What is Creatinine? How is it different from BUN and eGFR

In an era where people are paying more attention to health, many people therefore place importance on annual health check-ups, and often we may see the term “Creatinine” appearing in blood test reports, which may cause questions about what Creatinine is and how important it is to health. If the test result is abnormal, what should be done

In this article, it will help you understand Creatinine, one of the important indicators of kidney function, including other related values such as BUN and eGFR, so that you can initially read your test results by yourself, along with planning to cope and take care of your health appropriately

Key Takeaways

• Creatinine is a waste substance derived from the breakdown of Creatine in muscles. It is one of the indicators of kidney function efficiency, similar to BUN and eGFR

• A higher-than-normal Creatinine level may indicate decreased kidney function, or a lower-than-normal Creatinine level may indicate other health problems such as low muscle mass, malnutrition, etc.

• An abnormal Creatinine level may not necessarily mean kidney disease; similarly, a normal Creatinine level may still occur while the kidneys are not functioning at full efficiency. Therefore, it is necessary to consider other values such as BUN and eGFR together

Understanding kidney function and its important roles in the body system

The kidneys are internal organs that are important to the human body, playing a major role in excretion and regulation of fluid balance in the body. In addition, the kidneys are also involved in other systems such as the circulatory system, maintaining mineral balance and acid-base balance, as well as producing several types of hormones

Kidney function begins with the circulatory system delivering waste blood to the kidneys. The kidneys then function to filter waste and toxins from the blood and excrete them in the form of urine. In addition to these wastes, the kidneys also excrete excess water and electrolytes, while adjusting acid-base balance so that the body maintains an internal environment suitable for the functioning of various cells. Furthermore, the kidneys also have other roles such as producing certain hormones to stimulate red blood cell production and regulating blood pressure within the normal range

For this reason, the kidneys are organs that play a role in overall health. If the kidneys become abnormal and cannot function efficiently, it may severely affect the body, ranging from hypertension, anemia, edema, to kidney failure, and ultimately death when the kidneys can no longer function

Are the kidneys having problems? It can be known from kidney function tests

How can it be known whether the kidneys are having problems? It can be seen from kidney function test results (Kidney Function Tests), which are methods to assess kidney health and screen for kidney disease by measuring values related to kidney function, including

• Creatinine, BUN, or eGFR, which can be detected from blood

• Albumin, Urinalysis, which can be detected from urine

Screening for kidney disease helps physicians diagnose whether your kidneys can still function well. If abnormalities are detected, appropriate treatment planning can be made, reducing the chance of kidney damage effectively

What is Creatinine?

Creatinine is a waste substance derived from the breakdown of Creatine in muscles. Creatinine circulates in the bloodstream, and the kidneys function to filter Creatinine from the blood and excrete it in the urine. Measuring Creatinine in the blood helps indicate the kidney’s ability to function. If the Creatinine level in the blood is higher than normal, it may indicate decreased kidney function, meaning the kidneys cannot fully filter Creatinine from the blood

However, Creatinine values may vary due to many factors such as sex, age, high muscle mass, high meat consumption, as well as the use of certain medications. Therefore, Creatinine alone cannot be used to determine kidney function; it should be considered together with other values for more accurate diagnosis

Normal Creatinine values differ by sex as follows

• Normal Creatinine in females: 0.5–1.0 mg/dL

• Normal Creatinine in males: 0.7–1.2 mg/dL

What is BUN?

Blood Urea Nitrogen or BUN is the nitrogen component of urea, which is a waste product resulting from protein breakdown in the body. Measuring BUN in the blood helps indicate the kidney’s ability to filter urea nitrogen. If high BUN is detected in the blood, it may be a sign that the kidneys cannot efficiently filter urea nitrogen

BUN values may vary depending on age and sex

• Normal BUN in children: 7–20 mg/dL

• Normal BUN in adult females: 6–21 mg/dL

• Normal BUN in adult males: 8–24 mg/dL

What is eGFR?

Estimated Glomerular Filtration Rate or eGFR is a value estimating the rate at which the kidneys filter waste per minute. This measurement is usually calculated based on the Creatinine level found in the blood. The result is expressed in milliliters per minute per 1.73 square meters (mL/min/1.73 m²), meaning how much waste the kidneys can filter from the blood in 1 minute. A higher eGFR indicates better kidney function; conversely, a low eGFR may indicate that the kidneys cannot efficiently eliminate waste

eGFR gradually decreases with age, even without kidney disease. The following are average values considered within the normal range

• Age 20–39 years: normal eGFR approximately 107–116

• Age 40–59 years: normal eGFR approximately 93–99

• Age 60 years and above: normal eGFR approximately 75–85

If eGFR is below 60, it may indicate decreased kidney function and begin to affect health. If eGFR remains low continuously for more than 3 months, there may be a risk of chronic kidney disease

What causes abnormally high Creatinine?

If blood test results show Creatinine higher than normal, it may indicate accumulation of Creatinine waste in the blood. The causes are as follows

Abnormal kidney function

High Creatinine in the blood may indicate reduced ability of the kidneys to eliminate waste from the blood, which may be caused by conditions or diseases related to the kidneys, including

• Chronic kidney disease: occurs from gradual deterioration of the kidneys, reducing the efficiency of filtering waste from the blood

• Acute kidney failure: a condition in which the kidneys suddenly lose their ability to function

• Nephritis: inflammation of kidney tissue causing swelling and reduced ability to filter waste

• Kidney stones: obstruction prevents full excretion of urine, increasing kidney pressure and causing damage

• Immune-mediated kidney damage: the immune system attacks kidney tissue, causing damage and reduced function

Use of certain medications that affect excretion of Creatinine from the body

Some medications affect kidney function such as NSAIDs, certain antibiotics, or diuretics

Rhabdomyolysis

Rhabdomyolysis is a condition in which muscle cells are rapidly and severely damaged, causing substances within muscles such as Creatine and Myoglobin to be released into the bloodstream in large amounts, including Creatinine which is a byproduct of Creatine breakdown. Increased Myoglobin can directly affect the kidneys, and if not properly treated, may lead to acute kidney failure and may develop into chronic kidney failure in the long term

Dehydration

Dehydration causes the blood to become more concentrated, resulting in higher concentrations of substances dissolved in the blood. In severe dehydration, the kidneys may not be able to filter waste from the blood normally and may eventually lead to kidney failure

Consumption of foods high in Creatine or protein

High blood Creatinine levels may result from consuming foods high in Creatine such as red meat or high-protein supplements. Increased Creatine may lead to greater breakdown into Creatinine than normal, but this is usually temporary and does not affect the kidneys

Heavy exercise, high muscle mass

Individuals with high muscle mass tend to have more Creatinine breakdown than normal. This condition is commonly found in bodybuilders

Effects from certain medications

Some medications do not impair kidney function but interfere with the excretion of Creatine through the kidneys, such as Trimethoprim, Cimetidine, Ritonavir, Fenofibrate, etc.

Complications from other diseases

Many chronic serious diseases may affect the kidneys, including heart disease, diabetes, and hypertension, all of which are factors that can cause rapid kidney deterioration

What should be done if high Creatinine is detected?

High Creatinine may be a warning sign of health problems that should not be ignored. Therefore, if high Creatinine is found, the following recommendations should be followed

• Undergo additional kidney function tests such as measuring BUN and eGFR in blood or Albumin and Urinalysis in urine to more accurately assess overall kidney function

• Reduce consumption of strongly flavored and high-sodium foods to avoid burdening the kidneys in filtering waste

• Avoid use of medications or herbs that may affect the kidneys

• Drink sufficient water to help reduce the concentration of Creatinine in the blood

• Exercise appropriately, not excessively, to prevent rhabdomyolysis and resulting increase in Creatinine

• Control underlying diseases to safe levels, such as controlling blood glucose in diabetic patients and maintaining blood pressure within normal range consistently

In cases where Creatinine is high to the level of stage 5 chronic kidney disease (end stage), dialysis may be required to reduce accumulated waste in the blood, or kidney transplantation may be needed so the body can excrete waste and maintain electrolyte balance again

What causes abnormally low Creatinine?

Conversely, if Creatinine is lower than normal, it indicates that the body may produce less Creatinine from Creatine breakdown, which may occur due to the following causes

Low muscle mass

People with low muscle mass will have less breakdown into Creatinine. This is found in the elderly, bedridden patients, muscle atrophy, patients who have undergone amputation, etc.

Malnutrition

Especially those lacking protein, improper weight loss, or anorexia, all of which reduce muscle mass and consequently lower blood Creatinine levels

Chronic liver disease

Patients with cirrhosis or certain chronic liver diseases have reduced Creatine synthesis, resulting in lower production of Creatinine

Pregnancy

Pregnancy increases the volume of body fluids, thereby reducing the concentration of Creatinine in the blood

Genetic abnormalities

Certain abnormalities such as Congenital Myopathies cause lower than normal production of Creatine and Creatinine

Certain medications that may affect Creatinine levels

Some medications may affect measurements resulting in lower Creatinine levels, such as diuretics or steroid drugs

Regularly check Creatinine, BUN, and eGFR to closely monitor kidney health

Checking Creatinine is one method to assess kidney function efficiency and screen for kidney abnormalities easily. It is usually necessary to measure BUN and eGFR together to increase accuracy of the assessment. One should regularly undergo kidney function tests and annual health check-ups to monitor, prevent, and treat kidney abnormalities from the early stage, and help reduce the risk of chronic kidney disease in the future

Because the kidneys are important organs for many systems in the body, maintaining good kidney health helps the kidneys function efficiently. Kidney Institute, Praram 9 Hospital, places importance on kidney health with services for measuring kidney function and performance, along with physical examinations to detect diseases that may increase the risk of kidney failure

For more information

Facebook : Praram 9 Hospital International & Expats

Line : @Praram9Hospital

Tel. 1270

Frequently asked questions about Creatinine

1. How should one prepare before a kidney function test?

In general, Creatinine testing does not require fasting from food or water, unless the doctor orders additional blood tests such as blood sugar or lipid tests that may require fasting in advance.

2. Can Creatinine levels change?

Creatinine levels can increase or decrease from many factors such as water intake, exercise, or medication use. This is usually a temporary condition and does not always indicate an abnormality.

References

Lewin R.N., J. (2025, March 27). What are normal levels of creatinine, and how are they tested? MedicalNewsToday. https://www.medicalnewstoday.com/articles/322380

Blood Urea Nitrogen (BUN) Test. (2022, November 11). Cleveland Clinic. https://my.clevelandclinic.org/health/diagnostics/17684-blood-urea-nitrogen-bun-test

Estimated Glomerular Filtration Rate (eGFR). (2025, May 2). Cleveland Clinic. https://my.clevelandclinic.org/health/diagnostics/21593-estimated-glomerular-filtration-rate-egfr

Higuera, V. (2024, August 12). What to Know About Low Creatinine. Healthline. https://www.healthline.com/health/low-creatinine