IMPORTANCE OF RENAL/KIDNEY FUNCTION TEST(RFT)

Kidneys are important organs in the body. It is important to see that their work is going on smoothly, so if any symptoms appear in the future, it would be beneficial to consult a doctor immediately.Renal function tests are used to evaluate kidney function. Kidneys play an important role in removing waste products from the body, as well as regulating electrolyte balance, blood pressure, and acid-base balance.

.ABOUT KIDNEYS:-

Location in the body:-

·        Kidneys are a pair of bean-shaped organs located in the abdominal cavity on either side of the spine, just under the ribcage.

·        They are retroperitoneal organs, which means they are situated behind the peritoneum (the lining of the abdominal cavity) and are not covered by it.

·        The kidneys are situated between the adrenal gland and the ureter. The top part of each kidney is located just below the diaphragm, while the bottom part extends into the pelvis

 

Size:-

·       The right kidney is slightly lower than the left due to the position of the liver. Each kidney is about 4-5 inches in length and 2-3 inches in width, and weighs around....

Left kidney ----- Male--------	117.9 ± 27.4 g    Female --------			108.3 ± 23.0 g
Right kidney ---- Male--------	110.0 ± 22.8 g    Female --------			101.2 ± 20.3 g

 

                                                                           

Functions :-

·       The extracellular fluid constitutes the internal environment of the cells of the body.The cells carry out their vital activities in this medium. This fluid should be maintained relatively constant in composition for the normal functioning of the cells since changes in extracellular fluid are reflected in changes in the fluid within the cells (intracellular fluid) and also in the cell functions.

·      This internal environment is regulated mainly by two pairs of organs 

     (1) The lungs : These control the concentration  of oxygen and CO2.

2) The Kidneys: These maintain optimal chemical composition of the body fluids by acidification of urine and also by removing metabolic wastes such as urea, creatinine, uric acid and ions such as ammonium and sulfates. 

·        The regulation of the internal environment by kidneys is a composite of four processes 

(1) Filtration of blood plasma by glomeruli. Approximately liter of blood flows through kidneys per minute by maintaining average glomerular filtration rate 125 ml/ minute. The filtrate is free from blood cells and proteins. 

(2) Selective re-absorption by tubules of materials required in maintaining internal-environment. High threshold substances such as glucose, fatty acids, amino acids and bicarbonate are completely reabsorbed while sodium, potassium, calcium, in-organic phosphorus and other ions are reabsorbed in a controlled manner. 

(3) Secretion by the tubules of certain substances such as creatinine and potassium 

(4) Exchange of hydrogen ions and ammonia for the conservation of bicarbonate...

·      The kidneys receive blood from the renal arteries and filter it to remove waste products, excess water, and electrolytes, which are then excreted out of the body through urine.

·      The ureters connect the kidneys to the bladder, which stores urine until it is expelled from the body through the urethra. Overall, the kidneys play a crucial role in maintaining homeostasis by regulating the balance of important substances in the body.

·       The normal kidney functions such as formation, acidification, concentration or dilution of urine,along with filtration of blood at glomeruli and selective re-absorption of essential substances, con- trolled re-absorption of salts and water, secretion of certain substances depend upon an adequate blood flow to the kidneys.

 

Symptoms of kidney disease

Symptoms are depending on the stage and underlying cause of the disease. Some common symptoms include:

·        Fatigue

·        Swelling in the hands, feet, or face

·        Loss of appetite

·         Nausea and vomiting

·        Itching and dry skin

·         Urinating more or less than usual

·         Difficulty in sleeping

·         Short breath or difficulty breathing

·         High blood pressure

·         Muscle cramps or weakness

·        Blood in urine

·        Decreased mental sharpness

·         Metallic taste in the mouth

·         Bone pain or fractures

·        Increased vulnerability to infections

·         Inability to concentrate or think clearly

·        Decreased urine output

·        Abdominal pain and discomfort

·        Swelling or fluid buildup in the lungs.

It is important to seek medical attention if any of these symptoms are experienced as early diagnosis and treatment can help slow the progression of kidney disease.

 

IN RENAL DISEASE...

• In renal disease, due to the disturbance in the above mentioned four processes and mainly due to decreased glomerular filtration rate. 
• waste products particularly nitrogenous substances such as urea, creatinine and uric acid tend to increase in blood.
• Any situation that interferes with renal blood supply will result in diminished kidney function and will alter the amount and composition of urine. 
• With the result, accumulation of metabolic waste products will take place in blood. Patients in cardiac failure (pre-renal condition) frequently have diminished kidney function due to an inadequate flow of blood to the kidneys although the kidneys are normal in condition.

 

The list of Renal Function Tests (RFT) includes:

1. Blood Urea Nitrogen (BUN) test

2. Creatinine blood test

3. Blood electrolyte tests (sodium, potassium, chloride, bicarbonate)

4. Serum calcium  tests

5. Serum uric acid test

7. Serum alkaline phosphatase.

8. Serum Protein Test

9. Bicarbonates

10. Magnesium

11. Phosphorus

12. Urine Routine Test

These tests are used to evaluate the function of the kidneys, to diagnose kidney diseases and disorders, and to monitor the effectiveness of the treatment. Some of these tests require blood and urine samples. Your doctor will determine which tests to perform based on your medical history, symptoms and physical examination.

 

Following is some special information about renal function tests:-

1. Types of Renal Function Tests:

·        Blood tests (such as creatinine, blood urea nitrogen, uric acid)

·        Urine tests (such as 24-hour urine protein and urine Routine)

·        Sometimes Imaging tests (such as ultrasound and CT scan).

 

Kidney function tests can be separated into the following groups:-

Group I Tests:-

1) Blood urea nitrogen.

2) Serum creatinine

3) Routine urine examination

Explaination:-  

• These tests can be helpful to differentiate pre-renal condition from renal and post renal conditions. 
• Simultaneous urea nitrogen and creatinine determinations appear to have some clinical significance. Normal ratio of urea nitrogen and serum creatinine is observed to be 14 to 24.
•  In cases of retention of urea nitrogen due to pre-renal causes the ratio is generally observed to be higher and may be up-to 40.
•  In the absence of pre-renal conditions, however, during the early stages of renal disease the ratio, urea nitrogen/creatinine may be normal since the tubules can secrete raised serum creatinine up to a level.
•  In the presence of normal renal blood flow, any increase in creatinine values above 2 mg/dl is suggestive of moderate to severe kidney damage and in severe tubular damage the ratio may be as low as 10.
•  Retention of urea and creatinine due to obstruction of the urinary tract in post renal conditions will cause simultaneous and proportional increase in both serum urea nitrogen and creatinine levels. The ratio will be below 14, depending upon the percentage of obstruction to urea excretion.
•  Examination of urine for protein, cells and casts give idea of an 'active lesion'.
•  Once the renal damage has been detected, renal function tests may reveal the principal site and degree of the disturbance in nephron.

 

In the case of a renal disease, to assess the severity of the disease, the following, additional tests may be performed.

 Group II Tests:-

1) Serum total protein, albumin, globulin and A/G ratio,

2) Quantitative determination of urinary proteins.

3) Electrophoretic fractionation of serum proteins.

4) Serum cholesterol.

• In nephritis type I(Glomerulonephritis):-In this moderate loss of proteinuria is observed.
• In nephritis type II (nephrotic syndrome):-In this massive loss of proteinuria is observed. A typical  protein pattern with decreased albumin and gamma globulin but increased beta and alpha 2-globulin indicates nephritis. 
• In nephritis II:-In this moderate increase in serum cholesterol is observed while very high values  are  observed in nephritis II.               

           

 Group III tests:-

 Tests measuring glomerular filtration.

1) Creatinine clearance test.

2) Urea clearance tests.

Explaination:- 

1) Creatinine clearance test.

• These tests measure the actual excretory capacity of the kidney since they measure the amount of a substance excreted in the urine as compared to the concentration of the same substance in the plasma. 
• Clearance tests are considerably more sensitive and clinically more useful than the tests measuring retention of substances such as urea and creatinine; since these substances may not elevate in blood until there is a significant decrease in kidney function (below 50% of normal clearance)
• At normal levels of creatinine in the blood, it is filtered at the glomerulus but neither secreted nor re-absorbed by the tubule. Hence in that case, creatinine clearance may also give the glomerular filtration rate (GFR) which is 120 ml per 1.73 sq. m. body surface area.

•  Normal values for creatinine clearance :-

          105+20 ml/min. for Males

          95± 20 ml/min. for Females.

• Creatinine clearance values less than 50 ml are of graver prognostic significance.

       2)  Urea clearance tests:-

• Urea clearance values less than 50% of normal average indicate renal failure and urea clearance falls below 20% in severe renal failure.

 

Group IV tests:-

Tests measuring tubular function.

1) Determination of specific gravity, concentrating and  diluting ability of kidneys.

2) Determination of serum and urine osmolarity.

3) Determination of urine ammonia.

4) Phenolsulfonaphthalein (PSP) test.

Explaination:-

1) The simple specific gravity tests designed to determine concentrating power and dilution power of kidneys can be useful to indicate presence of renal defect in some cases where the blood urea is within normal limits.

2) Osmolarity is a measure of the total concentration of dissolved particles in the specimen. The concentrating activity of the renal tubules is regulated by 'osmoreceptors' which are sensitive to changes in the solute concentration rather than to changes in the specific gravity. The normal ratio of urine osmolarity to serum osmolarity is 3.0 or more. Thus these determinations give better idea of concentrating ability of the tubules.

3) Determination of ammonia in urine gives measure of the ability of the tubules to produce ammonia in state of acidosis.

4) Phenolsulfonaphthalein (PSP) is a dye that is removed from plasma to about 60 to 70% during one passage through the kidneys. About 20% is normally removed by the liver. Of that portion of the dye that is removed by the kidneys, about 6% is excreted by glomerular filtration and about 94% by tubular excretion. The test mainly gives measure of the secretory capacity of the tubules.In the absence of renal disease,the test may be used as a measure of renal blood flow. 

  

Note: In the normal individuals 25% or more of the dye will be excreted during the first 15 minutes after intravenous injection and no less than 70% will be excreted during the two hour period. The rate at which the dye appears in the urine depends upon the action of tubular epithelial as well as the renal blood flow.

 

 Group V tests:-

 Tests determining acid-base status:-

1) Serum electrolytes (sodium, potassium and chlorides)      

2) Serum inorganic phosphorus and calcium.

3) Serum bicarbonate.

4) Blood gases (PO,, PCO2) and blood pH.

Explaination:- 

•  Metabolic acidosis is a characteristic complication of renal disease. It is caused by accumulation of phosphates, sulfates and non protein nitrogenous substances in blood.

• There may be a failure of the renal tubular mechanism for secretion of hydrogen ions and for the formation of ammonia. Depletion in se- rum bicarbonate (alkali reserve) may take place.

• Acidic anions such as phosphates and sulfates are buffered by cations which cannot be recaptured and returned to blood in exchange for hydrogen ions by the tubules.

• Re-absorption of sodium is defective, which causes hypokalemia and severe dehydration may occur, secondary to the electrolytic depletion.

• Potassium can be excreted by tubular secretion as well as by filtration hence in chronic renal failure serum potassium may be normal or slightly elevated

 

2. Interpretation of Results (Reporting):-

·  Interpretation of renal function test results depends on which tests are performed.

·  However, in general, if kidney function becomes irregular, it indicates kidney failure, which can be caused by insufficient water intake, drug use, or underlying medical conditions such as diabetes or nephritis.

·  With early blood tests and proper management, kidney function can often be improved.

3. Importance of monitoring Renal Function:

• Renal function should be monitored regularly, especially in patients with chronic kidney disease or other conditions affecting the kidneys. 

• Early detection of kidney dysfunction can prevent further damage and help to improve kidney function.

 

4. Potential Limitations of Renal Function Tests:-

·   Although Renal function tests are useful tools for assessing kidney function, they have some limitations.

·   For example, some tests may not detect the early stages of kidney failure, and factors such as the patient's hydration status and medications may lead to inaccurate reports.

 

5. Patient Preparation for Renal Function Test:

• Patients have to follow certain preparations before undergoing renal function tests.  
• For example, they may be asked to avoid certain medications, preferably fast for a certain period of time, or take a 24-hour/ Morning first urine sample. 
• Patients should follow their healthcare provider's instructions carefully to ensure accurate and reliable test reports

 6. Sample for testing :-

• Blood  Serum sample from Plain tube.

Methods to keep your kidney healthy:-

1.Stay hydrated: 

• Drinking enough water helps your kidneys function properly. It is necessary to drink at least 8-10 glasses of water every day.

2. Reduce salt intake: 

• High salt intake can damage the kidneys and increase the risk of high blood pressure. Try to reduce your intake of processed foods and limit your salt intake.

3. Maintain a healthy diet: 

• Eating a balanced diet that includes fresh fruits, vegetables, whole grains and protein can help keep the kidneys healthy. Avoiding too much protein or fat can also help.

4. Exercise regularly: 

• Regular physical activity can improve blood circulation and help balance kidney function. Aim for at least 30 minutes of exercise every day.

5. Avoid smoking and heavy drinking: 

• Smoking and heavy drinking can damage the kidneys and lead to various health complications. Quit smoking and limit alcohol consumption.

6. Manage blood sugar and blood pressure levels: 

• High blood sugar and blood pressure can damage the kidneys over time. Kidney health can be maintained if they are controlled with medication and lifestyle changes.

7. Get regular kidney function tests: 

• Regular tests can help detect any potential kidney problems early, leading to early diagnosis and treatment. Discuss with your doctor when to have kidney function tests.

Reference-9.Chemical test in Kidney disease.Textbook of Medical Laboratory Technology,Dr.Prafulla Godkar