eGFR: The Best Test to Detect Early Kidney Damage

The Biomarker Handbook is a curated series that seeks to provide readers with insights on each biomarker we cover in our blood test packages and its relation to our body.

Your kidneys are vital organs located beneath the rib cage on either side of the spine. They filter waste products and extra fluid from our body to keep us healthy in fluid and electrolyte balance by excreting them in the form of urine. The kidneys do this through the glomeruli, which are complex structures with clusters of looping arteries around excreting ducts. This unit of glomeruli and excreting ducts form the nephron, the basic functional unit of the kidney.

The kidneys, through these clusters of looping arteries, filter about 100 to 140 liters of blood, and excrete 1 to 2 liters of urine each day. Not only are the kidneys indispensable for fluid balance and waste excretion, they also work extremely hard each day. It is vital that you care for them throughout your whole life.

Diseases that commonly lead to kidney damage typically affect the glomeruli, losing then their ability to filtrate the blood adequately. Therefore, a test was developed to calculate an estimated glomerular filtration rate (eGFR). This equation involves the person’s gender, age, plasma creatinine, and ethnicity.

Why is eGFR Biomarker So Important?

Assessing your GFR is of utmost importance to evaluate the kidney’s health, to correct the dose of drugs in people with kidney disease, and to detect chronic kidney disease (CKD- or gradual loss of kidney function) in its early stages and closely monitor their disease progress.

CKD is directly linked to eGFR in such as way that clinically the 5 stages of CKD (from mild kidney damage to end-stage kidney disease) are defined by the eGFR values (see below).

Progressive kidney damage or kidney failure can be prevented through early detection and treatment of CKD.

What Are the Causes of Kidney Disease?

Glomerulonephritis, hypertension, and type 2 diabetes are the three leading causes of kidney damage and CKD in Asia. Other less common causes include kidney tubular obstruction (stones), inherited kidney diseases, other types of nephritis, infection.

eGFR is often used as a screening tool in many metabolic panels, as not only is it a sensitive tool to detect early kidney disease (remember symptoms tend to appear in the later stages), but it can directly provide the severity by the exact staging of the CKD. It doesn’t diagnose the underlying cause of the CKD, and your doctor will order more tests once eGFR is abnormal to find the cause and treat it, to prevent progressing damage to the kidneys.

Chronic kidney disease is rapidly becoming more common worldwide, with a high global prevalence of 11 to 13%, with the majority in stage 3. Asia has one of the largest population of CKD affected individuals, and since the disease has little or no symptoms in the early stages, the real prevalence is likely much higher.

Signs and Symptoms of Kidney Disease

Typically in the early stages of kidney disease, the kidneys have the physiological ability to maintain the GFR because the remaining healthy and functioning nephrons compensate for the destroyed ones. This adaptability of the nephron allows for continued normal clearance of plasma solutes. However, in time, the over-functioning nephrons also become damaged due to the excess workload, resulting in further renal dysfunction. Furthermore, delayed diagnosis means that the underlying disease (hypertension, diabetes or glomerulonephritis) continue to damage the remaining nephrons.

Due to the nephron’s capacity of adaptation and the asymptomatic nature of the disease, CKD is not frequently detected until its later development, resulting in lost opportunities for prevention. However, late signs and symptoms of kidney disease can include:

– Hyporexia (appetite loss)

– Oliguria (decrease in urination)

– Anuria (cease of urination)

– Lower extremities edema (swelling)

– Shortness of breath

– Mental confusion

– Sleep disturbances

– Fatigue and weakness

What Does Your GFR Result Mean?

CKD is classified into 5 stages according to the eGFR value (ml/min/1.73 m2 ):

  • Stage 1 CKD with normal or high GFR (eGFR > 90 mL/min)
  • Stage 2 or CKD (eGFR = 60-89 mL/min)
  • Stage 3A or moderate CKD (eGFR = 45-59 mL/min)
  • Stage 3B moderate CKD (eGFR = 30-44 mL/min)
  • Stage 4 or severe CKD (eGFR = 15-30 mL/min)
  • Stage 5 or end-stage renal failure (eGFR < 15 mL/min) requiring dialysis

A decrease in GFR to <60 mL/min/1.73 m2 for 3 or more months is a diagnostic criterion for CKD and is associated with a greater risk of fatal and nonfatal outcomes.

Are There Any Treatments Available?

Treatment of CKD is multifaceted, and always under the supervision of a health-care team.

To prevent further kidney damage, prompt diagnosis and management of underlying conditions and comorbidities such as hypertension or diabetes are vital. Maintaining adequate levels of blood pressure and blood sugar is of utmost importance.

Reduce workload of the kidneys by avoiding all kidney-toxic lifestyle decisions.

– Ceasing smoking.

– Adequate intake of vitamin supplements, calcium, and iron.

– Avoiding sodium (salt) excess.

– Limiting the intake of potassium-rich foods.

– Stopping the intake of nephrotoxic drugs.

Cases where the individual has end-stage kidney disease, treatment options also include renal replacement therapy (RRT) which involves renal transplantation and peritoneal dialysis or haemodialysis to maintain fluid and electrolyte balance.

Are There Other Studies to Help Test the Kidney Function?

Your doctor may order tests to diagnose the underlying cause of the CKD, and also tests to assess the degree of kidney damage including but not exclusive to:

– Urinalysis

– Creatinine (Cr), either serum Cr (blood) or Cr clearance (urine)

– Blood Urea Nitrogen (BUN)

– Cystatin C

– Diabetic workup

– Inflammatory markers (CRP)

– Autoimmune disease markers

– Calcium, uric acid, phosphate, and full electrolytes and minerals

Imaging studies such as kidney ultrasound, MRI, CT scan, or even a kidney biopsy might be necessary as well.

Kidney disease is becoming a worldwide common issue, with more individuals being diagnosed every day. People with type 2 diabetes and hypertension are considered to be the population with the highest risk for kidney damage.

The eGFR does not only help evaluate the kidney’s health, but it can also be used to adjust medications in already diagnosed individuals, therefore decreasing the rates of morbidity and mortality usually associated with this condition.

Early diagnosis and treatment help slow down the deterioration of kidney functions, and supervision by a multidisciplinary health-care team is always recommended. End-stage kidney disease requires lifelong 3 to 4 weekly dialysis, let’s avoid it at all costs. Take charge of your kidney health and test your eGFR regularly.

If you want to find out more about how to properly care for your kidneys, take a look at our lifestyle article here!

Interested in other biomarkers? Check out the rest of The Biomarker Handbook.

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