Effect of storage time at −20°C on markers used for assessment of renal damage in children: albumin, γ-glutamyl transpeptidase, N-acetyl-β-d-glucosaminidase and α₁-microglobulin

Abstract

Objective. The objective of this study is to examine the influence of storage time at −20°C on the concentration of albumin, γ-glutamyl transpeptidase (γ-GT), N-acetyl-β-d-glucosaminidase (NAG), α₁-microglobulin (A1M) and creatinine in a large sample of healthy children. Material and methods. The New England Children's Amalgam Trial followed 534 children, aged 6–10 at baseline, for 5 years, with annual urine collections. Urine samples were analysed for creatinine, albumin, γ-GT, NAG and A1M concentrations. Repeated measures analysis of covariance was used to model the effect of storage time on these concentrations. Results. The γ-GT concentration decreased significantly with storage time at −20°C. There was also a limited decrease in NAG. Albumin, A1M and creatinine concentrations did not appear to be affected by storage time at −20°C. Conclusions. If it is necessary to interpret results from samples stored for a long time at −20°C, it is advisable to account for storage time in statistical models.

Key Words::

• A1M
• albumin
• children
• γ-GT
• NAG
• renal markers
• storage

Acknowledgements

We acknowledge Elsa Cernichiari for the laboratory analyses of creatinine and γ-GT. The study was by a cooperative agreement (U01 DE11886) between the New England Research Institutes and the National Institute of Dental and Craniofacial Research, National Institutes of Health, who also participated in the design and conduct of the study. Trial registration: clinicaltrials.gov; identifier NCT00065988.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.