Original Investigation
Pathogenesis and Treatment of Kidney Disease and Hypertension
Population Prevalence of Albuminuria in the Australian Diabetes, Obesity, and Lifestyle (AusDiab) Study: Immunonephelometry Compared With High-Performance Liquid Chromatography

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Background: Microalbuminuria is an independent risk factor for cardiovascular morbidity and mortality in the general population. Standard immunochemical urinary albumin assays detect immunoreactive albumin, whereas high-performance liquid chromatography (HPLC) detects both immunoreactive and immunounreactive albumin. Methods: Using data from the Australian Diabetes, Obesity, and Lifestyle cohort study of randomly selected community-based Australian adults, spot urine samples were tested for albuminuria (spot urine albumin-creatinine ratio [ACR]: normal, <30 mg/g; microalbuminuria, 30 to 300 mg/g; and macroalbuminuria, >300 mg/g) by using both immunonephelometry (IN) and HPLC (n = 10,010). Results: Bland-Altman analysis showed significant bias, with a greater ACR by means of HPLC, particularly at lower levels of ACR. Mean ACR was 15.8 mg/g (95% confidence interval [CI], 12.3 to 19.2) by means of IN compared with 30.0 mg/g (95% CI, 27.0 to 35.0) by means of HPLC. The prevalence of microalbuminuria was 4 times greater by means of HPLC compared with IN (20% versus 5.5%). In all demographic and comorbid subgroups associated with microalbuminuria, the prevalence of microalbuminuria increased by 2 to 4 times. A total of 1,743 subjects (17.4%) classified as normoalbuminuric by means of IN were reclassified as microalbuminuric by means of HPLC. Using multivariate logistic regression, women, patients with untreated and treated hypertension, and those with impaired glucose tolerance or diabetes were associated significantly with a change in category from normoalbuminuric to microalbuminuria by means of HPLC. Conclusion: HPLC measures significantly more urinary albumin within the normoalbuminuria and microalbuminuria range, resulting in a significant increase in prevalence of microalbuminuria. Longitudinal studies are needed to determine whether the extra individuals identified by means of HPLC are at increased risk for developing hard clinical outcomes (renal and cardiovascular).

Section snippets

Study Design and Population

This study uses data from the AusDiab Study.17 The AusDiab Study was a nationwide population-based survey undertaken between May 1999 and December 2000 to determine the prevalence of diabetes mellitus, obesity, and cardiovascular disease risk factors. Indicators of kidney disease and assessment of kidney function also were assessed.18

The population, methods, and response rates have been described in detail elsewhere.17 In brief, the target population of noninstitutionalized adults 25 years and

Results

Table 1 lists characteristics of the adult population estimated from the AusDiab cohort assessed in this study. A quarter of the adult population was hypertensive, the majority of whom were not administered antihypertensive medication. Likewise, the prevalence of an abnormality in glucose metabolism was just less than 25%; a total of 7.2% had diabetes and half of these were not known to have diabetes before the study. Mean urine ACR was 15.8 mg/g (95% confidence interval [CI], 12.3 to 19.2) by

Discussion

This study shows important clinical findings associated with the estimation of urinary albumin by means of HPLC. We show that the increase in quantity of albumin detected in urine (in this case, measured by using urine ACR) determined by means of HPLC compared with the traditional immunoassays previously reported in patients with diabetes (n = 97)12 and a selected population with a high prevalence of microalbuminuria from the PREVEND study (n = 1,312)16 also is present in a large representative

Acknowledgment

The authors thank the participants, the AusDiab Survey Team and Steering Committee, and AusAm Biotechnologies Inc (New York), for supplying the equipment and reagents for the measurement of urinary albumin by means of HPLC.

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    Support: AusAm Biotechnologies, Inc (New York), supplied the equipment and reagents for the measurement of urinary albumin by HPLC. (AusAm Biotechnologies, Inc [New York], took no part in the study design, data analysis, interpretation, or writing of the manuscript.) The AusDiab Study was supported by the Commonwealth Department of Health and Aged Care, State Governments of Queensland, South Australia, Tasmania, Western Australia and Victoria and Territory Health Services, the Australian Kidney Foundation, Diabetes Australia (Northern Territory), the International Diabetes Institute, Eli Lilly (Australia), Janssen-Cilag (Australia), Abbott (formally Knoll) Australia, Merck Lipha s.a. Alphapharm, Merck Sharp & Dohme (Australia), Pharmacia and Upjohn, Roche Diagnostics, Glaxo SmithKline, BioRad Laboratories, HITECH Pathology, and Qantas Airways. Potential conflicts of interest: P.Z.Z. and R.C.A. are members of the scientific advisory board committee to AusAm Biotechnologies, Inc. No financial fees are paid to them by AusAm Biotechnologies, Inc.

    Originally published online as doi:10.1053/j.ajkd.2005.12.034 on February 24, 2006.

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