtration rate (eGFR) and measured glomerular filtration rate (mGFR) on an individual level, according to a cross-sectional study.

Laboratory reports that provide eGFR calculations should consider including the distribution of this uncertainty. According to the authors, renaming the eGFR as a population average GFR (or paGFR) merits further discussion. The findings are published in Annals of Internal Medicine.

GFR is the standard metric used to assess and monitor kidney function. Directly measured GFR, or mGFR, requires injecting a filtration marker and measuring plasma or urinary clearance by serial blood and urine sampling under standardized conditions is not possible for every patient. So eGFR calculated from serum creatinine is often used by clinicians to predict an mGFR. Population-level discrepancies between eGFR and mGFR are low, but individual discrepancies are much higher. It is important to understand the magnitude of these individual-level differences for clinical decision making.

Researchers from the University of Mississippi Medical Center calculated eGFR from serum creatinine alone and cystatin C and creatinine using the Chronic Kidney Disease Epidemiology Collaboration equations for 3,223 participants and compared their eGFR to their mGFR to quantify the magnitude and consequences of the individual-level differences between the two. The authors found substantial discrepancies between directly measured GFR and estimated GFR and report that these differences resulted in only approximately 50% agreement between CKD stages. Individual-level differences between the mGFR and the eGFR did not improve substantially using cystatin C.

The authors estimate that several factors contribute to these discrepancies: creatinine and cystatin C have non-GFR factors influencing their serum concentration; variability in the mGFR can result from normal physiology and measurement error from mGFR markers and technique; and as GFR estimation models the ratio of mGFR–body surface area as a function of serum markers, it incorporates errors in mGFR and errors in body surface area calculated from height and weight. According to the authors, their findings highlight the need to make direct GFR measurements available to patients who need them. They note that implementation studies are needed in this area, and research is needed to assess how the availability and use of mGFRs change clinical management.

 Interventions based on social needs may reduce hospitalizations, health care use

A randomized study of adult Medicaid patients suggests that social program-based interventions for housing, food security, and transportation may reduce inpatient admission rates by 11 percent and emergency department visits by 4 percent. However, health care savings based on these interventions may not cover the cost of social the social programs. The findings are published in Annals of Internal Medicine.

Health care-based programs assisting patients with social needs including housing, transportation, and food security are gaining interest as a strategy to improve health and avoid unnecessary health care use, but uncertainty remains about their impact. The success of programs may vary depending on factors including patient eligibility, personnel qualifications, and enrollment duration.

Researchers from Contra Costa Health Services and University of California, Berkeley School of Public Health studied adult Medicaid enrollees in Contra Costa County, CA, at elevated risk for health care to assess the population level impact of a case management program designed to address patients' social needs. The patients were randomly assigned to 12 months of social needs case management or the control group. However, only 40 percent of those assigned to the intervention program chose to engage in case management. The researchers found that the intervention programs saved $3,423,085, or 17 percent of yearly program expenses, in hospitalization costs.

The intervention also reduced total inpatient admissions by 11 percent and total emergency department visits by 4 percent. According to the authors, the observed effect on inpatient admissions, and even more pronounced reduction in avoidable admissions, may suggest that the intervention supported better management of chronic conditions. They also report that feedback from participating case managers suggested that the program helped patients build trust with the health system, resolve basic social needs, and better navigate the care landscape. The authors caution that although the interventions saved health care use, they may not save enough money to cover the cost of intervention programs.

Reference:

Tariq Shafi, Xiaoqian Zhu, Seth T. Lirette, et al; Quantifying Individual-Level Inaccuracy in Glomerular Filtration Rate Estimation: A Cross-Sectional Study. Ann Intern Med. [Epub 5 July 2022]. doi:10.7326/M22-0610