Pre-mixing serum samples with assay buffer is a prerequisite for reproducible anti-Mullerian hormone measurement using the Beckman Coulter Gen II assay

Study question: Does pre-mixing stored serum samples with assay buffer improve the reproducibility of the Beckman Gen II assay for anti-Müllerian hormone (AMH)?

Summary answer: Pre-mixing serum samples with assay buffer is a prerequisite for reproducible measurement of AMH in serum using the Beckman Coulter Gen II assay.

What is known already: Discrepancies in the results obtained from AMH assays have raised doubts concerning the clinical utility of measuring AMH. Sample storage conditions may be responsible for the lack of reproducibility of results obtained from the Gen II kit.

Study design, size, duration: This was a prospective study in which serum samples were stored at three different temperatures and assayed for AMH at times 0, 4, 8, 12, 24, 48 h and 1 or 2 weeks after collection. Volunteers (n = 28) were healthy non-pregnant and early pregnant women aged 22-41 years. Anonymized long-term stored samples (n = 42, stored at -20° for 2 weeks) from fertility clinic attendees were also included. For determining the reference range, 179 samples from healthy pregnant women presenting for first trimester screening were used.

Participants/materials, setting, methods: Thirty separate assays were performed by two operators using four different Gen II kit lots with both kit and in-house quality controls (QCs) included in each assay. In addition to the standard protocol, a modified protocol (pre-mixing samples with assay buffer) was used for selected sample groups.

Main results and the role of chance: In non-pregnant women, AMH concentrations remained unchanged in serum stored for up to 8 h at room temperature, -20 and -80°C. At room temperature, levels started to rise by 24 h, increasing by up to 29% of the time 0 h value by 48 h and 26% after 1 week. Significant changes versus baseline (time 0 h) in measured AMH concentration were also observed after storage at -20 and -80°C (only at the 12 h time point). In the pregnant group, there was a 50% increase above baseline in samples stored for 48 h at room temperature. When samples were pre-mixed with assay buffer, AMH concentrations showed a consistent increase versus the standard assay in both non-pregnant (29%) and pregnant (280%) groups, regardless of storage conditions and duration, but concentrations remained constant during long-term storage (2 weeks). Stored fertility clinic patient samples also exhibited stability of AMH values after a consistent 2-fold increase following pre-mixing. Kit QCs were consistent over 30 weeks using either standard or modified protocols while the in-house pooled serum QC rose over time unless using the modified protocol. Overall, there was a 2-fold increase in medians in the pre-mixed reference range, with the biggest increase observed in the oldest age bracket (41-45 years, 3.4-fold).

Limitations, reasons for caution: The cause of the observed instability of AMH in stored serum samples requires further investigation, which is outside the scope of this publication. A larger and wider population study is necessary for a more reliable and clinically relevant reference range.

Wider implications of the findings: Our study has confirmed previous findings of lack of consistency in AMH concentrations when measured with the Gen II assay. Pre-mixing serum samples with assay buffer gave higher but also the most consistent results regardless of storage conditions; therefore, we propose that all serum samples for AMH assay should be pre-mixed with assay buffer. Furthermore, clinical laboratories that offer AMH measurement as part of the assessment of endocrinopathies, such as polycystic ovary syndrome or premature ovarian failure, or for management of ovulation induction as part of assisted reproduction, must re-establish their own normal ranges using the modified method.

Study funding/competing interest(s): No funding was obtained for this study. There are no conflicts of interest to declare.