Gfr

Glomerular Filtration Rate
Synonyms	N/A
Pronounce	N/A
Specialty	N/A
Symptoms
Complications	Chronic kidney disease, Acute kidney injury
Onset
Duration
Types	N/A
Causes
Risks	Hypertension, Diabetes mellitus, Age
Diagnosis	Blood test, Urine test
Differential diagnosis	N/A
Prevention	N/A
Treatment
Medication
Prognosis
Frequency
Deaths	N/A

The glomerular filtration rate (GFR) is a test used to check how well the kidneys are working. Specifically, it estimates how much blood passes through the glomeruli each minute. Glomeruli are the tiny filters in the kidneys that filter waste from the blood.

Physiology

The GFR is a measure of the function of the nephron, the basic structural and functional unit of the kidney. Each nephron contains a glomerulus, where blood filtration begins. The GFR is determined by the balance of hydrostatic and oncotic pressures across the glomerular capillaries, as well as the permeability of the glomerular filtration barrier.

Factors Affecting GFR

Several factors can influence the GFR, including:

• Blood pressure: Adequate blood pressure is necessary to maintain the filtration pressure in the glomeruli.
• Plasma protein concentration: Changes in plasma protein levels can affect oncotic pressure and thus GFR.
• Renal blood flow: The amount of blood flowing to the kidneys directly affects GFR.
• Age: GFR naturally decreases with age.
• Disease states: Conditions such as diabetes mellitus and hypertension can damage the glomeruli and reduce GFR.

Measurement

GFR can be measured directly or estimated using various formulas. Direct measurement involves the use of substances such as inulin, which is filtered by the glomeruli but not reabsorbed or secreted by the renal tubules. However, this method is complex and not commonly used in clinical practice.

Estimated GFR (eGFR)

In clinical practice, GFR is often estimated using serum creatinine levels and formulas such as the Cockcroft-Gault equation, the Modification of Diet in Renal Disease (MDRD) Study equation, and the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation. These formulas take into account factors such as age, sex, and body size.

Clinical Significance

GFR is a crucial indicator of kidney function. It is used to:

• Diagnose and stage chronic kidney disease (CKD).
• Monitor the progression of kidney disease.
• Guide the dosing of medications that are excreted by the kidneys.

Chronic Kidney Disease Staging

CKD is classified into 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 3a: GFR 45-59 mL/min/1.73 m² (mild to moderate decrease)
• Stage 3b: GFR 30-44 mL/min/1.73 m² (moderate to severe decrease)
• 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 result from damage to the glomeruli, reduced renal blood flow, or obstruction of the urinary tract. Common causes of reduced GFR include:

• Diabetic nephropathy
• Hypertensive nephrosclerosis
• Glomerulonephritis
• Polycystic kidney disease

Management

Management of conditions affecting GFR involves addressing the underlying cause, controlling blood pressure, and managing blood glucose levels in diabetic patients. In advanced CKD, dialysis or kidney transplantation may be necessary.

See Also

• Kidney function tests
• Renal physiology
• Nephrology

External Links

• Kidney Disease Outcomes Quality Initiative (KDOQI) Guidelines