Last Updated: 17-10-2019 11:12
Within the frame of the HBM4EU project, an EQUAS study was organised on the determination of 15 phthalate biomarkers in urine. This was the second ICI/EQUAS round for this substance group within the HBM4EU program.
In total 35 laboratories were invited for this second round, of which 25 laboratories registered.
Results were received from 24 laboratories, located in 16 EU countries and the USA.
In December 2018, 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 0.5-10 µg/L and 10-50 µg/L, respectively.
Homogeneity assessment showed that both materials were sufficiently homogeneous for ICI/EQUAS testing. The stability test demonstrated no significant loss of the biomarkers 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%. Assigned values and Z-scores could be determined for 13 biomarkers in urine sample A and all 15 biomarkers in urine B.
The percentage of satisfactory Z-scores obtained for each biomarker ranged from 100% for 5OHMEHP (4.1 ng/ml), to 52% for MEHP in sample A (0.57 ng/ml), and was around 80% in most other cases with cx-MiNP and OH-MiDP as the other exceptions. 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. Eighteen labs covered ≥10 biomarkers. MEHP, 5OH-MEHP and 5oxo-MEHP were the most frequently determined phthalate biomarkers, followed by MEP, MBzP, MiP, 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 10-14 out of the 24 laboratories).