Abstract
A 59-year old female patient presented with apathy and 6 kg weight gain. Investigations revealed severe primary hypothyroidism (TSH>100 μIU/ml). L-thyroxine (L-T4) was started and titrated up to 75 μg, once daily, with clinical improvement. Other investigations revealed very high titres of anti-thyroid peroxidase (anti-TPO) and anti-thyroglobulin (anti-Tg) antibodies. After three months, there was a fall in TSH to 12.74 μIU/ml, however, with unexpectedly high free T4 (FT4) - 6.8 ng/ml and free T3 (FT3) - 6.7 pg/ml concentrations [reference range (rr): 0.8-1.9 ng/ml and 1.5-4.1 pg/ml (Siemens®), respectively]. At this stage L-T4 was stopped, and this was followed by a rapid increase in TSH (to 77.76 μIU/ml) and some decrease in FT4 and FT3, however FT4 concentration remained elevated (2.1 ng/ml). Following this, L-T4 was restarted. On admission to our Department, she was clinically euthyroid on L-T4, 88 μg, once daily. Investigations on Roche® platform confirmed mildly elevated TSH - 5.14 (rr: 0.27-4.2 μIU/ml) with high FT4 [4.59 (rr: 0.93-1.7 ng/ml)] and FT3 [4.98 (rr: 2.6-4.4 pg/ml)] concentrations. Other tests revealed hypoechogenic ultrasound pattern typical for Hashimoto thyroiditis. There was no discrepancy in calculated TSH value following TSH dilution (101% recovery). Concentrations of FT4 and FT3 were assessed on the day of discontinuation of L-T4 and after four days by the means of Abbott® Architect I 1000SR platform. These revealed FT4 and FT3 concentrations within the reference range [e.g., FT4 - 1.08 ng/ml (rr: 0.7-1.48)] vs 4.59 ng/ml (rr: 0.93-1.7, Roche®), FT3 - 3.70 pg/ml (rr: 1.71-3.71) vs 4.98 (rr: 2.6-4.4, Roche®)], confirming assay interference. Concentrations of ferritin and SHBG were normal.ConclusionsClinicians must be aware of possible assay interference, including the measurements of FT4 and FT3 in the differential diagnosis of abnormal results of thyroid function tests that do not fit the patient clinical presentation.
Highlights
A 59-year old female patient presented with apathy and 6 kg weight gain
Clinicians must be aware of possible assay interference, including the measurements of free T4 (FT4) and free T3 (FT3) in the differential diagnosis of abnormal results of thyroid function tests that do not fit the patient clinical presentation
Case presentation Written informed consent was obtained from the patient for publication of this case report and any accompanying images
Summary
Clinicians must be aware of possible assay interference, including the measurements of FT4 and FT3 in the differential diagnosis of abnormal results of thyroid function tests that do not fit the patient clinical presentation. 88 μg and free triiodotyronine (FT3) concentrations (SiemensW platform - see Table 1) At this stage L-T4 was stopped, this was followed by a rapid increase in TSH (to 77.76 μIU/ml) and some decrease in FT4 and FT3, FT4 concentration still remained elevated. There was a gradual decrease in TSH, with FT4 and FT3 concentrations above the reference range. Investigations performed in our Department (RocheW platform) confirmed mildly elevated TSH with high FT4 and FT3 concentrations (Table 2). Architect I 1000SR platform – Table 3) This revealed FT4 and FT3 concentrations within reference ranges. Following administration of a single dose of 300 μg, once daily, there a was a decrease in TSH with very little change of FT4 and FT3 (RocheW platform). The patient, as well as her GP were informed about problems with FT4 and FT3 measurements, and that further adjustments of L-T4 dose should be based on clinical picture, as well as TSH measurements alone
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