A particle-enhanced turbidimetric immunoassay for quantitative determination of orosomucoid in urine: development, validation and reference values.

Increased urinary orosomucoid excretion rate (UOER) is an independent predictor of cardiovascular and all-cause mortality in patients with type 2 diabetes, as demonstrated by a conventional, immunoturbidimetric method. We wanted to optimize the method by developing a fully automated, particle-enhanced turbidimetric (PET) immunoassay with a lower detection limit, to allow assessment of orosomucoid in urine in healthy individuals and patients. A micro-particle-based immunoreagent was prepared for a PET immunoassay. The calibration was traceable to the certified reference material (CRM 470) for specific human serum proteins. We studied 69 healthy adults (28 men and 41 women) to establish reference values for the new assay. The detection limit of orosomucoid in urine was found to be 0.05 mg/l, about 20 times lower than for the conventional assay. Within-run imprecision [CV%, (level)] was 6.7% (0.23 mg/l), 1.0% (1.08 mg/l) and 1.0% (4.69 mg/l). Total imprecision [CV%, (level)] was 10.4% (0.23 mg/l), 3.9% (1.08 mg/l) and 3.4% (4.69 mg/l). Reference values [median (2.5-97.5 percentiles)] for UOER were 0.36 (0.07-2.04) microg/min and for urinary orosomucoid/creatinine ratio 0.04 (0.009-0.17) mg/mmol. We describe a fully automated, transferable, sufficiently precise, high-sensitivity assay for orosomucoid in urine and present reference values traceable to CRM 470.

Orosomucoid in urine predicts cardiovascular and over-all mortality in patients with Type II diabetes.

AIMS/HYPOTHESIS: Urinary orosomucoid excretion rate is increased in a substantial proportion of patients with Type II (non-insulin-dependent) diabetes mellitus and normal urinary albumin excretion rate. The aim of this study was to determine whether increased urinary orosomucoid excretion rate is predictive of increased mortality in patients with Type II diabetes. METHODS: In a cohort study including 430 patients with Type II diabetes, baseline urinary samples were analysed for orosomucoid and albumin. Mean follow-up was 2.4 years. RESULTS: We found that 188 (44 %) patients had normal and 242 (56 %) patients had increased urinary orosomucoid excretion rates. During the study period 41 patients died; out of these 23 patients died of cardiovascular diseases. Odds ratio for all-cause mortality was 2.50 (95 % CI 1.00-6.22) and odds ratio for cardiovascular mortality was 9.81 (1.31-73.6) having increased urinary orosomucoid excretion rate at baseline (odds ratios adjusted for age, sex, duration of diabetes, cardiovascular diseases, weight, medication, HbA1 c, plasma creatinine and urinary albumin excretion rate). Urinary albumin excretion rate was an independent predictor of all-cause mortality when urinary orosomucoid excretion rate was not included in the analysis. Subgroup analysis revealed that 39 % of the patients with normal urinary albumin excretion rate (n = 251) had increased urinary orosomucoid excretion rates and that these patients had a higher cardiovascular mortality (p = 0.007) than patients with normal urinary albumin excretion rate and normal urinary orosomucoid excretion rates. CONCLUSION/INTERPRETATION: We found that urinary orosomucoid excretion rate predicted all-cause and cardiovascular mortality in patients with Type II diabetes independently from other risk factors.