Why Are Kidney Function Tests Essential for Health?
The primary function of the kidney is balancing homeostasis. The kidney manages fluid levels, electrolyte balance and others which keep the internal environment of our body stable. The kidney excretes water-soluble wastes from our body. It removes two significant compounds Urea and Uric Acid, which help to purify our blood. The kidney also reabsorbs essential nutrients from the blood and sends them as per need. The reabsorbed products are glucose, amino acids, bicarbonate, sodium, phosphate, chloride, magnesium, potassium, ions etc. The kidney maintains the pH level of the human body, which helps proteins and enzymes not to break down. Beside these, the kidney regulates blood pressure and secretes active compounds such that Erythropoietin, Renin, Calcitriol.
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What Is KFT Test?
KFT test full form is a kidney function test. KFT test means the determination of renal disorders. KFT test is a test to check kidney function. Kidney function test includes urine examination, serum urea, blood urea nitrogen (BUN), calcium, serum creatinine, dilution test.
How To Test Kidney Function?
After collecting the blood sample, we have to compare the urea, creatinine, calcium, nitrogen level with the kidney function to test typical values. Beside this imaging tests can also help. Kidney renal function test is done by the following steps.
Urine Examination – In this process, a physical examination is done, which records the colour, odour, quantity, specific gravity of the urine. A microscopic exam of urine is done to determine any element which should not be present in urine.
Serum Urea – Urea is formed as an end product of protein catabolism. By urea cycle, it is produced from the amino group of the amino acids in the liver. Urea is filtered at the glomerulus, and it is secreted and reabsorbed at the tubular phase. Urea level increases only for the reduction of glomerulus function by 50%. The rise of serum urea level is considered as glomerular dysfunction, which causes renal dysfunction. The standard serum urea value is 20-45 mg/dL. But this value can also be affected by a high protein diet and other non-renal disorders, hepatic injuries. So, determination of serum urea level is not a good detector of kidney disorders. Still, it is one of the most suggested tests for renal dysfunction.
Blood Urea Nitrogen (BUN) – BUN can be determined from serum urea level. By calculating the molecular weight and the contribution of nitrogen in serum urea, we can get the blood nitrogen level. Increase in blood nitrogen level detects Azotemia.
Calcium – By this test, we measure the amount of calcium in blood cells. Usually, calcium is for building and fixing of bones and teeth. It also helps nerves to work and makes the construction of muscles. Calcium helps every body’s cells to work correctly. High calcium level causes headaches, nausea, sore eyes, itchy skin, aching tooth etc.
Serum Creatinine Level – Creatinine is a tripeptide of muscles. Unlike urea, it is a marker of renal function. The problem of glomerular filtration can cause high serum creatinine level. Serum creatinine level can determine glomerular dysfunction. Creatinine level depends on muscle mass and muscle wear. It is a vital part of the kidney function test.
Dilution Test – Dilution test measures the working of tubules. For less reabsorption of tubules, urine becomes diluted. In this test, the patient fasts overnight, and in the morning, drinks 1200 ml of water over 30 minutes. Then urine samples are collected every 4 hours. Urine’s specific gravity of 1.033 or more than that indicates tubular dysfunction.
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Solved Examples
A 53 years old woman is selected for a kidney function test. She didn’t take anything before the test but drank water. A patient would fast for 8-12 hours before the KFT Test.
Now we get From the Kidney Function Test –
Calcium- 11.3 mg/dL, Creatinine- 1.7 mg/dL, Potassium- 6.1 mEq/L, Sodium- 153 mEq/L, Uric Acid- 6.8 mg/dL, BUN- 22 mg/dL.
From the result, the symptoms we get are high blood pressure, blood in urine, frequent urges to urinate, difficulty in beginning urination, painful urination. These symptoms indicate that the kidneys aren’t working correctly. The patient should take treatment accordingly.
Did You Know?
As a result of kidney disease, the risk factors are diabetes, high blood pressure etc. If kidney disease gets worse, it may lead us to kidney failure. It can also cause heart problems, blood vessel disease and many other health problems. People who have these risk factors should check-up regularly. Simple ways to protect our kidneys keep blood sugar, blood pressure, cholesterol under control, eat healthily, do exercise, don’t smoke, and limit alcohol.
FAQs on Kidney Function Test: Types, Methods & Importance
1. What are the primary components of a Kidney Function Test (KFT)?
A Kidney Function Test, also known as a Renal Function Test (RFT), typically measures several key substances in the blood and urine to assess how well the kidneys are working. The main components include:
- Serum Creatinine: Measures the level of creatinine, a waste product from muscle metabolism. Healthy kidneys filter this out, so high levels can indicate poor function.
- Blood Urea Nitrogen (BUN): Measures the amount of nitrogen in the blood that comes from the waste product urea. High BUN levels can suggest kidney issues.
- Glomerular Filtration Rate (GFR): This is a calculation based on your serum creatinine level, age, and gender. It is considered the best indicator of overall kidney function.
- Urine Albumin-to-Creatinine Ratio (UACR): A urine test that checks for albumin, a protein that can pass into the urine when kidneys are damaged.
2. What are the common symptoms that might indicate a need for a kidney function test?
Many early-stage kidney problems have no symptoms. However, as the condition progresses, a doctor might recommend a KFT if you experience any of the following:
- Changes in Urination: Such as urinating more frequently (especially at night), foamy or bubbly urine, or blood in the urine (hematuria).
- Swelling (Edema): Persistent puffiness around the eyes or swelling in the hands, feet, or ankles due to fluid retention.
- Persistent Fatigue: A constant feeling of tiredness or lack of energy, as kidneys help produce red blood cells and filter waste.
- High Blood Pressure: Uncontrolled or newly developed hypertension can be both a cause and a symptom of kidney damage.
- Poor Appetite and Nausea: A buildup of waste products in the blood can lead to a loss of appetite and feeling sick.
3. What are considered normal ranges for key parameters in a Kidney Function Test?
Normal ranges can vary slightly between laboratories, but general reference values are as follows:
- Serum Creatinine: Typically 0.6 to 1.2 mg/dL for men and 0.5 to 1.1 mg/dL for women.
- Blood Urea Nitrogen (BUN): Generally between 7 and 20 mg/dL.
- Glomerular Filtration Rate (GFR): A normal GFR is typically above 90 mL/min. A GFR consistently below 60 mL/min suggests kidney disease.
It is important to have a doctor interpret these results, as factors like age, sex, and muscle mass can affect the values.
4. Why is the Glomerular Filtration Rate (GFR) a more crucial measurement than just serum creatinine alone?
While serum creatinine is a vital part of a KFT, the Glomerular Filtration Rate (GFR) is considered a more accurate and comprehensive indicator of kidney health. This is because creatinine levels can be influenced by factors like muscle mass, age, and diet. GFR, on the other hand, is a calculated measurement that estimates how much blood passes through the glomeruli (the tiny filters in the kidneys) each minute. It directly assesses the kidneys' primary filtering capacity, providing a clearer picture of function and staging the level of kidney damage, which is a concept central to understanding renal physiology as per the NCERT syllabus for 2025-26.
5. How are the results of a Kidney Function Test interpreted to diagnose a problem?
A doctor interprets KFT results by looking at the combination of values, not just one single number. For example:
- Elevated Creatinine and BUN with a low GFR strongly indicates that the kidneys are not filtering waste effectively from the blood. This is a classic sign of kidney impairment.
- Protein (Albumin) in the urine suggests that the kidney's filters (glomeruli) are damaged, allowing large molecules like protein to leak through, which should not happen in healthy kidneys.
- Abnormal Electrolyte Levels (like potassium or sodium) can also point to a problem, as the kidneys play a critical role in balancing these minerals in the body.
The pattern of these results helps a doctor determine the extent and potential cause of the kidney issue.
6. What is the fundamental difference between a Renal Function Test (RFT) and a Liver Function Test (LFT)?
The fundamental difference lies in the organs and functions they assess. A Renal Function Test (RFT/KFT) evaluates how well the kidneys are performing their primary jobs of filtering waste products like creatinine and urea from the blood and balancing fluids. In contrast, a Liver Function Test (LFT) measures levels of specific enzymes (like ALT and AST) and proteins (like bilirubin and albumin) produced or processed by the liver. An LFT is designed to check for liver damage or inflammation, not renal filtration capacity.
