Accurate CKD monitoring using postal iohexol mGFR v1.0
Research type
Research Study
Full title
Improving the accuracy of chronic kidney disease monitoring using postal finger prick iohexol measured GFR
IRAS ID
304466
Contact name
Darren Green
Contact email
Sponsor organisation
Northern Care Alliance NHS Foundation Trust
ISRCTN Number
ISRCTN14717076
Duration of Study in the UK
1 years, 6 months, 1 days
Research summary
Summary of Research
Blood tests are not always accurate because they estimate rather than measure kidney function. Harm can come through inaccurate kidney function estimates.
People of certain ethnicities are more vulnerable to incorrect estimates of kidney function using standard blood tests. This can contribute to health inequality. This means there needs to be other, better ways to check kidney function to ensure that everyone gets the right treatment at the right time.
The gold standard kidney test is to give an injection of a molecule into a vein and then measure the level of the molecule a number of hours apart to tell how quickly it is leaving the body. Unfortunately, blood tests need to be taken for up to 6 hours after the injection. This makes the test very challenging for many patients and impractical for regular use by hospitals.
The proposed study will evaluate performing a gold standard test in a user-friendly way. A blood test for one of the molecules used in the gold standard test (called iohexol) can now be done using a small finger prick sample. This is like when people with diabetes check their own blood sugars and the “newborn blood spot test”. Like these, the iohexol microsampling test could be done by people at home. This iohexol test involves an injection of 5mL of iohexol into a vein (one teaspoon) during a clinic visit and then undertaking a fingerprick test three times at home 3, 4, and 6 hours after the injection. The three microsamplers can then be posted to the kidney test laboratory for analysis to very accurately measure kidney function.
Ultimately, the quality, safety and comfort of care that kidney clinics can provide will be improved if we are able to show that home measurements of GFR are possible.Summary of Results
Creatinine is the blood test that we take to help us estimate kidney function. From a blood creatinine level we derive eGFR values, which are used to monitor kidney health. This determines referral to renal services, treatment plans, drug dosing, and dialysis and transplant planning. Unfortunately, creatinine is not a perfect test and it can contribute to health inequality because it is less accurate in estimating GFR in minority ethic patients, some socially vulnerable groups, and people with very low or very high muscle mass. This is shown in the picture below.
Inaccurate eGFR can lead to delays in care and incorrect drug dosing with potential to cause harm.
It is possible to measure rather than estimate kidney function in clinical practice but this has historically only been possible using a type of scan in hospitals which is expensive, time consuming (up to 6 hours), and that has atypical waiting time of 2 months.
In renal research, there is another way of measuring kidney function that involves having an injection of a compound called iohexol and then measuring its level in the blood 2 to 3 times a few hours after the injection. The kidneys clear iohexol from the blood, so by looking at how the level in the blood drops over time, you can very accurately measure kidney function. This is called iohexol mGFR testing and is recognised as a gold standard method of measuring kidney function.
We have developed and tested a way for people coming to renal clinics to have an injection of iohexol when they are there and then go home and take fingerprick blood tests themselves that can be posted back to us so we can measure iohexol levels. These fingerprick bloods are similar to doing blood glucose monitoring in diabetes. We have tested this approach in 40 patients.
In 37 cases, the home testing kit gave mGFR values which were the same as the gold standard experimental testing approach. In our participant feedback 60% described self-testing as ‘easy’ or ‘very easy’ and 66% would be willing to perform self-testing ‘frequently’ (every few weeks) or ‘often’ (every 1-3 months).
Although not yet perfected, this initial proof of concept study has given very encouraging results. Potentially, we can measure rather than estimate kidney function when we think that creatinine may not be sufficiently accurate in a way that is not overly burdensome for patients and which does not come at high cost to the NHS. This could improve the timeliness of care planning for people living with CKD and benefit in other people such as ensuring accurate drug dosing for cancer patients.
Our next step is to apply to the NIHR for a grant to undertake much larger scale evaluation of improving the testing kit and understanding how it best fits into clinical practice and what the real life impact and benefit could be.REC name
West of Scotland REC 4
REC reference
22/WS/0016
Date of REC Opinion
25 Feb 2022
REC opinion
Further Information Favourable Opinion