Reference intervals for thyroid hormones on Advia Centaur derived from three reference populations and a review of the literature

Introduction: Laboratories are recommended to determine their own local reference intervals (RIs) to embrace the variations in local populations. We have assessed local RIs for thyroid function tests using two different approaches to selection of reference populations and also searched the literature for studies using the Advia Centaur methods.

Methods: Two independent populations were made of redundant serum samples from primary care in which exclusion criteria were used to reduce the inclusion of patients with thyroid disease. A further population of healthy subjects were recruited. All groups were restricted to 18-65 years and thyroid peroxidase antibodies (TPOabs) positive subjects were excluded. All samples were analysed using Advia Centaur reagents. A literature search was made for RI studies on non-pregnant adults using Advia Centaur.

Results: Redundant data sets consisted of 219 and 222 subjects and a healthy population of 280. Comparison of variance of all three groups showed differences for free T4 (fT4) and total T3 (TT3) (analysis of variance P < 0.0001) but thyroid-stimulating hormone (TSH) was similar across all three groups (P = 0.7656). RI for TSH, fT4 and TT3 all fell within the 95% confidence interval for each other for all three analytes. Published RIs give wide variation although their mean is similar to the prospective data reported here.

Discussion: Our data suggest that a consensus set of RIs for Advia Centaur can be adopted from the prospective studies and literature search in this paper and we would suggest the following RIs: TSH 0.5-4.4 mIU/L; fT4 10-20 pmol/L; and TT3 1.1-2.4 nmol/L.