Measurement of urine total sialic acid: comparison of an automated ultraviolet enzymatic method with a colorimetric assay

Abstract

An automated ultraviolet (UV) enzymatic assay for urine total sialic acid (SA), performed on a Cobas Fara analyser, is described and compared with the colorimetric Warren method, which is used widely to determine urine SA. Intra-assay coefficient of variation (CV) for urine total SA determination was 0.83% for the UV assay and 3.5% for the Warren method. Inter-assay CVs were 1.8% and 5.6%, respectively. Recovery of urine total SA ranged from 89% for the UV assay to 61% for the Warren method. Both were linear over a range of urine SA from 20 to 240 mg/L The UV assay was automated, took approximately 20 min to produce a result and avoided the need for solvent extraction; however, the reagents were expensive in comparison to those required for the Warren method. Urine samples with a creatinine concentration >14 mmol/L were diluted with distilled water to optimise SA recovery by the UV method. Urine SA:creatinine ratios for normals were 4.7 (±1.7) g/mol with the Warren method and 4.5 (±1.0) g/mol for the UV method. Similarly, in type-2 diabetic patients, urine SA:creatinine ratios were 7.6 (±2.3) g/mol (P<0.001) and 8.5 (±2.9) g/mol (P<0.001), respectively.

Keywords:

• Enzyme tests
• Sialic acids
• Urine analysis