Thyroid function test assay interference: biochemical and clinical challenges and its implications

Smriti Acharya; Sharon Daniel; Suyash Acharya; Ramesh Chintavali Ajay; Rajinder Gupta; Daniel Kannappan

doi:10.1530/endoabs.110.EP1530

JOINT3205

Introduction: Thyroid hormone tests are widely used globally and play a crucial role in guiding treatment decisions and further diagnostic evaluations. Any inconsistency between clinical symptoms and test results must be thoroughly investigated to prevent misdiagnosis and unnecessary treatment. Automated thyroid tests can be affected by interferences, which may alter results and influence treatment decisions. These interferences can lead to incorrect treatments and changes in therapy. This review aims to explore the impact of assay interference on clinical management and highlights the importance of early detection to avoid inappropriate care.

Case report: Case 1: A 73 Y/F with post thyroidectomy for multinodular goiter on Thyroxine replacement was referred to the endocrinology clinic due to unusual thyroid function test (TFT) results (Table 1). Her clinical condition wasn’t corelating with TFT. Additional testing was performed at two separate laboratories using different methods, which confirmed interference. This helped avoid an unnecessary increase in her thyroxine dosage based on the initial abnormal results. Case 2: A 60 Y/F on thyroxine was referred for evaluation of persistent fatigue and tiredness. Her recent TFTs showed normal TSH but elevated FT4 levels, which did not match her clinical symptoms (Table 2). To clarify, repeat tests were done at two laboratories using different methods. The results confirmed a hypothyroid state, leading to an adjustment in her levothyroxine dose, which improved her symptoms.

Results: This table highlights the TFT variations across labs and reagents used.

Table 1. Case 1.
Lab	TSH (mIU/l)	T3(pmol/l)	T4(pmol/l)	Reagent
1.	2.8(0.35-5.50)	7 (3.5-6.5)	37.7 (10-20)	Siemens
2.	2.51(0.35-4.94)	N/A	12.5(9-19)	Rosche

Table 2. Case 2.
Lab	TSH (mIU/l)	T3(pmol/l)	T4(pmol/l)	Reagent
1.	8.3(0.35-5.50)	7.1(3.5-6.5)	22.2(10-20)	Siemens
2.	7.54(0.35-4.94))	6.51(2.4-6.1)	17.9(9-19)	Rosche

Discussion: Laboratory interference is a significant cause of misdiagnosis, so it’s important to always match test results with patient’s symptoms. Patients often have vague symptoms and when test results don’t match the clinical situation, interference should be suspected. A careful approach is needed, with collaboration between healthcare providers and lab experts to ensure accurate diagnosis and appropriate treatment.

Conclusion: According to the British Thyroid Association, TFT in the UK are requested around 10 million times annually, with an estimated cost of 30 million pounds. Collaboration between laboratory and clinical teams is essential for identifying potential interferences and ensuring that thyroid symptoms align with test results.

Endocrine Abstracts

EP1530