The kidneys play a vital role in maintaining the body’s internal environment by regulating fluid and electrolyte balance, eliminating waste products, and controlling blood pressure. Glomerular Filtration Rate (GFR) is a key parameter used to assess kidney function and is crucial in diagnosing and managing various kidney disorders.

Definition of Glomerular Filtration Rate (GFR)

GFR is a blood test measure for how much blood a person’s kidneys filter each minute. A urine Albumin test checks for albumin in urine. Albumin is a protein that can pass into the urine when the filters in the kidneys are damaged. Furthermore GFR refers to the volume of fluid that is filtered through the glomerular capillaries per unit of time. Glomeruli are tiny structures within the kidneys responsible for filtering blood and separating waste products from essential substances that need to be retained in the body. GFR is often considered the best overall indicator of kidney function, because it reflects the efficiency of the kidneys in filtering blood and removing waste.

Measuring and estimating GFR

It is important to note that normal GFR varies according to age, sex, and body size, and declines with age.

Getting an accurate GFR level is challenging because measured GFR (mGFR) is a complicated and lengthy process. This makes it impractical for both clinicians and patients. It is for this reason that healthcare professionals use a formula to estimate GFR. Often, Chronic Kidney Disease (CKD) does not have any symptoms until the later stages of the disease. This is the reason why reliable estimates of GFR are so important for identifying CKD as early as possible.

The standard way to estimate GFR is with a simple blood test that measures your creatinine levels. Creatinine is a waste product that comes from the digestion of dietary protein and the normal breakdown of muscle tissue. Aside from CKD, creatinine levels can be affected by other factors including diet; muscle (weight of a person’s muscles); malnutrition; and other chronic illnesses. In addition GFR measures how well the kidneys are filtering certain agents not produced by your body, such as: inulin, a kind of fiber that is found in some plant foods. The gold standard for GFR measurement is the inulin clearance test, where inulin, a substance freely filtered by the glomeruli and not reabsorbed or secreted, is infused into the bloodstream, and its clearance is measured. However, due to the complexity and invasiveness of this method, it is not commonly used in clinical practice.

There are a number of additional factors that can affect eGFR including the following:

• Pregnancy  
• unusual muscle mass
• cirrhosis (a disease caused by scarring in the liver)
• nephrotic syndrome (a condition caused by having too much protein in your urine),
• a past solid organ transplant
• Specific medications to avoid with kidney disease:
• Pain medications also known as nonsteroidal anti-inflammatory drugs (NSAIDs): These medications reduce blood flow to the kidneys and should be avoided. NSAIDs can also be found in many medications marketed for fevers, colds, coughs, and sleeping problems. Always check the active ingredient labeling for NSAIDs to be sure.)
• Proton pump inhibitors (PPIs): These medications are used to treat acid reflux and heartburn and it may increase the risk for kidney disease, osteoporosis, or other nutritional deficiencies. If a person is on dialysis, there may be limitations on taking these medications. Always talk to healthcare provider before taking PPIs or other acid reflux medications.
• Cholesterol medications (statins): these medications are often prescribed to help lower cholesterol levels in the blood.
• Antibiotic medications: Antibiotics, antiviral, and antifungal medications may harm the kidneys, therefore a medical healthcare provider will need to be aware of level of kidney function before prescribing these treatments.
• Diabetes medications: Diabetes is the leading cause of kidney disease. It’s important that people living with diabetes control their blood sugar levels, which may involve the use of medication.
• Antacids: Over-the-counter medications for heartburn and upset stomach can interfere with your body’s electrolyte balance, which can be problematic for people with chronic kidney disease.
• Diuretics: A diuretic is any substance that promotes diuresis, the increased production of urine. This includes forced diuresis. A diuretic tablet is sometimes, in everyday language, called a water tablet. It can cause dangerous levels of dehydration, low potassium, higher blood sugar in those individuals with diabetes and unbalanced electrolytes.
• Laxatives are commonly used to treat constipation and are generally safe when used as directed. However, chronic use of laxatives can be dangerous and affects the natural chemistry in the body. Combined with an underperforming kidney saline osmotic laxatives can be dangerous.
• Cocaine is a highly addictive drug that elevates the levels of alertness, attention, and energy, and can be extremely detrimental for the kidneys.
• Heroin is a substance that is both illegal and extremely addictive. The drug derives from opium from the poppy plant before it is refined to morphine, then further chemically modified to become heroin. With continued use over a period of time, a person abusing heroin may develop serious kidney disease.
• Herbal supplements and vitamins: Many herbal supplements contain minerals such as potassium or phosphorus that can be damaging for people with kidney disease. In general, herbal and vitamin supplements may need to be avoided if suffering from kidney disease.
• Contrast dye: Contrast dyes used in diagnostic tests such as MRIs, CT scans, or angiograms may increase your risk for kidney problems or acute kidney injury (AKI).
• High blood pressure
• Overweight/obesity
• Over the age of 60
• Family history of CKD or kidney failure: Usually, developing CKD is not due to any single reason, but because of a combination of physical, environmental, and social factors.

Later stage CKD does cause symptoms. A GFR test is important if any of the following symptoms appear:

• Urinating more often or less often than usual
• Itching
• Feeling tired
• Swelling in your arms, legs, or feet
• Muscle cramps
• Nausea and vomiting
• Loss of appetite

Foods that have a negative impact on the kidneys include the following:

• Salt: Sodium overload leads to increased blood pressure, which puts a strain on the kidneys and include the following food products:

Canned soups

Processed meats like lunch meats, hot dogs, sausages

Frozen pizza and dinners

Snack foods like chips, crackers, pretzels

Condiments like ketchup, BBQ sauce, soy sauce

Salad dressing

Pickled foods like pickles, olives, beets

Canned vegetables

• Sugar: Sugar is found in most foods, natural and processed, so it’s important to be aware of the fact that it is lurking in abundance. Fruits are a source of natural sugar, which offer many vitamins and minerals our bodies need. It’s foods with added sugars, however, that tend to be low on the nutritional value scale.

• Sodas: Carbonated and energy drinks have both been linked to the formation of kidney stones.

• Meat and dairy products: Diets high in animal protein from meats and dairy products can cause kidney damage because they can be very hard to metabolize. This places a heavy burden on the kidneys, making it difficult to eliminate waste products. A high-protein diet may cause or exacerbate existing kidney problems. In addition, studies show many health benefits to moving away from an animal-based diet towards one based on plants. Colorful plant foods are nutritional powerhouses and can prevent chronic disease.

• Caffeine: Caffeine found in coffee, tea, soda, and foods can also place a strain on the kidneys. Caffeine is a stimulant, which can cause increased blood flow, blood pressure and stress on the kidneys. Excessive caffeine intake has also been linked to kidney stones.

• Genetically Modified Organisms (GMOs): A large percentage of processed foods contain genetically modified organisms. Unfortunately, the long-term health effects of GMO crops on humans remain unknown due to the lack of studies. However, studies on animals indicate that serious health effects are linked to GMOs. These include changes in major organs like the kidneys.

Challenges and Limitations of GFR

While GFR is a valuable tool in assessing kidney function, it is not without limitations. Factors such as variations in muscle mass, diet, and certain medical conditions can affect serum creatinine levels, leading to potential inaccuracies in GFR estimates. Additionally, GFR may not fully capture all aspects of kidney function, and complementary tests may be required for a comprehensive evaluation.

Diagnosing and managing kidney disorders

In conclusion, Glomerular Filtration Rate (GFR) is a critical parameter in assessing kidney function, providing valuable insights into the efficiency of the kidneys in filtering blood and removing waste products. Understanding the definition, measurement methods, influencing factors, and significance of GFR is essential for healthcare professionals in diagnosing and managing kidney disorders. As research continues to advance, ongoing efforts to refine GFR estimation methods and explore additional biomarkers will contribute to improved accuracy in evaluating kidney health.