Staging and risk stratification
CKD Classification
A patient is said to have chronic kidney disease (CKD) if they have abnormalities of kidney function or structure present for more than 3 months.
The definition of CKD includes all individuals with markers of kidney damage (see below*) or those with an eGFR of less than 60 ml/min/1.73m² on at least 2 occasions 90 days apart (with or without markers of kidney damage).
- *Markers of kidney disease may include: albuminuria (ACR > 3 mg/mmol), haematuria (of presumed or confirmed renal origin), electrolyte abnormalities due to tubular disorders, renal histological abnormalities, structural abnormalities detected by imaging (e.g. polycystic kidneys, reflux nephropathy) or a history of kidney transplantation.
CKD Classification
CKD is classified based on the eGFR and the level of proteinuria and helps to risk stratify patients.
Patients are classified as G1-G5, based on the eGFR, and A1-A3 based on the ACR (albumin:creatinine ratio) as detailed below:
For Example
- A person with an eGFR of 25 ml/min/1.73m² and an ACR of 15 mg/mmol has CKD G4A2.
- A person with an eGFR of 50 ml/min/1.73m² and an ACR of 35 mg/mmol has CKD G3aA3.
It is important to note that patients with an eGFR of >60 ml/min/1.73m² should not be classified as having CKD unless they have other markers of kidney disease (see above*).
Patient information
Patients with CKD can be classified depending on their level of kidney function, or eGFR, and the amount of protein present in the urine. This information forms the basis of CKD staging which is useful for planning follow up and management. The higher the stage (G1->G5) and the greater the amount of protein present in the urine (A1->A3) the more “severe” the CKD and the higher the risk that a patient may develop renal failure requiring dialysis in the future.
Kidney Failure Risk Equation (KFRE)
What is the Kidney Failure Risk Equation?
The Kidney Failure Risk Equation (KFRE) is a well-validated risk prediction tool for a kidney replacement therapy (KRT) in the next two or five years in individuals with chronic kidney disease (CKD) stages 3a-5.
To estimate the risk of KRT, the four-variable KFRE uses:
- Age
- Sex
- Estimated glomerular filtration rate (eGFR)
- Urine albumin:creatinine ratio (ACR)
The KFRE has been re-calibrated specifically for the UK population and is available via this website. Please note that this may be different from some other publicly available calculators.
When should the Kidney Failure Risk Equation be calculated?
The KFRE should be calculated when an individual with CKD Stage 3a-5 has an eGFR and ACR measured. This should be at least on an annual basis, but more frequently with more advanced disease (see the frequency of monitoring section of management of patients with CKD). We would recommend that both eGFR and ACR should be within six months of each other, and ideally within a month.
How will the Kidney Failure Risk Equation improve care for my patients?
- The UK re-calibrated KFRE has recently been recommended by NICE to guide personalised care for people with CKD stages 3a-5 including referral to secondary care. If the risk of KRT is >5% in the next 5 years, referral should be considered factoring in the patient’s ‘wishes and comorbidities’. This threshold has replaced the previous recommendation for considering referral if eGFR is less than 30 ml/min/1.73m². This is because it is likely to be more sensitive and specific for KRT and may reduce the number of people referred unnecessarily.
- Two-year predictions may be more applicable to secondary care when discussing the risk of requiring KRT over a shorter timeframe and planning for procedures such as fistula formation or transplant listing.
How do I communicate Kidney Failure Risk Equation scores with patients?
Discussing KRT risk with should follow NICE’s guidelines for ‘shared decision making’ and should include:
- Discussing KRT risk in the context of a patient’s life, such as comorbidities and what matters most to the patient
- Describing KRT risk over the appropriate timeframe using ‘natural frequencies’ such as ’10 in 100′, instead of percentages such as ‘10%’
- Use a mixture of numbers and pictures
What are some limitations of the Kidney Failure Risk Equation?
- As KFRE uses eGFR and urine ACR to make a prediction, the same limitations for eGFR and urine ACR are also applicable to KFRE. Examples include assessment of patients at extremes of weight or muscle mass, or where a patient is being assessed in the context of acute kidney injury, or for ACR where a patient has a urinary tract infection. Please see the measurement of kidney function sections on eGFR and albuminuria for further explanation.
- KFRE should always be viewed in the context of the individual, their comorbidities, and their risk of dying from other causes over a period of the next two/five years.
- There has been limited specific validation of the KFRE in primary renal pathologies such as glomerulonephritis, cystic kidney disease and vasculitis. Therefore, in these groups caution should be used when making predictions based on KFRE.
More detailed information on KFRE including its development is available here.