The CAP has 30 official liaisons to various organizations who attend scientific meetings or designate others to do so. They report to the Standards Committee, which reports to the Council on Scientific Affairs. We periodically publish bits of what the CAP’s outbound liaisons hear and see in their liaison roles.
Standardizing urine albumin measurement procedures
W. Greg Miller, PhD and Lorin Bachmann, PhD
November 2016—The Laboratory Working Group of the National Kidney Disease Education Program and the IFCC Working Group for Standardization of Albumin in Urine are collaborating with IVD manufacturers to improve standardization of commercial measurement procedures. Urine albumin is an important biomarker for kidney damage. UA concentration is reported as a ratio to urine creatinine (UAC) to adjust for hydration influences. The diagnostic information obtained using the UAC is equivalent to the 24-hour urine albumin excretion rate.
There are currently no certified reference materials or reference measurement procedures for urine albumin. IVD manufacturers use either purified albumin from reagent suppliers or a diluted certified reference material for serum albumin for calibration of UA measurement procedures. A recent examination of commercially available measurement procedures showed that median values varied among methods by approximately 40 percent with greater differences at lower concentrations (Bachmann LM, et al. Clin Chem. 2014;60[3]:471–480). These differences are large enough to influence classification of disease using the recommended UAC threshold of 30 mg/g to identify kidney disease. There is justification for use of lower and different UAC thresholds for men versus women due to differences in urine creatinine. However, current measurement procedures do not have adequately standardized results for reliable measurements using lower UAC thresholds. Lack of suitable reference system components undoubtedly contributes to biases among measurement procedures.
The National Institute of Standards and Technology is developing new Standard Reference Materials for urine albumin and creatinine. A primary reference material of purified creatinine as well as a creatinine in human urine secondary reference material are now available. A primary reference material of purified albumin and an albumin in human urine secondary reference material are in preparation to provide higher order reference materials for standardization of UA measurement procedures.
Candidate reference measurement procedures based on isotope dilution tandem mass spectrometry of trypsin peptides from albumin in urine have been published by the Mayo Clinic renal reference laboratory (Lieske JC, et al. Clin Chem Lab Med. 2013;51[5]:981–989) and NIST (Beasley-Green A, et al. J Proteome Res. 2014;13[9]:3930–3939). These two candidate reference measurement procedures are currently being cross-validated and optimized to confirm their suitability for use as reference measurement procedures for urine albumin. We anticipate that certified reference materials and reference measurement procedures will be listed by the Joint Committee for Traceability in Laboratory Medicine (www.bit.ly/jctlm-crm) in the next few years that will enable standardization of commercially available urine albumin measurement procedures for use in clinical laboratories.
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Dr. Miller is a professor of pathology and Dr. Bachmann is an associate professor of pathology, Virginia Commonwealth University, Richmond. Dr. Miller is chair of the Laboratory Working Group of the National Kidney Disease Education Program, and Dr. Bachmann is chair of the IFCC Working Group for Standardization of Albumin in Urine.