**7.2. Thyroid ultrasound**

170 Thyroid Hormone

thyrotoxicosis.

TSHR-Ab assay are:

thyrotoxicosis

Nodular variant of Graves' disease

**7.1. Radioactive iodine uptake (RAIU)** 

RAIU is diffusely increased.

**7. Laboratory diagnosis** 

Diagnosis of Graves' disease can be confirmed by measurement of serum TSH and total thyroxine (TT4) and triiodothyronine (TT3). Serum TSH level is suppressed or undetectable with increased TT4 and TT3 level in patients of Graves' disease. Serum TSH level is the most sensitive test. The free T4 (FT4) and free T3 (FT3) levels are increased more than that of TT4 and TT3. Measurement of FT4 and FT3 are expensive, and there is more chance of laboratory errors. FT4 and FT3 can be measured in conditions associated with high serum TBG level like pregnancy, oral contraceptive use and chronic liver disease. In patients of Graves' disease serum T3 level is proportionately more elevated than the serum T4 level. In upto 12% of patients, especially in the iodine deficient areas, only TT3 or FT3 is elevated with a normal TT4 or FT4 level, a condition known as T3 toxicosis. Conversely in some patients (iodine induced hyperthyroidism, drugs like amiodarone and propronolol which block the conversion of T4 to T3), only TT4 or FT4 is elevated with normal TT3 and FT3 (T4 toxicosis). Serum thyroglobulin level is high in all cases of thyrotoxicosis except factitious

Anti TPO antibody can be detected in upto 90%43,44 of patients with Graves' disease whereas anti-thyroglobulin antibody is present in 50-80% cases.45,46 They are useful in confirming the presence of thyroid autoimmunity but they are of limited diagnostic value. TSHR-Ab assay is very sensitive and specific (upto 98%) for the diagnosis of Graves' disease. But TSHR-Ab assay is quite expensive and not widely available. TSHR-Ab assay is indicated only when clinical and laboratory diagnosis are not clear. Indications for

Pregnant women with Graves' disease to predict the likelihood of neonatal

TSHR-Ab assay is also a useful indicator of the degree of disease activity. It can also predict the prognosis of Graves' disease. There is more chance of relapse in patients with

Associated hematological abnormalities include increased RBC mass, leucopenia with relative lymphocytosis, monocytosis and eosinophilia, increased factor VIII level. Other

RAIU is not required in each and every case of Graves' disease, but it is useful in excluding thyrotoxicosis caused by thyroiditis, factitious thyrotoxicosis, and type II amiodarone induces thyrotoxicosis. RAIU is absolutely contraindicated in pregnancy. In Graves' disease

Euthyroid Graves' disease, especially when it is unilateral

persistently high TSHR-Ab level after cessation of antithyroid drug.47

associated abnormalities include elevated liver enzymes, bilirubin and ferritin.

In Graves' disease thyroid tissue typically become hypoechoic because of reduction in colloid content, increase in thyroid vascularity and lymhocytic infiltration. In colour flow doppler there is a distinct pattern characterized by markedly increased signals, inferior thyroid artery and itrathyroidal artery velocities more than 40 cm/s. This pattern, in conjunction with a hypoechoic pattern allows distinction from Hashimoto's thyroiditis.
