What is the definition and quantification of hyperfiltration in the kidney?

From the Guidelines

Hyperfiltration in the kidney is defined as an abnormally elevated glomerular filtration rate (GFR) above normal physiological levels, typically quantified as a GFR exceeding 120-140 mL/min/1.73m² in adults. This phenomenon can be measured through standard GFR assessment methods including creatinine clearance tests, estimated GFR calculations using serum creatinine (eGFR), or more precise measurements using inulin or iothalamate clearance 1. The underlying mechanism involves increased intraglomerular pressure due to afferent arteriolar dilation and/or efferent arteriolar constriction, which forces more blood through the glomeruli, as seen in conditions such as diabetic nephropathy 1. Key points to consider in hyperfiltration include:

• Normal GFR is approximately 130 mL/min/1.73 m2 for men and 120 mL/min/1.73 m2 for women, with a mean rate of decline of 0.75 mL/min/year 1
• Hyperfiltration can lead to glomerular damage, proteinuria, and progressive kidney function decline over time
• Identifying hyperfiltration early is important as interventions like ACE inhibitors, ARBs, SGLT2 inhibitors, or dietary protein moderation may help reduce intraglomerular pressure and potentially slow kidney disease progression 1 It is essential to note that GFR estimates can be inaccurate in non–steady-state conditions, such as diabetes (hyperfiltration), extremes of muscle mass or weight (e.g., obesity, amputees), or after surgery 1. Therefore, accurate measurement and monitoring of GFR are crucial in managing patients with hyperfiltration, and using a creatinine-based GFR estimating equation, such as CKD-EPI, is recommended 1.

From the Research

Definition of Hyperfiltration

• Hyperfiltration is defined as an increased glomerular filtration rate (GFR) above normal values 2.
• Glomerular hyperfiltration can be caused by afferent arteriolar vasodilation and/or efferent arteriolar vasoconstriction, leading to glomerular hypertension 3.
• The definition of hyperfiltration is uncertain and can be influenced by factors such as age-related decline in renal function and body surface area (BSA) correction 4.

Quantification of Hyperfiltration

• Hyperfiltration can be quantified using estimated GFR (eGFR) or measured GFR (mGFR) 5.
• The threshold for glomerular hyperfiltration (GHF) can be set to 135 mL/min/1.73 m2 for children aged > 2 years 6.
• Different formulas, such as the Cockroft-Gault (CG) formula, Modification of Diet in Renal Disease (MDRD), and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI), can be used to estimate creatinine clearance, but their performance may vary in subjects with obesity 5.
• A new formula has been proposed to improve the accuracy of estimated creatinine clearance (eCrCl) in patients with obesity: 53+0.7×(140-Age)×Weight/(96xSCr)×(0.85if female) 5.

Clinical Implications

• Hyperfiltration is associated with an increased risk of cardiovascular disease and all-cause mortality 2.
• Glomerular hyperfiltration can be a risk factor for the progression of chronic kidney disease 3.
• Early detection and diagnosis of hyperfiltration are important to prevent further kidney damage and cardiovascular disease 4, 5.