GFR

Detailed article on Glomerular Filtration Rate (GFR)

Glomerular Filtration Rate
Anatomy of the kidney, where GFR is measured
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Glomerular Filtration Rate (GFR) is a critical measure of kidney function that assesses how well the kidneys are filtering blood. It is an important indicator used in the diagnosis and management of chronic kidney disease (CKD) and other renal conditions.

Physiology

The kidneys are vital organs responsible for filtering waste products and excess substances from the blood, which are then excreted as urine. The functional unit of the kidney is the nephron, and each kidney contains approximately one million nephrons. The process of filtration occurs in the glomerulus, a network of capillaries located at the beginning of each nephron.

GFR is defined as the volume of fluid filtered from the glomerular capillaries into the Bowman's capsule per unit time. It is usually expressed in milliliters per minute (mL/min).

Measurement

GFR can be measured directly or estimated using various formulas. Direct measurement involves the use of inulin clearance, which is considered the gold standard but is rarely used in clinical practice due to its complexity. Instead, GFR is commonly estimated using serum creatinine levels and equations such as the Modification of Diet in Renal Disease (MDRD) study equation or the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation.

Factors Affecting GFR

Several factors can influence GFR, including:

• Age: GFR decreases with age.
• Gender: Males typically have a higher GFR than females.
• Body size: Larger individuals may have a higher GFR.
• Blood pressure: Hypertension can affect GFR.
• Diabetes: Poorly controlled diabetes can lead to decreased GFR.

Clinical Significance

GFR is a crucial parameter in the diagnosis and staging of CKD. The National Kidney Foundation classifies CKD into five stages based on GFR:

• Stage 1: GFR ≥ 90 mL/min/1.73 m² (normal or high)
• Stage 2: GFR 60-89 mL/min/1.73 m² (mildly decreased)
• Stage 3: GFR 30-59 mL/min/1.73 m² (moderately decreased)
• Stage 4: GFR 15-29 mL/min/1.73 m² (severely decreased)
• Stage 5: GFR < 15 mL/min/1.73 m² (kidney failure)

Pathophysiology

A decrease in GFR can indicate kidney damage or disease. Conditions such as glomerulonephritis, diabetic nephropathy, and hypertensive nephrosclerosis can lead to reduced GFR. Conversely, an increased GFR may occur in conditions like pregnancy or early diabetes mellitus.

Also see

• Chronic kidney disease
• Nephron
• Creatinine clearance
• Renal physiology
• Kidney function tests

External links

• National Kidney Foundation GFR Guidelines
• National Institute of Diabetes and Digestive and Kidney Diseases - GFR