EXTENDED THYROID PROFILE (THYROID / HYPOTHYROIDISM TEST)

Thyroid Test

Thyroid function tests are a series of blood tests used to measure how well your thyroid gland is functioning. The thyroid produces 2 major hormones Triiodothyronine T3 and Thyroxine T4. Thyroid stimulating hormone TSH is a part of thyroid function test. It is a hormone secreted by pituitary gland, which releases certain hormones such as T3 (triodothyronine) and T4 (thyroxine) in the blood stream in response to thyroid hormone levels. It is secreted in larger amount if thyroid hormone levels are low and vice versa. TSH also exhibits circadian variations. Low levels are found during daytime and peaks are found during just after midnight.

The various functions of these hormones are-

• maintain body temperature
• regulate weight
• influence metabolism
• influence growth and brain development (during childhood)

Why is thyroid test prescribed?

Diagnose Hypothyroidism Thyroid hormone deficiency –

• Symptoms weight gain, lack of energy, depression, brittle hair & nails
• Causes- Hashimoto's thyroiditis, congenital hypothyroidism, Iodine deficiency etc

Hyperthyroidism Thyroid hormone excess

• Symptoms like weight loss, anxiety, tremors, diarrhoea etc
• Causes- Graves’ disease, Toxic adenoma, Toxic Multinodular goitre, Thyroiditis etc

Pregnancy has profound impact on thyroid gland and thyroid function. The gland increases 10-40% in size, along with approximately 50% increase in T3/T4 production and 50% increase in iodine requirements. In most normal Pregnancies, TSH levels are Lower than pre-pregnancy levels. This is more profound in twin pregnancies.

What are the components of thyroid test?

The various tests included in extended thyroid profile are-

• TSH-thyroid stimulating hormone
• Free T4 (thyroxine)
• Free T3 or total T3 (triiodothyronine)

Medications like steroids, aspirin, lithium, amiodarone and radio-iodine dye used in radiological procedures can interfere with Thyroid Function Test results.

The best way to avoid false fluctuations in lab test results is to have your thyroid levels checked under same conditions.

Reference range

T3, TOTAL	0.60- 1.81 ng/ml
T4, TOTAL	4.5-10.9 ug/dl
THYROID STIMULATING HORMONE (TSH)	0.55- 4.78 μlU/mL

Pregnancy (TSH)

1st trimester	0.10-2.50 μIU/ml
Pregnancy 2nd trimester	0.20-3.00 μIU/ml
Pregnancy 3rd trimester	0.30-3.00 μIU/ml
Pregnant Euthyroid Total T4 ug/dl	6.4-10.7 μg/dl

These values may vary from lab to lab.