Kidney filtration is a complex process involving multiple structures and discrete stages wherein nutrients are continuously filtered out and into the body. With a procedure that happens ceaselessly, determining how to measure kidney health to assess whether daily habits need changing can be challenging. Understanding kidney function early is critical because chronic kidney disease is largely asymptomatic in its initial stages, with noticeable symptoms often failing to appear until up to 90% of kidney function has already been lost1. Without proactive screening by the time we realise something is wrong, death is not far behind. This urgent diagnostic challenge is where the estimated Glomerular Filtration Rate (eGFR) becomes essential.
Glomerular filtration rate (GFR/ mGFR) was first introduced by Ludwig in 1844; however measurement of the filtrate was discovered 100 years after by Rehberg in 19262,3. And with further experimentation to determine the best biomarker to measure GFR, inulin was elected as the most optimum marker by Richards AN, Westfall BB and Bott PA. It is due to their work that the modern gold standard regarding mGFR was established, with inulin being used throughout it all4.
That is how GFR/mGFR works, eGFR on the other hand is calculated by measuring creatinine levels in the blood and applying a standardized mathematical formula to capture overall filtration capacity. Although eGFR and mGFR employ distinct procedures and have different terminology, they serve the same purpose of finding the filtration rate in order to evaluate kidney health.
Every medical assessment has inherent limitations; eGFR can occasionally be imprecise and carries a known margin of error when compared to a true mGFR5. At the same time, directly measuring GFR is logistically demanding, requiring patients to remain under continuous clinical surveillance for an entire day, a commitment many cannot afford, alongside the fact that raw inulin is notoriously difficult to procure globally6. Nonetheless, studies have concluded and affirm that eGFR remains a dependable estimate, until a less time-consuming and non-invasive method is developed3. Fundamentally, eGFR suffices, because having an accessible tool that provides advance warning of kidney failure is far better than having no point of reference at all.
Your kidneys are vital organs, and in this life you are only granted one pair to last a lifetime. Taking proactive actions to care for them is essential for long-term health, take the decision to treat your kidneys well and get screened today.
References:
1National Kidney Foundation. (2023). Kidney failure. In National Kidney Foundation. https://www.kidney.org/kidney-topics/kidney-failure
2Glassock, R. J., & Winearls, C. (2024). Ageing and the glomerular filtration rate: Truths and consequences. Transactions of the American Clinical and Climatological Association, 120, 419. https://pmc.ncbi.nlm.nih.gov/articles/PMC2744545/
3Smith HW. New York: Oxford University Press; 1951. The Kidney: Structure and Function in Health and Disease; p. 41
4Richards AN, Westfall BB, Bott PA. Renal excretion of inulin, creatinine and xylose in normal dogs. Proc Soc Exp Biol Med. 1934;73:32–35.
5Levey, A. S., Coresh, J., Hocine Tighiouart, Greene, T., & Inker, L. A. (2019). Strengths and limitations of estimated and measured GFR. Nature Reviews Nephrology, 15(12), 784–784. https://doi.org/10.1038/s41581-019-0213-9.
6Bjornstad P, Karger AB, Maahs DM. Measured GFR in Routine Clinical Practice-The Promise of Dried Blood Spots. Adv Chronic Kidney Dis. 2018 Jan;25(1):76-83. doi: 10.1053/j.ackd.2017.09.003. PMID: 29499891; PMCID: PMC5836491.