Free triiodothyronine to free thyroxine ratio in the differential diagnosis of thyrotoxicosis and hyperthyroidism: A retrospective study

Evaluation of the prevalence and laboratory test results of overt thyrotoxicosis cases

BACKGROUND

The frequency of thyrotoxicosis may vary between countries and some laboratory test results may be used in etiology research. This study aimed to evaluate the prevalence of thyrotoxicosis diagnoses and laboratory test results.

METHODS

3246 patients with overt thyrotoxicosis were included in this study. Laboratory test results, epicrisis, thyroid ultrasonography, thyroid scintigraphy, and radioactive iodine uptake test reports of the patients were examined in the study.

RESULTS

Thyrotoxicosis was found due to levothyroxine overdose in 58.1% of the patients. When this group was excluded, 36.1% of the patients were diagnosed with toxic multinodular goiter most frequently. TRab levels were 8.5 times higher in Graves' disease than in other diagnostic groups. Anti-TPO levels were found to be the highest in the Graves' disease and Hashitoxicosis groups compared to other diagnostic groups (p<0.001). Anti-Tg levels were found to be highest in Graves' disease, Postpartum thyroiditis, and Hashitoxicosis patients (p<0.001). The free triiodothyronine / free thyroxine ratio was significantly higher, a cut-off value of >2.94 provided a sensitivity of 66% and specificity of 64% in diagnosing Graves' disease.

CONCLUSION

The causes of thyrotoxicosis show some differences between countries. Patients using levothyroxine should be informed about drug use and dose titration. The free triiodothyronine / free thyroxine ratio can be used in addition to other tests during diagnosis.

Indirect estimation of reference intervals for thyroid parameters using advia centaur XP analyzer

Background

The aim of this study was to determine the reference intervals (RIs) for thyroid stimulating hormone (TSH), free thyroxine (FT4), free triiodothyronine (FT3) and FT3/FT4 ratio using indirect methods.

Methods

We analyzed 1256 results TSH, FT4 and FT3 collected from a laboratory information system between 2017 and 2021. All measurements were performed on a Siemens ADVIA Centaur XP analyzer using the chemiluminescent immunoassay. We calculated the values of the 2.5th and 97.5th percentiles as recommended by the IFCC (CLSI C28-A3).

Results

The RIs derived for TSH, FT4, FT3 and FT3/FT4 ratio were 0.34-4.10 mIU/L, 11.3-20.6 pmol/L, 3.5-6.32 pmol/L and 0.21-0.47, respectively. We found a significant difference between calculated RIs for the TSH and FT4 and those recommended by the manufacturer. Also, FT3 values were significantly higher in the group younger than 30 years relative to the fourth decade (5.26 vs. 5.02, p=0.005), the fifth decade (5.26 vs. 4.94, p=0.001), the sixth decade (5.26 vs. 4.87, p<0.001), the seventh decade (5.26 vs. 4.79, p<0.001) and the group older than 70 years old (5.26 vs. 4.55, p<0.001). Likewise, we found for TSH values and FT3/FT4 ratio a significant difference (p <0.001) between different age groups.

Conclusions

The establishing RIs for the population of the Republic of Srpska were significantly differed from the recommended RIs by the manufacturer for TSH and FT4. Our results encourage other laboratories to develop their own RIs for thyroid parameters by applying CLSI recommendations.

Free triiodothyronine /free thyroxine ratio as an index of deiodinase type 1 and 2 activities negatively correlates with casual serum insulin levels in patients with type 2 diabetes mellitus

Free triiodothyronine/free thyroxine (FT3/FT4) ratio is considered as an index of the activities of iodothyronine deiodinase types 1 and 2 (DIO1 and DIO2, respectively) and is reportedly associated with insulin resistance in euthyroid adults. Euthyroid women with polycystic ovary syndrome accompanied with insulin resistance have lesser deiodinase activities. Correspondingly, the serum insulin level in a fasted condition positively correlates with the FT3/FT4 ratio, and insulin depletion decreases the DIO2 activity in mice. Selected genetic variants in DIO1 are also associated with insulin resistance measures. Therefore, if insulin positively regulates DIO1 and DIO2, the FT3/FT4 ratio should decrease under impaired insulin action, and the casual insulin level and FT3/FT4 ratio should be negatively correlated. To evaluate this hypothesis, we conducted a single-center retrospective study between 2018 and 2021. All participants visited the selected hospitals monthly for type 2 diabetes mellitus treatment and casual plasma glucose and HbA1c level measurements. Furthermore, their casual serum insulin levels were measured annually. Meanwhile, we excluded patients treated with insulin injection. Ultimately, we evaluated 71 patients, which all exhibited euthyroid conditions. The FT3/FT4 ratio was independently associated with thyroid-stimulating hormone, casual plasma glucose, and casual insulin levels. In terms of the regression coefficients of the univariate linear regression analysis, the FT3/FT4 ratio negatively correlated with the casual serum insulin levels. Therefore, the risk of FT3/FT4 ratio underestimation should be considered when diagnosing Graves' disease, which is often accompanied with insulin resistance.

Thyroid crisis caused by metastatic thyroid cancer: an autopsy case report

BACKGROUND

Thyroid crisis is a life-threatening condition in thyrotoxic patients. Although differentiated thyroid cancer is one of the causes of hyperthyroidism, reports on thyroid crisis caused by thyroid cancer are quite limited. Here, we describe a case of thyroid crisis caused by metastatic thyroid cancer.

CASE PRESENTATION

A 91-year-old woman was admitted to our hospital because of loss of appetite. Two years prior to this hospitalization, she presented with subclinical thyrotoxicosis and was diagnosed with histologically unidentified thyroid cancer with multiple metastases, and she refused aggressive medical interventions. On admission, she exhibited extreme thyrotoxicosis, and the presence of fever, severe tachycardia, impaired consciousness, and heart failure revealed the presence of thyroid crisis. All thyroid autoantibodies were negative. Multidisciplinary conservative treatment was initiated; however, she died on the fifth day after admission. Autopsy revealed the presence of primary anaplastic thyroid carcinoma and multiple metastatic foci arising from follicular thyroid carcinoma. Both primary and metastatic follicular thyroid carcinoma likely induced thyrotoxicosis, which could have been exacerbated by anaplastic thyroid carcinoma.

CONCLUSIONS

Even though the trigger of thyroid crisis in this patient is not clear, the aggravated progression of her clinical course suggests that careful monitoring of thyroid hormones and appropriate intervention are essential for patients with thyroid cancer.

New-onset thyrotoxicosis in a patient with anaplastic thyroid carcinoma: a diagnostic challenge

SUMMARY

Anaplastic thyroid cancer (ATC) is the type of thyroid cancer that has the worst prognosis. It usually presents as a rapidly growing cervical mass that generates compressive symptoms. Its association with thyrotoxicosis is rare. A 76-year-old woman, with no contributory history, presented with a 3-month course of fast-growing cervical tumor, associated with tenderness, cough, and weight loss. Physical examination revealed goiter, localized erythema, and a painful and stone tumor dependent on the right thyroid lobe. Due to the malignant findings of the thyroid ultrasound, the patient underwent a thyroid core needle biopsy, which indicated ATC. Laboratory tests revealed leukocytosis, decreased thyroid-stimulating hormone, elevated free thyroxine (fT4), and increased thyroperoxidase (TPO) antibodies. At the beginning, we considered that the etiology of thyrotoxicosis was secondary to subacute thyroiditis (SAT) after SARS-CoV-2 infection, due to the immunochromatography result and chest tomography findings. The result of markedly elevated TPO antibodies left this etiology more remote. Therefore, we suspected Graves' disease as an etiology; however, thyroid histopathology and ultrasound did not show compatible findings. Therefore, we suspect that the main etiology of thyrotoxicosis in the patient was the destruction of the thyroid follicles caused by a rapid invasion of malignant cells, which is responsible for the consequent release of preformed thyroid hormone. ATC is a rare endocrine neoplasm with high mortality; it may be associated with thyrotoxicosis, whose etiology can be varied; therefore, differential diagnosis is important for proper management.

LEARNING POINTS

Anaplastic thyroid cancer is the thyroid cancer with the worst prognosis and the highest mortality. The association of anaplastic thyroid cancer with thyrotoxicosis is rare, and a differential diagnosis is necessary to provide adequate treatment. Due to the current pandemic, in patients with thyrotoxicosis, it is important to rule out SARS-CoV-2 as an etiology. Anaplastic thyroid cancer, due to its aggressive behavior and rapid growth, can destroy thyroid follicular cells, generating preformed thyroid hormone release, being responsible for thyrotoxicosis.