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What does glomerular filtration rate (GFR) tell us in regards to the kidneys?

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What does glomerular filtration rate (GFR) tell us about the kidneys?

Patients with kidney disease may experience many alternative symptoms or no symptoms in any respect. Some people experience renal symptoms akin to hematuria or flank pain; others with edema, hypertension or uremia; and for many individuals, laboratory tests will show elevated serum creatinine or an abnormal urine test result (Inker and Perrone, 2021). Once diagnosed, the degree of kidney disease is assessed and the underlying disease is set. Estimation of glomerular filtration rate (GFR) is a key indicator of kidney function. What is GFR and what does it tell us about kidney disease?

Pathophysiology

To understand GFR, we must first understand the anatomy and physiology of the kidneys. The kidneys perform many key functions within the body (Inker and Perrone, 2021):

  • Excrete waste products akin to urea, creatinine and uric acid
  • They regulate the excretion of water and electrolytes
  • It secretes hormones akin to renin, prostaglandins and bradykinin
  • They take part in the production of red blood cells (erythropoietin)
  • They play a job within the metabolism of calcium, phosphorus and bones

Nephrons are the functioning units of the kidneys that produce urine. Each human kidney comprises roughly a million nephrons. Each nephron comprises a glomerulus in Bowman’s capsule, a proximal tubule (convoluted and straight element), an intermediate tubule (loop of Henle), a distal convoluted tubule, a communicating tubule, and cortical, outer medullary, and inner medullary collecting ducts.

Glomerular filtration rate (Inker and Perrone, 2021)

The glomeruli in each nephron filter the blood from toxins and waste products. In total, the glomeruli filter roughly 180 liters of plasma per day. GFR is an approximate indication of the amount of blood (ml) filtered per minute (min) per body surface area (1.73 m2)2) in all functioning nephrons. The normal GFR value depends upon age, gender and body size and is roughly 120 (in women) and 130 (in men) ml/min/1.73 m2. Decreased GFR may mean worsening kidney disease, progression of an underlying disease, or the event of a reversible problem akin to reduced renal perfusion attributable to lack of blood volume. A GFR test could also be needed if you could have a family history of risk aspects for kidney disease, akin to diabetes, hypertension, or kidney failure.

Stages of chronic kidney disease

GFR is a vital value used to find out the severity of chronic kidney disease (CKD). CKD is diagnosed when eGFR stays below 60 ml/min/1.73 m22 for 3 consecutive months. There are five stages of CKD.

(Levey and Inker, 2018)

ml/min/1.73 m22

1 Kidney damage within the presence of normal kidney function 90 or more 90 – 100%
2 Kidney damage with mild lack of kidney function 60 – 89 60 – 89%
3a Mild to moderate lack of kidney function 45 – 59 45 – 59%
3b Moderate to severe lack of kidney function 30 – 44 30 – 44%
4 Severe lack of kidney function 15 – 29 15 – 29%
5 Kidney failure Less than 15 Less than 15%

Calculating accurate GFR is a fancy process and too burdensome to perform on the bedside. Instead, GFR is often estimated from serum markers. Use GFR as a tool to assist recognize and manage kidney disease.

Inker, L. A., & Perrone, R. D. (2021, October 4). Assessment of kidney function. Current. https://www.uptodate.com/contents/assessment-of-kidney-function

Levey, A. S., and Inker, L. A. (2018). Definition and severity of chronic kidney disease in adults. Current. Downloaded from https://www.uptodate.com/contents/definition-and-staging-of-chronic-kidney-disease-in-adults

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