Rules-based detection of discrepancies between TSH and free T₄ results

Background: Analytical errors in clinical laboratory testing are unavoidable. Recent reports have suggested the idea of "physiological profiling" which uses several results from a given patient to identify clinically unlikely results. The objective of this study was to establish rules-based criteria for identifying physiologically unlikely TSH and free T₄ (fT₄) results. Methods: For a 30-month period, all samples with fT₄ concentrations >2 ng/dl and TSH concentrations >0.1 μIU/ml were investigated. Results: Among 7918 plasma samples for which both TSH and fT₄ concentrations were measured, 18 (0.23%) had fT₄ and TSH exceeding the investigated limits. Of these, two were due to heterophile antibody interference (with the TSH assay), one was proven to be due to random error, four could be explained by the patients' conditions, three were from infants <1 week of age, and the remaining eight were unresolved, primarily due to insufficient sample, discarded samples, and inability to obtain patient histories. Conclusions: This study defined a rules-based alert system for clinically unlikely combinations of TSH and fT₄ results. This pilot study demonstrates that this system is capable of detecting at least two different types of laboratory errors that would have otherwise gone undetected.