GPs should use an additional blood test to confirm a diagnosis of G3a (formerly stage 3a) chronic kidney disease, under major new proposals designed by NICE to tackle the problem of misdiagnosis.
The current eGFR measurements based on creatinine have come under criticism for diagnosing too many people with stage 3 CKD, especially elderly people, leading NICE to issue guidelines incorporating an as yet widely unavailable new test to help GPs confirm stage 3a CKD.
Experts welcomed the proposal, which they said could cut the number of stage 3a diagnoses of CKD by up to 25%, although they cautioned that laboratories will need time to establish it as a routine measure, while GPs will need to adjust their QOF CKD registers.
One recent study found referrals for CKD went up 60% at an NHS Trust after expanded criteria for CKD came in.
As a result of widespread overdiagnosis, NICE has recommended the new test – eGFRcystatinC – which would be used to confirm stage 3a CKD where the initial creatinine-based eGFR reading suggests mild to moderately reduced kidney function, but the patient has no other markers of kidney disease.
To improve diagnosis, the draft guidance recommends a more refined classification of CKD, as previously adopted by the Kidney Disease Improving Global Outcomes (KDIGO) organisation, with each eGFR category subdivided into the three albumin-to-creatinine (ACR) categories <3, 3-30 and >30 mg/mmol.
The extra cystatinC-based eGFR test would be ordered for patients with an initial creatinine-based eGFR of 45-59 ml/min per 1.73 m2 but no proteinuria, as indicated by an ACR of less than 3 mg/mmol, to confirm a diagnosis of G3a (formerly stage 3a) CKD.
Professor Donal O’Donoghue, honorary professor of renal medicine at the University of Manchester, said the updated guidance would provide an ‘important refinement’ to the classification system and the new cystatinC test would begin to address the problem of misdiagnosis of early-stage CKD.
He said: ‘The [draft] guideline recommends an important refinement to the classification system. In addition to looking at urine albumin- creatinine ratio, which is as, if not more, important than the creatinine based eGFR, the guideline recommends that in people with stage 3a CKD who don’t have proteinuria that serum cystatin C is measured and that laboratories report cystatin-based eGFR.
‘This change begins to address the misdiagnosis that can occur in CKD 3a which has always been the trickiest group to classify. It is likely to remove up to 25% of those who could be labelled with CKD 3a applying the older guideline.’
Professor O’Donoghue added: ‘This improvement in diagnostic accuracy will be rightly welcomed by patients and those who have argued that the simple cut off at creatinine eGFR is too simplistic, but laboratories will need time to establish cystatin C as a routine measure and GPs will need good notice to readjust their CKD QOF registers – and time to explain the changes to their patients.’
Dr John Ashcroft, GPSI in Derbyshire, said the new approach would help to prevent misdiagnosis and should prove cost-effective.
Dr Ashcroft said: ‘I have been concerned about just how many patients are certainly being diagnosed with CKD, on the basis of eGFR, when they do not have it, and also underdiagnosed.
‘This is a problem especially for the elderly and obese where eGFR is less reliable and can result in patients being given diagnosis they don’t have, and made unnecessarily worried.
‘It can prevent them from being given some medications, such as nitrofurantoin and NSAIDs, and also mean they get treated to lower blood pressure targets when that wouldn’t otherwise be justified. Also, because CKD increases CVD risk significantly, CVD risk assessment will often indicate that they should be on a statin.’
He added: ‘Though the test is 10 times the price of serum creatinine, it is only £2.50, so actually in the greater way of things very cheap.’
NICE CKD guidance draft updates – key recommendations
Consider using eGFRcystatinC to confirm the diagnosis of CKD in people with:
- an eGFRcreatinine of 45 –59 ml/min per 1.73 m2, sustained for at least 90 days and
- no proteinuria (albumin: creatinine ratio [ACR] less than 3 mg/mmol).
Do not diagnose CKD in people with:
- an eGFRcreatinine of 45–59 ml/min per 1.73 m2 and
- an eGFRcystatinC of more than 60 ml/min per 1.73 m2 and
- no other marker of kidney disease.
Classify CKD using a combination of GFR and ACR categories. Be aware that:
- increased ACR is associated with increased risk of progression
- decreased GFR is associated with increased risk of progression
- increased ACR and decreased GFR in combination multiply the risk of progression.