Last Updated: 17-10-2019 11:29
Within the frame of the HBM4EU project, an EQUAS study was organised on the determination of 15 phthalate biomarkers in urine. This was the third ICI/EQUAS round for this substance group within the HBM4EU program.
In total 35 laboratories were invited for this third round, of which 24 laboratories registered. Results were received from 22 laboratories, located in 13 EU countries and the USA.
In May 2019, each participant received two burdened control materials of human urine, A and B (single tube each), containing phthalate biomarkers at various concentrations mostly in the range 1-2 µg/L and 5-30 µg/L, respectively.
Homogeneity assessment showed that both materials were sufficiently homogeneous for ICI/EQUAS testing. Previously conducted stability tests had shown that the biomarkers are stable when stored in the freezer and no significant loss of the biomarkers occurs during the course of the EQUAS test.
The proficiency of the laboratories was assessed through Z-scores calculated using the mean concentration as established by expert laboratories as assigned value, and a fixed fit-for-purpose relative target standard deviation (FFP-RSDR) of 25%. In two cases, the uncertainty of the expert values were too high, and the consensus value of participants and expert laboratories was used instead. Assigned values and Z-scores could be determined for 12 biomarkers in urine sample A and 14 biomarkers in urine B.
The percentage of satisfactory Z-scores obtained for each biomarker ranged from 75% for OH-MiNP in sample A, to 100% for 5OH-MEHP in sample A, and OH-MiDP and cx-MiDP in both samples. In most cases the satisfactory rate was 80-95%. One false positive and several false negatives were reported.
The number of phthalate biomarkers covered by the different laboratories varied widely: from 3 to all 15 target biomarkers. Seventeen labs covered ≥10 biomarkers. MEHP, 5OH-MEHP and 5oxo-MEHP were the most frequently determined phthalate biomarkers, followed by MEP, MBzP, MiBP, MnBP and 5cx-MEPP. cx-MiDP, MnPeP, MCHP, OH-MiNP, MnOP, and OH-MiDP were the least frequently determined biomarkers (included in the scope of 11-15 out of the 22 laboratories).
Compared to previous rounds, an improvement in laboratory performance was observed, indicating that the ICI/EQUAS exercises result in an overall improvement in the quality of phthalate biomarker analysis.