Labs: Endocrine

Mention a biologically inactive form of thyroid hormone.

(reverse T3 [rT3])

Mention different carrier proteins for T3 and T4.

1. Thyroxine-binding globulin (TBG)

2. Thyroxine binding prealbumin (transthyretin)

3. Albumin

Mention screening for neonatal hypothyroidism, and mention most common defect.

Nationwide screening programs including T4 and TSH assays on filter- paper disk are now available

Incomplete development of the thyroid is the most common defect

Mention features of non-thyroidal illness.

• Patients typically present with low serum T3 and high levels of rT3.

• Total T4 and FT4 will progressively diminish.

• These findings mimic those of hypothyroidism and

  are often called euthyroid sick syndrome.

• TSH is usually normal but may be undetectable in

  severely ill patients.

• During recovery, TSH may rise transiently into the hypothyroid range as thyroid hormone concentrations return to normal.

Mention thyroid hormone resistance features and a similar condition to it and how to differentiate.

• Patients are clinically euthyroid because of compensatory increases in plasma thyroid hormoneconcentrations driven by a small increase in TSH secretion.

• This combination of raised free thyroid hormone and TSH concentrations is also seen in patients with rare TSH-secreting pituitary adenomas, but in contrast, the latter are clinically thyrotoxic.

Mention thyroid and pituitary response to treatment, and mention suitable marker to evaluate treatment for thyroid.

• Thyroid hormones respond within a few days to different types of treatment.

• Pituitary is slow to register acute changes in thyroid hormone status: this is called pituitary lag.

• TSH is not suitable to evaluate recent treatment.

• Serum FT4 measurement is a more reliable indicator.

Mention duration needed for TSH to reach steady state following treatment of hypo and hyperthyroidism.

• 4 – 8 weeks for TSH to reach a new steady state following treatment of hypothyroidism and 8 – 16 weeks in hyperthyroidism.

Mention normal Ca level.

(8.5 – 10.5 mg/dL)

What is pseudohypoparathyroidism and mention its presentation?

• It is a rare hereditary disorder characterized by end organ resistance to PTH despite elevated hormone levels.

• Parathyroid gland is intact but kidney and bones fail to response appropriately leading to Hypocalcemia and Hyperphosphatemia.

• Some presents with Albright’s hereditary Osteodystrophy (short stature, round face and brachydactyly) while others have only biochemical abnormalities