A 101 Guide to Kidney Function Tests: Types, Results & Follow-Up Recommendations

Your kidneys work nonstop, filtering waste products and keeping the body’s blood chemistry in check. But how do you know if they're functioning optimally? That’s where kidney function tests (KFT tests) come in, offering a window into your kidney health, potentially detecting various kidney-related disorders, guiding treatment decisions, and monitoring the progression of any renal conditions. In this comprehensive guide, we'll shed light on the different types of tests, what they measure, and how the results are interpreted by healthcare professionals. Read on to become an active participant in your own health, allowing you to take steps to maintain optimal kidney function for years to come.

What are Kidney Function Tests?

Kidney function tests are a series of medical exams that check kidney function. These tests can be blood tests, urine tests, or sometimes a combination of both. They are important because your kidneys play a vital role in filtering waste products and excess fluid from your blood, keeping your blood pressure stable, and producing hormones that are essential for overall health.

Here's a breakdown of what kidney function tests do:

• Measure waste products in your blood: Healthy kidneys filter out waste products. If these levels are elevated in your blood, it could be a sign that your kidneys aren't working as well as they should.
• Check for abnormalities in your urine: Your urine normally shouldn't contain high levels of protein or blood cells. The presence of these can indicate kidney problems.
• Estimate your glomerular filtration rate (GFR): GFR is a measure of how efficiently your kidneys filter waste products from your blood. There are different ways to estimate GFR, often using blood tests.

Types of Kidney Function Tests

Kidney function tests can primarily be divided into three main types- i.e., blood tests, urine tests and imaging tests. These tests provide an overview of the kidney’s functioning ability. Let's have a closer look at each of the kidney function test types and their subtypes:

Blood tests

Blood tests for kidney function measure the levels of waste products in your blood that are normally removed by your kidneys. Examples of these waste products include creatinine and blood urea nitrogen (BUN).

Blood Urea Nitrogen (BUN) Test 

This test measures the amount of nitrogen in your blood that comes from the waste product urea. Urea is produced when the liver breaks down proteins, and it is normally excreted by the kidneys. Elevated levels of BUN can indicate kidney dysfunction or other conditions affecting kidney function.

Serum Creatinine Test

Creatinine is a waste product produced by muscles. This test measures the level of creatinine in the blood. Elevated kidney creatinine levels can suggest impaired kidney function because healthy kidneys filter creatinine from the blood and excrete it in the urine.

Estimated GFR (eGFR) Calculation

eGFR test for kidney function is a calculation based on serum creatinine levels, age, gender, and race. It estimates how much blood passes through the glomeruli, the tiny filters in the kidneys, each minute. eGFR is considered one of the best indicators of kidney function. A lower eGFR value indicates decreased kidney function.

Urine tests

Urine tests check for abnormalities in your urine, such as the presence of protein or blood, another indication of kidney malfunction or disease.

Microalbuminuria

Microalbuminuria is the presence of small amounts of a protein called albumin in the urine. This test measures the level of albumin in the urine, which can indicate early kidney damage. Healthy kidneys filter waste products, including proteins, from the blood into the urine. However, when the kidneys are damaged, they may allow small amounts of protein, such as albumin, to leak into the urine. Microalbuminuria testing is crucial for detecting kidney damage in its early stages, particularly in individuals at risk of kidney disease, such as those with diabetes or hypertension.

Urinalysis

Urinalysis is a broad screening test that examines the physical and chemical properties of urine. It assesses various components of urine, including colour, clarity, pH, specific gravity, and the presence of substances such as glucose, ketones, blood cells, and bacteria. Urinalysis can provide valuable information about kidney function, urinary tract infections, kidney stones, and other renal conditions. It is often one of the first tests performed to evaluate kidney health and urinary system function.

Proteinuria Test

Proteinuria is the presence of excess protein in the urine. This test measures the amount of protein excreted in the urine over a specified period, typically 24 hours. Proteinuria can be an early sign of kidney disease or other conditions affecting the kidneys' ability to filter waste products from the blood. It is essential for monitoring kidney function and assessing the severity of kidney damage. Elevated levels of protein in the urine may indicate glomerular damage, tubular disorders, or systemic conditions such as diabetes or hypertension.

Imaging tests

Ultrasound or X-ray, can be used to create images of your kidneys. Imaging tests can help your doctor assess the size and shape of your kidneys and identify any blockages or abnormalities. 

Ultrasound Scan

An ultrasound scan, also known as renal ultrasound or renal sonogram, uses sound waves to create images of the kidneys and urinary tract. It can help visualise the size, shape, and structure of the kidneys, as well as detect abnormalities such as kidney stones, cysts, tumours, and obstruction in the urinary tract. It is a non-invasive and painless imaging technique commonly used to evaluate kidney health and diagnose various renal conditions.

CT Scan 

A CT scan uses X-rays and computer technology to create detailed cross-sectional images of the kidneys and surrounding structures. It provides more detailed images than ultrasound and can detect smaller abnormalities with greater accuracy. CT scans are valuable for diagnosing kidney stones, tumours, cysts, infections, and other renal conditions. 

MRI Scan

MRI uses a powerful magnetic field and radio waves to generate detailed images of the kidneys and surrounding tissues. MRI provides excellent soft tissue contrast and can detect abnormalities such as tumours, cysts, and vascular disorders in the kidneys. It is particularly useful for evaluating complex renal conditions and assessing kidney function without the need for contrast dye.

Other tests and measures for kidney function

• Electrolyte Panel Test: An electrolyte panel test measures the levels of electrolytes such as sodium, potassium, chloride, and bicarbonate in the blood. Electrolytes play crucial roles in maintaining fluid balance, nerve function, and muscle contraction, among other physiological processes. Imbalances in electrolyte levels can occur due to kidney dysfunction, dehydration, certain medications, or other medical conditions. Monitoring electrolyte levels helps assess kidney function and guide treatment for electrolyte imbalances, which are common in kidney disease.
• Albumin-to-Creatinine Ratio (ACR): The albumin-to-creatinine ratio (ACR) is a urine test that measures the ratio of albumin (a protein) to creatinine (a waste product) in the urine. ACR is used to detect and quantify the amount of albuminuria, or excess albumin in the urine, which is an early sign of kidney damage. Elevated ACR levels indicate increased permeability of the kidney's filtration barrier, allowing albumin to leak into the urine. ACR testing is essential for diagnosing and monitoring kidney disease, particularly in individuals with diabetes or hypertension, who are at increased risk of developing kidney damage.
• Cystatin C Test: Cystatin C is a protein produced by cells throughout the body at a constant rate and is freely filtered by the kidneys. The cystatin C test measures the level of cystatin C in the blood, which serves as a marker of kidney function. Unlike creatinine, cystatin C levels are less influenced by factors such as age, muscle mass, or diet. Therefore, cystatin C testing may provide a more accurate estimation of glomerular filtration rate (GFR) and kidney function, particularly in individuals with fluctuating muscle mass or those with conditions affecting creatinine metabolism. 

Interpretation of Test Results

Interpreting kidney function test results involves analysing various parameters measured in blood and urine tests to assess the health and functionality of the kidneys. Abnormal results may prompt further evaluation, monitoring, or treatment by healthcare professionals to manage kidney disease and associated complications effectively.

Normal Ranges for Kidney Function Tests 

Kidney function test normal range varies depending on the specific test performed and the laboratory's reference values. Generally, normal ranges for common renal function tests include:

• Blood Urea Nitrogen (BUN): 7 to 20 mg/dL
• Serum Creatinine: 0.6 to 1.2 mg/dL for men and 0.5 to 1.1 mg/dL for women
• Estimated Glomerular Filtration Rate (eGFR): Above 90 mL/min/1.73m² is considered normal values of GFR.
• Urine Albumin-to-Creatinine Ratio (ACR): Less than 30 mg/g is considered normal

Explanation of Abnormal Results and What They May Indicate

Abnormal kidney function test results may indicate underlying renal dysfunction or other medical conditions affecting kidney health. Common abnormalities and their potential implications include:

• Elevated BUN and creatinine levels: May indicate decreased kidney function, dehydration, urinary tract obstruction, or other renal conditions.
• Decreased eGFR: Indicates reduced kidney function and may be indicative of chronic kidney disease (CKD) or acute kidney injury (AKI).
• Elevated ACR levels: Suggest increased permeability of the kidney's filtration barrier, which may indicate kidney damage or microalbuminuria, often seen in diabetes or hypertension.
• Abnormal electrolyte levels: Imbalances in electrolytes such as sodium, potassium, chloride, or bicarbonate may result from kidney dysfunction, dehydration, or other medical conditions.

Follow-Up Recommendations

The next step is understanding the follow-up recommendations tailored to your specific results. These recommendations will guide your path forward, whether your tests fall within the normal range, indicate potential issues, or suggest existing kidney disease.

Actions to take after receiving abnormal test results

Receiving abnormal renal function test (RFT tests) results can be concerning, but taking prompt action is essential for managing kidney health effectively. Here are some steps to consider:

• Schedule a follow-up: If your test results show anything out of the ordinary, it's important to connect with your doctor as soon as possible. Schedule a follow-up appointment to discuss the details. Don't hesitate to bring any questions or concerns you may have.
• Understand your results: Understanding your test results is key. Take some time after your appointment to really absorb the information. Don't be afraid to ask your doctor to explain things again in simpler terms if needed. 
• Follow doctor’s guidance: Your doctor will likely recommend some next steps, whether it's additional testing, specific treatments like kidney failure treatment (if diagnosed), or lifestyle changes. Following their plan is crucial for better kidney health.

Lifestyle changes to improve kidney health

Making healthy lifestyle changes is essential for promoting kidney health and reducing the risk of kidney disease progression. Here are some lifestyle modifications to consider:

• Diet modifications: Making dietary changes can significantly impact kidney health. Reducing sodium intake is crucial as it helps manage blood pressure and decreases strain on the kidneys. Monitoring protein intake is equally important, especially for individuals with kidney disease, as excessive protein consumption can strain the kidneys. 
• Exercise recommendations: Regular physical activity plays a vital role in promoting kidney health. Engaging in at least 30 minutes of moderate-intensity exercise most days of the week supports cardiovascular health and helps maintain a healthy weight. 
• Medication adjustments: Following medication instructions and monitoring for potential side effects are crucial aspects of managing kidney health. Taking prescribed medications as directed by your healthcare provider helps manage underlying conditions such as high blood pressure or diabetes, which can affect kidney function.

Conclusion

Kidney function tests are invaluable tools for assessing and maintaining your kidney as well as overall health. By providing insights into kidney function, these tests enable early detection and management of renal conditions, ultimately safeguarding against potential complications. If kidney health concerns arise, Max Hospitals stands ready with experienced nephrologists to answer your questions and manage a wide range of kidney conditions. Prioritise your kidney health. Book a consultation with a specialist at Max Hospitals today.