Reference intervals for thyroid markers in early pregnancy determined by 7 different analytical systems

Area of Science:

• Endocrinology
• Clinical Chemistry
• Reproductive Medicine

Background:

• Accurate thyroid function testing is crucial during pregnancy.
• Established reference intervals for thyroid hormones and antibodies can vary between laboratory methods.
• Understanding these variations is key for appropriate clinical interpretation.

Purpose of the Study:

• To determine reference intervals for TSH, FT4, and TPO Ab in pregnant women.
• To compare these intervals with manufacturer-provided ranges for healthy populations.
• To investigate inter-system variability in thyroid function test results.

Main Methods:

• Thyroid function tests (TSH, FT4, TPO Ab) were analyzed in 216 pregnant women without thyroid history.
• Reference intervals were established using seven different global analytical immunoassay systems.
• Data were compared against manufacturer-specific reference ranges.

Main Results:

• FT4 reference intervals showed slight variations, with UniCel DxI yielding the lowest range (8.13-13.2 pmol/L).
• TSH intervals differed, with Modular E170 and IRMA Immunotech recommending higher ranges (0.25-3.86 mU/L) and Immulite 2500/AIA 2000 lower ranges (0.17-2.81 mU/L).
• TPO Ab cut-off limits varied by system but were generally consistent with manufacturer recommendations.

Conclusions:

• Significant inter-system variability exists for TSH and FT4 reference intervals in pregnant women.
• Current analytical systems provide differing reference ranges, necessitating careful interpretation.
• TPO Ab cut-offs are system-dependent but align with manufacturer guidelines.