Comparison of Markers of Kidney Function

Comparison of Estimated GFR Using Cystatin C Versus Creatinine in Pediatric Renal Transplant Patients

Glomerular filtration rate (GFR) is the best known measurement of kidney function. Serum creatinine (blood test) is the most commonly used marker to predict GFR. It is a convenient, inexpensive test that involves a single blood draw with rapid results. However, creatinine has several limitations because its blood level is dependent on age, body mass, and sex. One of the gold standards for measuring GFR is plasma clearance of an IV injected agent, iohexol. It has been found to be safe and nontoxic in prior studies, but is not practical in the clinical setting due to the need for several timed blood draws. Recent studies have investigated the use of cystatin C as an alternative marker to predict GFR. Cystatin C also involves only a single blood draw, and has less confounding factors than creatinine since it is independent of age, body mass, and sex. Currently, it remains controversial whether cystatin C is a significantly better biomarker of estimated GFR than creatinine. To date, there has not been a large prospective cohort study to compare cystatin C and creatinine in pediatric kidney transplant patients who are on maintenance immunosuppression (anti-rejection drugs). Accurate measurement and early detection of deterioration of GFR is critical in the care of this patient population. The purpose of this study is to assess the accuracy of estimating GFR by using cystatin C versus creatinine clearance equations when compared to the surrogate gold standard of iohexol GFR in pediatric renal transplant patients.

Study Overview

• Status: Completed
• Conditions: Renal Insufficiency; Chronic Kidney Disease

Detailed Description

Study patients will come in for their surveillance biopsy done as standard of care post-transplant. They we be made NPO at midnight prior to the biopsy per routine. On arrival, they will have standard of care pre-biopsy bloods drawn along with baseline study labs including serum enzymatic creatinine (1mL of blood), cystatin C (1.5 mL of blood), and 1mL of blood collected pre-iohexol infusion. Two IV's will be started, one for iohexol administration and fluids, and the other for blood draws. Study patients will be started on 1x maintenance intravenous fluids. The patient will then have their standard of care protocol biopsy in the ultrasound suite. After the biopsy 5 mL Iohexol (Omnipaque 300) will be administered over 1-2 minutes, with epinephrine, solumedrol, and diphenhydramine on hand in the event of a reaction although this is very unlikely. The patient will be observed and vital signs will be taken 10 minutes post-infusion. After biopsy, maintenance fluids will be continued until completion of the study. Blood for determination of Iohexol levels (1mL) will be drawn at 10, 30, 120, and 300 minutes post iohexol infusion when patient is being observed post biopsy. At completion of the study at 300 minutes post iohexol infusion, serum creatinine (1mL of blood), cystatin C (1.5 mL of blood) will be drawn again. The total volume of blood drawn for the study will be 10mL.

Creatinine (enzymatic method) will be determined on the Olympus system, and Cystatin C (Gentian assay) will be determined on the AU400 Olympus System at the UCLA Department of Pathology and Laboratory Medicine Outreach Laboratory. Iohexol GFR will be determined at the University of Rochester Medical Center in Dr. Schwartz's laboratory. Kidney biopsies will be graded by updated Banff criteria, and reviewed by blinded pathologist.

• Study Type: Observational
• Enrollment (Actual): 17

Contacts and Locations

Study Locations

• United States
  • California
    • Los Angeles, California, United States, 90095
      • University of California, Los Angeles

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: 1 year to 18 years (Child, Adult)
• Accepts Healthy Volunteers: No
• Genders Eligible for Study: All

• Sampling Method: Non-Probability Sample

Study Population

Subjects will be recruited from UCLA pediatric kidney transplant patients with stable allograft function that come in for routine surveillance biopsy. Patients will be induced with either daclizumab, basiliximab, or thymoglobulin and maintained on tacrolimus, mycophenolate mofetil, and steroid-free or steroid-based immunosuppression.

Description

Inclusion Criteria:

• Renal transplant patient aged 1 to <19 years old
• Stable allograft function (no history of biopsy proven acute rejection or increase of creatinine of > 10% from baseline in the past 6 months)
• No changes in maintenance immunosuppression in the month before the protocol biopsy
• Subject and/or parent must be able to understand and provide informed consent

Exclusion Criteria:

• Biopsy proven acute rejection in the past 6 months
• Change in maintenance immunosuppression in the month before the protocol biopsy
• Known diabetes mellitus
• Known thyroid dysfunction
• Allergy to Iohexol or other contrast media
• Inability or unwillingness of a participant or their legal guardian to give written informed consent or comply with the study protocol

Study Plan

How is the study designed?

Number of groups / cohorts

1

Cohorts and Interventions

Group / Cohort
Pediatric post-kidney transplant; Patients having standard of care surviellance biopsies.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Time Frame
The primary outcome measure is a comparison of determination of GFR through three methods: cystatin C (Gentian assay), creatinine (Schwartz and update Schwartz) and iohexol disappearance	Participants will be followed for the duration of the Iohexol GFR measurement (approximately 8 hours) that will take place at the time of surveillance biopsy at either 6 months, 1 or 2 years post-transplant..

Collaborators and Investigators

• Sponsor: University of California, Los Angeles
• Collaborators: Gentian

Study record dates

Study Major Dates

• Study Start: August 1, 2011
• Primary Completion (Actual): December 1, 2012
• Study Completion (Actual): December 1, 2012

Study Registration Dates

• First Submitted: July 25, 2011
• First Submitted That Met QC Criteria: July 26, 2011
• First Posted (Estimate): July 27, 2011

Study Record Updates

• Last Update Posted (Actual): November 17, 2020
• Last Update Submitted That Met QC Criteria: November 16, 2020
• Last Verified: November 1, 2020

More Information

Terms related to this study

• Keywords: transplant; pediatric; kidney; cystatin C; creatinine; GFR; iohexol
• Additional Relevant MeSH Terms: Urologic Diseases; Kidney Diseases; Renal Insufficiency, Chronic; Renal Insufficiency
• Other Study ID Numbers: Gentian-Cystatin-UCLA