Evaluation of strategy for testing thyroid function applied to hypothyroidism

Area of Science:

• Endocrinology
• Clinical Chemistry
• Diagnostic Medicine

Background:

• Thyroid function testing is crucial for diagnosing thyroid disorders.
• Primary hypothyroidism diagnosis often involves measuring thyroid stimulating hormone (TSH) and total plasma thyroxine (tT4).
• Evaluating the effectiveness of diagnostic strategies is essential for optimizing patient care and resource allocation.

Purpose of the Study:

• To retrospectively evaluate a thyroid function testing strategy involving discretionary thyroid stimulating hormone (TSH) assay after initial total plasma thyroxine (tT4) measurement.
• To assess the diagnostic yield of TSH testing in relation to primary hypothyroidism diagnosis.
• To compare TSH assay initiation by laboratory versus clinician/pathologist.

Main Methods:

• Retrospective analysis of 14,641 tT4 and 6,887 TSH assays over a two-year period.
• Categorization of TSH assays based on initiation source (laboratory, clinician, pathologist).
• Analysis of TSH values in relation to tT4 levels and clinical information.

Main Results:

• The percentage of elevated TSH values (over 5 mU/l) was comparable between laboratory-initiated (29%) and clinician/pathologist-initiated requests (23.2% and 23.6%).
• Among patients with tT4 below 100 nmol/l without TSH requests, 5.3% had elevated TSH values.
• A significant proportion of abnormal TSH results could be explained by unsubmitted clinical information.

Conclusions:

• The discretionary TSH testing strategy following tT4 measurement demonstrates similar diagnostic utility regardless of request initiation.
• The current strategy appears effective for identifying primary hypothyroidism.
• Improved communication of clinical information to the laboratory could further refine TSH assay interpretation.