Participants: Greg Miller, Andrew Narva, Eileen Newman, Lorin Bachmann, David Bruns, David Bunk, Gary Curhan, Joris Delanghe, John Eckfeldt, James Fleming, Mariastella Graziani, Neil Greenberg, Glen Hortin, Chandra Jain, David Koch, Anthony Killeen, John Lieske, Matthew McQueen, Gary Myers, Mauro Panteghini, Karen Phinney, James Ritchie, Mary Robinson, Sverre Sandberg, George Schwartz, David Seccombe, Lesley Stevens, Jack Zakowski, Harvey Kaufman, and Nancy Accetta.
1. Membership review
Greg explained that the call was a joint meeting of the NKDEP Laboratory Working Group (LWG) and two International Federation of Clinical Chemistry (IFCC) groups – Standardization of Urinary Albumin (WG-SAU) and Glomerular Filtration Rate Assessment (WG-GFRA), which is headed by Neil Greenberg. Greg introduced Lesley Stevens, Tufts New England Medical Center, as a new member of the LWG and the lead on an NKDEP group developing provider guidelines on CKD and drug dosing. Maria Graziani was introduced as an IFFC WG-SAU corresponding member from Verona, Italy. There is substantial overlap in membership in these three groups.
2. Project status reports
- Creatinine specificity (LWG and IFCC WG-GFRA; NKDEP sponsor)
Neil Greenberg explained that the data collection phase is almost finished, having collected samples across pathological groups at the Medical College of Virginia and the University of Utah Medical Center. More than 430 samples were collected, split into aliquots, and then sent to four manufacturers: Ortho Clinical Diagnostics, Roche Diagnostics, Siemens, Beckman-Coulter. Each manufacturer is using its own methods, some using multiple methods, including Jaffe and enzymatic. Aliquots were also sent to a laboratory in London, which is using an LC Mass Spectometry method. Data should be back by March 13, and the investigation will enter data analysis phase. Anticipate reporting results at the NKDEP LWG meeting in Chicago in July 2009.
- Urine albumin container adsorption study (LWG and IFCC WG-SAU; CDC sponsor)
Mary Robinson had circulated a draft experimental design and protocol that is intended to integrate most of the factors known to influence surface adsorption, and allows monitoring of albumin concentration on the same samples stored for different periods and temperatures in different containers. Containers have been ordered, and CDC IRB documents have been submitted. Upon review of the protocol, participants are asked to send Mary insights and suggestions for improving the protocol before the study begins. Questions are also invited.
- Urine albumin biologic variability study (LWG and IFCC WG-SAU; CDC sponsor)
Study objectives are to: 1) determine which urine sample collection method is the most practical and the least variable for urinary albumin measurement, and 2) document the intra-individual variability, both short-term (3 months) and long-term (12 months). Protocol is nearly completed by investigators at CDC. Goal is to enroll subjects and complete 3-month protocol by December 31, 2009. Urine sample collection is to begin in May; an update and a report should follow in July 2009 and July 2010, respectively. Mary shared details regarding recruiting and patient requirements. Please contact Mary at CDC with questions.
3. Projects in development
- NKDEP/CRIC mechanism for funding LWG projects
Andrew Narva described the mechanism for obligating funds made available by NIDDK to complete LWG projects related to measurement of kidney function and kidney damage. The funds were made a supplement to the Chronic Renal Insufficiency Cohort (CRIC) study based at the University of Pennsylvania. Projects will be completed by LWG investigators funded as sub-contractors to CRIC. Two projects have started: the first is the creatinine specificity study; the second will be a validation of the new pediatric estimating equation in children with near-normal kidney function. All funds must be allocated by the end of FY 2009.
- Evaluate CKiD equations with Jaffe methods
George Schwartz stated that the investigators are currently determining the exact level of funding required for this study. New formulas for estimating GFR in children are published in the March issue of the Journal of the American Society of Nephrology. Formulas were generated using IDMS reference-based enzymatic serum creatinine methods. The equation that works best includes creatinine, B.U.N., and Cystatin C, along with some anthropometric measurements, particularly for gender and height. Equations work very well and have allowed the CKiD study to perform estimates every other year instead of yearly iohexol-based GFR studies. What is bothersome about this recent study: equation derived from children with significant kidney impairment (Stage 3, on average, with a mean GFR of 40). When we do a lot of screening in pediatrics, we need something useful for children in the upper end of function (e.g., GFR around 80-90). The recently published formulas did not appear to have been generated with anyone with a GFR above 80, so we wanted to extend the study to include children who are fully grown, fully mature, and not lagging behind in height percentiles, with GFRs in the high range. These studies include children with an average height percentile of 23; and only 25% of the population being fully mature. We plan to recruit 100 children to try and extend the current formulas using the CKiD network; and we will limit the study to a few sites to save on shipping/handling. George noted Greg's recommendation to use not only the enzymatic creatinine method, but also look at the Jaffe, which is referenced to IDMS standards. Also, the Cystatin C assay was a turbidimetric assay (Dako), which yielded data that showed poor correlation with GFR. Investigators worked with Siemens/Dade Behring to get a loaner BN2 nephelometer. For first 100 children in CKiD II, the correlation with the reciprocal of Cystatin C is much tighter than it had been with the Dako analyzer; they are very optimistic this method will give even better estimate formulas for children. CKiD will underwrite cost of trying to reconcile original Dako assay measurements with what will be performed with new analyzer.
- Assessment of urine albumin/creatinine measurement harmonization
Lori Bachman explained that the goal of the project, which is in the planning stage, is to compare urine albumin and creatinine measurements among the different manufacturers' routine methods to assess their level of harmonization. The study will utilize freshly collected native patient urine samples in clinically useful albumin concentration ranges. The proposal calls for collecting samples from at least three sites at a sufficient number to include clinically relevant disease processes and a variety of commonly encountered urine matrices. The study group held its first call and is preparing the protocol, which should be finished in the next few months. Next steps include approaching manufacturers to secure their participation, obtaining IRB approvals, and submitting the project for funding. Likely study sites include Virginia Commonwealth University (Greg Miller/Lori Bachmann), McMaster University (Matt McQueen), and the University of Virginia (David Bruns); although there may be others. The protocol will be distributed for review and comment before the LWG meeting in Chicago, at which time an update will be provided.
- ID-LC-MS method for urine albumin
John Lieske reported that he and his colleagues at the Mayo Clinic have completed validation of a trypsin digestion LC-MS-MS assay, which still uses an N15-labeled albumin as an internal standard. The study showed that this assay had a much improved performance over the end-source fragmentation assay previously presented. With this, they can get down to a limit of quantification which is about 3mg/L—comparable to the immunoturbidimetric assay used in the Mayo clinical laboratory. Comparisons between the new LC-MS/MS assay and the standard immunosassays in the Mayo clinical laboratory had good correlation, although some calibration issues were apparent. The Mayo team was also able to do some comparisons with samples sent to Glen Hortin (when at NIH). Again, results with the LC-MS assay were very comparable to those with two different immunoassays. Based on the sum of Mayo's data, they don't see any evidence for interference in most urine samples with either fragments of albumin or with the immunounreactive albumin that had been hypothesized previously. They don't see a reason to move ahead with LC-MS/MS as a routine clinical assay, since as long as immunoassays are properly calibrated, they should be accurate for the clinically relevant ranges of albumin. John and colleagues are currently exploring practicalities for developing this as a reference method, but resources are limited. They are discussing funding with David Bunk and collaborators. The Mayo team expects their paper describing the assay to be published in Clinical Chemistry (Clin Chem) very soon; a paper for the comparison study with Glen Hortin is under development.
- Development of a urine creatinine reference material (NIST)
Karen Phinney commented that NIST is procuring a pool of urine to use as a prototype material to help with method development. NIST welcomes input from the group in regards to the study protocol. First goal is to see if existing methodology can be adapted. They asked for a minimum of 10 donors who were free of overt disease, without requirements around time of urine collection, etc. (This may be an agenda topic for the LWG meeting in Chicago.) Glen Hortin mentioned how the samples should be freshly collected, that the matrix could be affected by freezing and storage conditions, and that we may need to establish a common standard practice in laboratories. David Bunk stated that a reference material needs to be stored under conditions that are stable over time.
- Urine albumin secondary reference material (by JSCC)
Yoshi Itoh had communicated to Greg that the Japanese standardization project is continuing and he will attend the July LWG meeting in Chicago. Greg and Yoshi are exploring an English-language paper to report the full characterization of this reference material.
- Other projects needed?
- A potential project that needs a champion: search databases for a range of urine constituents that are found in urine as a way to catalogue different kinds of matrix components that an albumin or creatinine method would need to handle without undue influence.
- Other project ideas should be sent to Greg Miller or Nancy Accetta for consideration by the larger group.
- Drug dosing group
Andrew Narva explained that this group was formed because clinical settings cannot use standardized creatinine in the Cockcroft-Gault (CG) estimating equation, which is traditionally used for drug dosing calculations and decisions. A document intended to inform health care providers on this issue is being drafted and will be circulated for comment by the end of April. Andy noted that most questions on this issue are related to dosing carboplatin. A gynecological oncology group has promoted a single correction to back-calculate standardized creatinines to non-standardized creatinines, which can then be inserted into the CG for purpose of dosing carboplatin. While this process may be flawed, it emphasizes the educational challenge of getting providers to think in a new way about kidney function and drug dosing. Because carboplatin has a narrow therapeutic index, our colleagues at FDA have agreed to look at some of the original drug safety data in an attempt to generate estimated GFRs from the creatinine measurements that were obtained when the drug was initially submitted. This will help inform the document we are writing. NKDEP is fortunate to have Lesley Stevens, an expert in estimating kidney function for the clinical setting providing direction to this group. (This is a possible agenda item for July LWG meeting in Chicago.)
- Urine albumin recommendations published (Clin Chem 2009;55:24-38)
- Dutch EQA creatinine interferences published (Cobbaert et al. Clin Chem 2009; 55:549-558)
Dutch EQA included in one of their surveys last year a set of samples that had spiked in well-characterized creatinine Jaffe method interfering substances.
- CKiD pediatric eGFR equations (Schwartz et al. J Am Soc Nephrol online Jan 21)
As George reported, the revised equations have been published (since agenda was circulated); J Am Soc Nephrol 2009;20:629-637.
- CK-EPI adult eGFR equation (abstract at ASN meeting, November 2008)
Lesley Stevens reported that the paper has been accepted.
- Cystatin standardization (by IFCC WG-SCC)
Greg reported on Anders Grubb's behalf that this work group has prepared a statement summarizing the status of standardization that will be posted on the NKDEP website. They are hoping to have secondary standard reference material fully characterized in the near future, with the product being distributed by IRMM (Belgium) sometime this year. This will allow Cystatin C manufacturers to have a traceable calibration scheme.
- The group discussed whether or not Cystatin C would become a component of some routine testing panels. Current issues include reimbursement and lack of standardization. Greg stated that the LWG would welcome the opportunity to be represented on committees developing clinical guidelines on testing recommendations.
5. NKDEP website updates and needs
- Nancy Accetta reported that the NKDEP website's Lab Professionals section has undergone some changes in the last year. Eileen Newman thanked those on the call who participated in paper-based usability testing that NKDEP recently conducted to identify areas for improvement. Nancy invited participants to call or write to NKDEP if they would like to see content added to the site or have suggestions for improving it.
- Add content to inform those unaware of the current limitation of using non-standardized Cystatin-based equations in the general population setting. The new CKiD pediatric equation hasn't been validated for use with people with normal GFRs.
- The term "serum creatinine" is used on the NKDEP site almost exclusively. It has come to Greg's attention that those using whole blood devices are confused by this term. He suggested replacing "serum creatinine" with "creatinine measured in blood." A problem may also exist in regards to those using point of care measurement. The web terminology will be reviewed with these concepts in mind.
- A way to rapidly include "what's new" information.
- Greg invites members to advise NKDEP on publications (citations) that should be posted on our site as resources for laboratory professionals.
6. LWG joint meeting at AACC with IFCC WG-GFRA and WG-SAU (Chicago, July 22, 2009, Wednesday, 1:00 p.m. – 5:30 p.m.)
- LWG session and Manufacturer's Forum
The group supports the format previously used: NKDEP LWG meeting, followed by the Forum to update manufacturers on current issues. Greg noted that we have been aggressive with the agenda in years past and recommended that this year's meeting focus on topics that require group discussion.
- Manufacturers participating in the specificity study will be invited to the LWG meeting.
- Forum will last only one hour – presenting an update of the various activities to the manufacturers.
- Proposed agenda items
- NIST reference material for urine creatinine and possibly urine albumin; the drug dosing recommendations; update on specificity study (e.g., results and recommendations, with a high-level summary for the Forum); urine adsorption study (10 minutes); possibly a Cystatin C report by Anders Grubb or colleague (Gary Myers will ask the IFCC Scientific Division for an update and report back to the LWG).
- David Bunk will contact Dr. Itoh to coordinate his team's work on the UA reference material.
- We will ask for project updates in writing so they can be circulated with the agenda before the meeting, and not have formal presentations. This format will allow time for questions and discussion.
- Content for website.
- Updated pharmacy and drug dosing recommendations
- CKD-EPI equation for eGFR
- Accetta NA, Gladstone EH, DiSogra C, Wright EC, Briggs M, Narva AS. Prevalence of estimated GFR reporting among US clinical laboratories. Am J Kid Dis2008;52:778-787. (Special Article)
- Miller WG. Reporting estimated GFR: a laboratory perspective. Am J Kid Dis 2008;52:645-648. (Editorial)
- Miller WG, Bruns DE. Laboratory issues in measuring and reporting urine albumin. Nephrol Dial Transplant 2009;24:717-718. (Editorial Comment)
- William E. Harmon WE. Glomerular Filtration Rate in Children with Chronic Kidney Disease. Clin Chem 2009;55:400-401. (Perspective)
- Miller WG. Estimating Equations for Glomerular Filtration Rate in Children: Laboratory Considerations. Clin Chem 2009;55:402-403. (Perspective)
- Sviridov D, Hortin GL. Urine Albumin Measurement: Effects of Urine Matrix Constituents. Clin Chim Acta, in press.