Calculation of continuous reference intervals for biological parameters exhibiting strong age-dependent level changes: Its application to glycosaminoglycans and sialic acid in urine.

Glycosaminoglycan (GAG) and sialic acid (total and free) assays are used as first-line screening tests for the diagnosis of mucopolysaccharidoses and glycoproteinoses, respectively. There is a pronounced age-dependent variation in the urinary concentrations of these metabolites in the normal population, and the stratification of the reference values into discrete age ranges may lead to an undesirably high number of false-positive or false-negative results. The aim of this study was to design a method for calculating continuous reference intervals as a function of age and its application to the analysis of GAGs and sialic acid (total, free, and conjugated) in urine.

New method for the determination of the net bilirubin absorbance in cerebrospinal fluid that minimizes the interference of oxyhaemoglobin and biliverdin.

The presence of oxyhaemoglobin and biliverdin interferes with the method recommended by the UK NEQAS Specialist Advisory group for EQA of CSF Proteins and Biochemistry for estimating of the net bilirubin absorbance in CSF. This is easily demonstrated by using solutions with different concentrations of these three substances.The two secondary peaks of the oxyhaemoglobin spectrum at 540 nm and 577 nm are used as reference to minimize these interferences.