Accuracy of Glomerular Filtration Rate (GFR) Estimation Using Creatinine and Cystatin C and Albuminuria
Accuracy of Glomerular Filtration Rate (GFR) Estimation Using Creatinine and Cystatin C and Albuminuria
The eGFR-C study will assess the accuracy of current and alternative tests of kidney function
 against a reference test in people with moderate (stage 3) chronic kidney disease (CKD).
The eGFR-C study will assess the accuracy of current and alternative tests of kidney function
 against a reference test in people with moderate (stage 3) CKD. Participants will be
 recruited from hospital clinics and General Practitioner (GP) practices at six major United
 Kingdom (UK) centres.

 The best measure of kidney function is accepted to be the glomerular filtration rate (GFR),
 which measures the ability of the kidney to filter blood and is widely used in clinical
 practice. A low GFR suggests poor kidney function. An estimate of GFR can be obtained from a
 simple blood test.

 Participants will undergo reference GFR testing at study entry with a second follow-up
 reference test three years later. The reference test involves injecting a small amount of
 iohexol into a vein and taking blood samples over the next 4 hours to see how quickly the
 iohexol disappears from the blood stream as a result of glomerular filtration. The rate at
 which iohexol disappears is equivalent to the level of kidney function. Blood tests for
 monitoring kidney function, including testing for creatinine and cystatin C, and measurement
 of urinary albumin will be done every six months during the study period.

 Iohexol measured GFR will be accepted as the reference ('gold standard') measure of kidney
 function against which each GFR-estimating equations will be compared. The alternative
 estimated measures of GFR, derived from measuring substances (creatinine and cystatin C) in
 the blood, will be compared against the reference test. An important outcome is how much the
 reference test changes over the three years of the study, and how well the surrogate measures
 reflect this change.

 The investigators will also collect accurate test cost data for subsequent cost-effectiveness
 analysis (e.g. do the relative costs of the tests justify any change in practice due to
 improved performance of one test compared to another?).
Inclusion Criteria:

 -  Patients with stage 3 CKD (GFR 30-59 mL/min/1.73 m2) as defined internationally,
 diagnosed using MDRD/CKDEPI eGFR (at least two consecutive test results in this range
 at least 90 days apart, with the most recent test in the last 12 months)

 -  Aged 18 years or over

 -  Written informed consent

 Exclusion Criteria:

 -  History of untoward reactions to iodinated contrast media or allergy to topical iodine

 -  Episode of acute kidney injury in previous 6 months (as defined by the Acute Kidney
 Injury Network criteria)

 -  Amputation of whole or part-limb

 -  Pregnant or breastfeeding

 -  Known current alcohol or drug abuse

 -  Kidney transplant recipient

 -  Any condition with an expected survival of less than study duration

 -  Inability to comply with study schedule and follow-up

 -  Inability to provide informed consent e.g. due to cognitive impairment