Last Updated: 19-10-2020 15:58
Within the framework of the HBM4EU project, an interlaboratory comparison was organised and conducted for the analysis of arsenic in urine. Arsenic corresponds to 6 biomarkers: total arsenic, As(III), As(V), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA) and Arsenobetaine.
The study was performed in January 2020 and was conducted to assess the comparability and reliability of analytical methods across the participating expert laboratories.
The HBM4EU QAU had selected three expert laboratories for arsenic in urine. The expert laboratories were from three different countries in Europe.
The participation in this interlaboratory comparison for arsenic in urine was mandatory for these laboratories.
In January 2020, two different test samples consisting of 5 mL urine spiked with arsenic at two different concentrations (R1A, R1B) were prepared and sent to the participating expert laboratories for single analysis.
Homogeneity and stability assessment of the control materials confirmed that the materials were adequately homogeneous and stable.
Consensus values were calculated by averaging the values obtained by the expert labs when the relative uncertainty of the mean was within 17.5%.
In order to express the proficiency of the laboratories in a numerical way, Z-scores were calculated using the consensus value and a fixed fit-for-purpose relative target standard deviation (FFPRSDR) of 25%.
For total As, As (III)R1B, MMAR1B, DMA and Arsenobetaine, consensus values could be calculated from the results of all three experts, the obtained Z-scores were all satisfactory and the robust relative standard deviation (RSDR) was in a range from 1.4% to 27%.
In case there were only two results for a parameter, the two results were considered comparable when the difference to the mean was ≤35%. Then, no Z-scores were calculated.
For As (V)R1B no Z-score could be provided, because the relative uncertainty (u) of the mean concentration from three expert labs was too high and no statistical outlier could be detected. However, the results of two expert laboratories (AEL1 and AEL2) were in a good comparable range with a difference from the mean of 19.0%.
For As (III)R1A, As (V)R1A and MMAR1A, only two quantitative results were reported. These results showed a difference from the mean between 1.5% and 21.6% and were thus in a good comparable range.
The final evaluation about the comparability of the respective expert laboratories can however only be done after the completion of all interlaboratory comparison rounds.