Dr Jennifer Lees

Dr Jennifer Lees at the University of Glasgow, along with other researchers, have come up with a blood test to better measure the risk of both kidney and heart disease than what doctors use at the moment. This blood test gives a more definite diagnosis, which could lead to better health outcomes, and could easily be adopted by the NHS for routine testing.

Of kidneys and hearts

Chronic kidney disease (CKD) affects around one in ten people and it gradually reduces how well your kidneys work. It is also linked with early-onset heart disease and a higher risk of dying earlier. In some cases, CKD can damage the kidneys so much that you may need dialysis or a kidney transplant to survive.

For people living with CKD, being able to reduce the chances of also developing heart disease, relies on getting an accurate diagnosis, as well as identifying and then treating the associated risk factors.

Tests to spot changes in kidney health

Usually, doctors measure levels of something in your blood called serum creatinine, which changes depending on how well your kidneys are working. Serum creatinine is a waste product from muscle activity that your kidneys usually filter out. When your kidneys do not work as they're supposed to, because of something like CKD, serum creatinine builds up in the blood. That build-up can be detected with a blood test and it lets doctors know that there's something wrong with your kidneys.

Serum creatinine has been used for a long time and is the go-to test for looking at kidney health. However, this new research has thrown a different chemical into the spotlight: cystatin C. Just like serum creatinine, your kidneys normally filter out cystatin C from your blood and so can be used in the same way to spot changes in kidney health. Unlike serum creatinine, cystatin C is produced from all cells in the body, rather than just muscles, and so isn't affected by things like muscle mass or gender.

Cystatin C itself isn't new and has actually been available in UK NHS labs for over a decade. But cystatin C hasn't formed part of regular testing when it comes to looking for changes to kidney health.

Catching kidney disease earlier

Dr Jennifer Lees' work could be about to change that. Jennifer said: “Our findings indicate that patients would benefit from the added predictive value of using a test called the cystatin C test. We would hope to see it adopted as the primary method for diagnosis of chronic kidney disease – particularly for those patients with heart disease risk factors such as diabetes, hypertension or obesity.”

The study used records from over 400,000 patients in the UK Biobank and looked at three different kidney health tests to see which one gave the most accurate prediction of heart disease and the risk of an earlier death. They found cystatin C was best at predicting cardiovascular risk as compared to the more commonly used serum creatinine test.

The cost of accuracy

Testing for cystatin C costs 10 times more than serum creatinine – it costs £2.50 per test, compared with £0.25 for a serum creatinine test. As such, cystatin C is currently only used in specialised settings and is not available in all hospitals.

Dr Lees added: “Despite being recommended by the National Institute for Health and Care Excellence (NICE), measurement of cystatin C has not been widely adopted in clinical practice, presumably relating to uncertainty around the added value of a more expensive test.

“We hope our study shows that the adoption of this simple test would provide doctors with a precision medicine diagnosis for kidney disease and cardiovascular risk.”

The study, “Glomerular filtration rate by differing measures, albuminuria and prediction of cardiovascular disease, mortality and end-stage kidney disease”, is published in Nature Medicine. The work was funded by Chest, Heart and Stroke Association Scotland, the British Heart Foundation and Kidney Research UK.