Renal Function Test (RFT)

Original Editor - Manisha Shrestha Top Contributors - Manisha Shrestha, Lucinda hampton and Joao Costa

Introduction

Renal function tests (RFT) are a group of tests that may be performed together to evaluate kidney (renal) function. The tests measure levels of various substances, including several minerals, electrolytes, proteins, and glucose (sugar), in the blood to determine the current health of the kidneys.

If the kidneys are not functioning properly, waste products can accumulate in the blood and fluid levels can increase to dangerous volumes, causing damage to the body or a potentially life-threatening situation. Numerous conditions and diseases can result in damage to the kidneys. The most common causes of and main risk factors for kidney disease are diabetes and hypertension.

Indication

Indications for the assessment of renal function are varied and range from acute emergency to chronic settings.

1. Primarily, renal function tests are performed to identify the renal disease to determine appropriate patient management and prevent further deterioration of renal function.
2. Further indications in patients in whom the renal disease has been identified are to stage level or type of renal disease and to monitor the progression of renal disease to ensure that optimal management occurs and to monitor response to interventions.

Components of RFT

RFT, a group of tests that may be performed together, evaluate kidney (renal) function. The tests measure levels of various substances, including several minerals, electrolytes, proteins, and glucose (sugar), in the blood to determine the current health of the kidneys.

Clinically, the most practical tests to assess renal function is to get an estimate of the glomerular filtration rate (GFR) and to check for proteinuria (albuminuria).

Test to assess the kidney function

It is very essential to know the function of kidney and also the process of urine formation to know the rational behind these test and also to interpret the result of these test.

Glomerular Function- Clearance test

Within the kidneys are about a million tiny blood filtering units called nephrons. In each nephron, blood is continually filtered through a cluster of looping blood vessels, called a glomerulus, which allows the passage of water and small molecules but retains blood cells, proteins such as albumin, and larger molecules.

The best test to assess glomerular function is Glomerular filtration rate (GFR), which is the rate in milliliters per minute at which substances in plasma are filtered through the glomerulus; in other words, the clearance of a substance from the blood. The normal GFR for an adult male is 90 to 120 mL per minute.

Testing for GFR can be a complicated and lengthy procedure, which is why doctors use a formula to estimate GFR or eGFR. The standard way to estimate GFR is with a simple blood test that measures creatinine levels. Creatinine is a waste product from the digestion of dietary protein and the normal breakdown of muscle tissue. Aside from chronic kidney disease, creatinine levels can be affected by other factors, including diet, muscle mass, malnutrition, and other chronic illnesses.

According to the Kidney Disease Improving Global Outcomes (KDIGO), The stages of chronic kidney disease (CKD):

• Stage 1 GFR greater than 90 ml/min/1.73 m²  
• Stage 2 GFR-between 60 to 89 ml/min/1.73 m²
• Stage 3a  GFR 45 to 59 ml/min/1.73 m²
• Stage 3b GFR 30 to 44 ml/min/1.73 m²
• Stage 4 GFR of 15 to 29 ml/min/1.73 m²
• Stage 5-GFR less than 15 ml/min/1.73 m² (end-stage renal disease)

Typical Tests Performed

The individual tests included in a kidney function panel can vary by laboratory, but the tests typically performed include:

1. Electrolytes – electrically charged chemicals that are vital to normal body processes, such as nerve and muscle function; among other things, they help regulate the amount of fluid in the body and maintain the acid-base balance. Electrolytes include:

• Sodium
• Potassium
• Chloride
• Bicarbonate (Total CO2)

2. Minerals

• Phosphorus – a mineral that is vital for energy production, muscle and nerve function, and bone growth; it also plays an important role as a buffer, helping to maintain the body's acid-base balance.
• Calcium – one of the most important minerals in the body; it essential for the proper functioning of muscles, nerves, and the heart and is required in blood clotting and in the formation of bones.

3. Protein

• Albumin – a protein that makes up about 60% of protein in the blood and has many roles such as keeping fluid from leaking out of blood vessels and transporting hormones, vitamins, drugs, and ions like calcium throughout the body.

4. Waste products

• Urea – urea is a nitrogen-containing waste product that forms from the metabolism of protein; it is released by the liver into the blood and is carried to the kidneys, where it is filtered out of the blood and eliminated in the urine.
• Creatinine – another waste product that is produced by the body's muscles; almost all creatinine is eliminated by the kidneys.

5. Energy Source

• Glucose – supplies energy for the body; a steady amount must be available for use, and a relatively constant level of glucose must be maintained in the blood.

Clinical Significance

• Creatinine: Serum creatinine is elevated when there is a significant reduction in the glomerular filtration rate or when urine elimination is obstructed.  About 50%  of kidney function must be lost before a rise in serum creatinine can be detected. Thus serum creatinine is a late marker of acute kidney injury.
• BUN : Serum urea/BUN level increases in acute and chronic renal disease.
• eGFR equations are used to determine the presence of renal disease, stage of CKD, and to monitor response to treatment.

s the Modified Diet in Renal Disease (MDRD) and the CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equation. These eGFR equations are superior to serum creatinine alone since they include race, age, and

Significance

Chronic kidney disease is not only a major risk factor for dialysis but also increases the risk of cardiovascular diseases and is closely related to lifestyle-related diseases such as diabetes and hypertension. In addition, dialysis patients develop complications including cardiovascular diseases, infections, and malignant neoplasms and have a very poor prognosis as the mortality 3 years after the initiation of dialysis exceeds 30%.

Since it is a chronic disease, a multidisciplinary treatment approach and patient centered treatment will be very beneficial. Renal rehabilitation was defined as “a long-term comprehensive program consisting of exercise therapy, diet therapy and water management, drug therapy, education, psychological/mental support, etc., to alleviate physical/mental effects based on kidney disease and dialysis therapy, prolong the life expectancy, and improve psychosocial and occupational circumstances.”