Changes to Thyroid Hormone Testing – Provincial Harmonization
As of June 21, 2022, three key changes were made to thyroid testing across the province:
1. Updated pediatric and adult reference intervals for TSH, free T4 (fT4) and free T3 (fT3) (Table 1).
2. Updated progressive TSH algorithm (Figure 1).
3. Implementation of a standardized comment to automatically append to females of child-bearing age that includes a link for gestational age-specific reference intervals.
The above changes were made to promote provincial harmonization using a very large Alberta dataset. TSH, fT4 and fT3 results were analyzed provincially across multiple sites and with different assays. This confirmed assay comparability so that reference intervals and cutoffs could be aligned. Endocrinologists across the province were consulted in the process. In addition, the updated and optimized progressive TSH algorithm will now only reflex to fT4 when TSH is suppressed. This will improve laboratory follow-up testing, test utilization, and costs when screening and monitoring primary thyroid disease in the community, without compromising patient care. The availability of gestational age-specific reference intervals for thyroid tests across the province will assist in appropriate assessment and management of thyroid dysfunction in pregnancy.