The kidney failure risk equation (KRFE) helps predict a person’s risk of kidney failure. Doctors may use it to guide treatment decisions for people with mid to late stage chronic kidney disease (CKD).
The insights the KFRE provides can help people with CKD take steps to slow the progression of their kidney disease, potentially delaying the need for dialysis or a kidney transplant.
As the National Kidney Foundation (NKF) explains, the KFREs are mathematical equations that help predict a person’s risk of developing kidney failure within 2 or 5 years.
These predictions use individual variables, such as a person’s age, sex, and individual kidney function.
Dr. Navdeep Tangri and colleagues first developed the KFRE in 2011. Since then, researchers have validated it using data from more than 700,000 participants in 30 countries worldwide.
Doctors now use the KFRE to predict the likelihood of kidney failure in people with CKD stages
According to the NKF, there are two types of KFRE, and each considers different variables.
The four-variable KFRE takes into account:
- Age: Kidney function typically declines with age. However, among those with CKD, younger people may be more likely to reach kidney failure faster.
- Sex: CKD is more common among females than males. However, males with CKD tend to progress to kidney failure sooner than females with CKD.
- Estimated glomerular filtration rate (eGFR): This is a measure of how effectively the kidneys filter waste from the blood.
- Urine albumin-to-creatinine ratio (UACR): This is a measure of two substances in urine: a protein called albumin and a waste product called creatinine.
The eight-variable KFRE takes into account the above four variables but also considers blood levels of the following substances:
- Bicarbonate: This substance prevents the body from becoming too acidic. Low blood levels of bicarbonate are associated with a faster onset of kidney failure.
- Albumin: Albumin helps balance fluid levels and carries important substances throughout the body. In CKD, low blood levels of albumin are associated with an increased risk of kidney failure.
- Phosphorus: Phosphorus is an essential mineral for bone and muscle health. High blood levels of phosphorus may damage the kidneys and impair kidney function.
- Calcium: Calcium is essential for bones and for muscle and nerve function. In CKD, the kidneys are less able to activate vitamin D for the body to absorb calcium, and low blood levels of calcium are associated with a faster onset of kidney failure.
To use the KFRE, a doctor will need to order blood or urine tests to determine the person’s kidney function variables. They will then use an online KFRE calculator to plug the variables into the equation. Doctors may choose between the four-variable KFRE and the eight-variable KFRE.
The KFRE calculates the likelihood that the person with CKD will progress to kidney failure within the next 2 or 5 years, depending on the timescale the doctor specifies. It expresses this prediction as a percentage or range of percentages from 0% to 99.99%.
A 2020 study describes the KFRE as the most widely utilized and easily accessible kidney failure prediction tool, with extensive validation from researchers and clinicians alike.
However, most of the research into the validity of the KFRE focuses on the transition from 3a or 3b CKD to kidney failure.
As a result, the authors of the 2020 study set out to investigate the effectiveness of the KFRE in predicting the transition from advanced CKD to kidney failure.
They conclude that the KFRE provided “adequate to excellent” discrimination in identifying individuals with stage 4 or 5 CKD who were likely to progress to kidney failure at the 2-year and 5-year time points.
Although the eight-factor KFRE involves more variables than the four-factor version, a
The researchers added that both equations were more useful in guiding treatment decisions than using eGFR alone.
The UK Kidney Association (UKKA) notes the following three limitations of the KFRE:
- The use of eGFR and UACR as predictive variables: The eGFR and UACR variables do not always accurately indicate kidney function. For example, having acute kidney injury or extreme weight or muscle mass can affect eGFR, and a urinary tract infection can affect UACR.
- Discounting other comorbidities: The KFRE does not take into account a person’s risk of dying from other comorbid conditions over the next 2 to 5 years.
- Limited validation for specific kidney diseases: Kidney disease has many potential causes that may influence its progression rate. Researchers have yet to establish the validity of the KFRE for conditions such as glomerulonephritis, cystic kidney disease, and vasculitis.
A person should contact a doctor if they have CKD and experience any symptoms of worsening kidney failure. These may include:
- weakness or fatigue
- swelling in the hands, feet, or ankles
- cramping in the hands and legs
- nausea and vomiting
- itchy skin
- shortness of breath
- headaches
- increased frequency of urination
- blood in the urine
- difficulty sleeping
A person should also contact a doctor if they have not yet received a diagnosis of CKD but have concerns about their kidney function. A doctor can order blood and urine tests to check their kidney function, and they can discuss appropriate treatment options if necessary.
Doctors can use the KFRE for people with CKD stages 3a through 5.
People with stage 1 or 2 CKD have minimal kidney damage and near-normal kidney function, meaning that their kidney function variables are likely to be close to the typical range. As a result, the KFRE is less valuable as a tool for predicting CKD progression.
The KFRE can predict kidney failure risk at 2 years and 5 years into the future.
The KFRE is primarily a tool for researchers and clinicians.
However, people with CKD stages 3a, 3b, 4, or 5 can use the KFRE on websites such as the Centers for Disease Control and Prevention (CDC) if they have the necessary information.
According to UKKA, a doctor should recalculate the KFRE at least once a year for people with CKD and more frequently for those with advanced kidney disease.
The KFRE is a mathematical equation that helps predict the risk of kidney failure in people with CKD stages 3a through 5. A doctor may use the KFRE to better inform people about their outlook and help guide treatment decisions.
The KFRE is primarily a tool for researchers and clinicians, though people with CKD stages 3a through 5 may want to use the tool to open up discussions with their doctor about treatment options and ongoing care.
A person may also want to talk with a doctor if they have CKD and experience symptoms of worsening kidney function, or if they do not have a diagnosis of CKD but have concerns about their kidney function.
