Predictive Value of Nephelometric and High-Performance Liquid Chromatography Assays of Urine Albumin for Mortality in a High-Risk Aboriginal Population
Received 11 October 2007; received in revised form 6 March 2008 published online 01 July 2008.
Background
Urine albumin assays by high-performance liquid chromatography (HPLC) yield greater values than immunoassays at lower albumin levels. We compared predictive values of albumin-creatinine ratios (ACRs) by these 2 techniques for mortality in Aboriginal people.
Study Design & Setting
This was a longitudinal study of 741 adults in a remote Aboriginal community who participated in a baseline health survey between 1992 and 1998 at ages ranging from 18 to 84 years (mean, 34 years). All natural deaths were documented on follow-up until 2006. Urine albumin concentrations were measured simultaneously by using both nephelometric and HPLC techniques on baseline urine samples retrieved from −70°C storage, as well as creatinine concentrations, and ACRs were derived. Age- and sex-specific tertiles of ACR were compiled. Cox regression analyses were used to evaluate the predictive value of ACR for natural deaths by ACR tertiles and again by z score changes in ACRs as continuous variables.
Results
Participants were followed up for a median of 11 years, during which a total of 119 natural deaths were documented. ACRs on baseline urine samples were greater by HPLC than immunoassay at lower ACR ranges, but were fairly concordant at levels greater than 100 mg/mmol. Levels of ACR by both techniques were strong predictors of death, but correlations of death with ACR tertiles and with ACR levels on a continuum were similar for the 2 techniques.
Limitations
The age- and sex-specific tertiles used might introduce some risk of bias in the assessment of predictive value. In addition, assays were performed on urine after more than 10 years of cold storage.
Conclusion
Despite different absolute values, this study did not show that ACR level by either technique was superior in predicting deaths.
1Centre for Chronic Disease, School of Medicine, The University of Queensland, Brisbane
2Department of Nephrology, Monash Medical Centre, Monash University, Melbourne, Australia
Address correspondence to Wendy E. Hoy, FRACP, Centre for Chronic Disease, School of Medicine, The University of Queensland, Royal Brisbane & Women's Hospital, Herston QLD 4029, Australia
The field work to gather the baseline data was done while Dr Hoy was based at the Menzies School of Health Research, Darwin, NT, Australia.
ABSTRACT