The Effect of Reduced Kidney Function on Young Adults

Hussain, Junayd, et al. “Associations between Modest Reductions in Kidney Function and Adverse Outcomes in Young Adults: Retrospective, Population Based Cohort Study.” BMJ, vol. 381, June 2023, p. e075062, https://doi.org/10.1136/bmj-2023-075062.

Introduction: 

The kidney’s function in the body is to filter waste from the blood. Chronic kidney disease (CKD) is a condition that results in structural damage in the kidneys, which decreases their ability to function, which means that the glomerulus can no longer perform ultrafiltration, which is the process that removes toxic metabolic wastes like urea from the body and reabsorbs glucose. This function of the glomerulus (eGFR) decreases. CKD is a progressive disease but can be controlled with treatment and lifestyle modifications. The effect of age on eGFR is uncertain, which means that there is limited knowledge on how to manage and mitigate the risk of loss of kidney function in younger adults, however, younger individuals typically lose a large amount of kidney function before being diagnosed with chronic kidney disease. This study investigates the association of small reductions in eGFR with age, and consequently with adverse outcomes. These outcomes could be mortality, cardiovascular events or kidney failure. A population-based study was conducted using an age group of 18-65. 

Previous Research

Previous studies indicate that early reductions in eGFR in younger adults could lead to premature cardiovascular disease, but it has been difficult to study the outcomes of CKD in young adults due to low rates of immediate adverse outcomes specifically within their age group. The Chronic Kidney Disease Prognosis Consortium reported that there was a higher cardiovascular, end-stage kidney disease and mortality rate across a range of eGFR in younger age groups, under the age of 40. Finally, evidence from smaller groups suggests that the kidney function level above the threshold but below expected ages is associated with a higher risk of adverse outcomes in younger adults. 

Summary

The researchers obtained data for vital statistics, healthcare encounters and laboratory tests for all participants. People who had a history of kidney disease or had donated a kidney in the past 5 years were excluded. The researchers presented the data obtained using an equation known as the ‘race-free chronic kidney disease-epidemiology equation’, which ignores race but is focused entirely on creatinine level (creatinine is a chemical compound that should be filtered out in the urine by healthy kidneys), age and sex. After obtaining this information, the researchers recorded the occurrence of a cardiovascular event or kidney failure. For accuracy, they included information about sex, income and living status of the patients. Additionally, the researchers obtained urine samples to identify its composition. 

Conclusion 

The scientists found that modest reductions in estimated glomerular function were consistently associated with higher rates of adverse outcomes. The hazards were most prominent in younger adults in comparison to older groups, which means that younger adults should have more frequent monitoring of kidney function during youth to prevent chronic kidney conditions in later life. In addition to the information that was known on this topic, it was found that small kidney function reductions were associated with elevated clinical risk. Some strengths of this study were the large sample size, and consistency across analyses. There was already some literature on this topic, so the researchers were able to strengthen their findings with existing studies. However, there were some limitations as well. Firstly, some of the comorbidities such as alcoholism and smoking were self-reported, so there could have been misclassification. Additionally, the measures did not account for how chronic the kidney disease was. Still, the researchers excluded people with a history of kidney disease to increase the reliability of the study. In conclusion, this study shows the importance of frequent monitoring of kidney function in young adults.