There may be other features of hypopituitarism, such as menstrual cycle abnormalities and adrenal insufficiency. There might also be symptoms of a pituitary mass such as headaches and vision changes. Central hypothyroidism should be investigated further to determine the underlying cause. Overt
In overt primary hypothyroidism, TSH levels are high and T4 and T3 levels are low. Overt hypothyroidism may also be diagnosed in those who have a TSH on multiple occasions of greater than 5mIU/L, appropriate symptoms, and only a borderline low T4. It may also be diagnosed in those with a TSH of greater than 10mIU/L. Subclinical
Subclinical hypothyroidism is a milder form of hypothyroidism characterized by an elevated serum TSH level, but with a normal serum free thyroxine level. This milder form of hypothyroidism is most commonly caused by Hashimotos thyroiditis. In adults it is diagnosed when TSH levels are greater than 5 mIU/L and less than 10mIU/L. The presentation of subclinical hypothyroidism is variable and classic signs and symptoms of hypothyroidism may not be observed. Of people with subclinical hypothyroidism, a proportion will develop overt hypothyroidism each year. In those with detectable antibodies against thyroid peroxidase (TPO), this occurs in 4.3%, while in those with no detectable antibodies, this occurs in 2.6%. Those with subclinical hypothyroidism and detectable anti-TPO antibodies who do not require treatment should have repeat thyroid function tests more frequently (e.g. yearly) compared with those who do not have antibodies.
Encouraged by the World Health Organization, 70% of the worlds population across 130 countries are receiving iodized salt. In some countries, iodized salt is added to bread. Despite this, iodine deficiency has reappeared in some Western countries as a result of attempts to reduce salt intake.Pregnant and breastfeeding women, who require 66% more daily iodine than non-pregnant women, may still not be getting enough iodine. The World Health Organization recommends a daily intake of 250 µg for pregnant and breastfeeding women. As many women will not achieve this from dietary sources alone, the American Thyroid Association recommends a 150 µg daily supplement by mouth. Screening
Screening for hypothyroidism is performed in the newborn period in many countries, generally using TSH. This has led to the early identification of many cases and thus the prevention of developmental delay. It is the most widely used newborn screening test worldwide. While TSH-based screening will identify the most common causes, the addition of T4 testing is required to pick up the rarer central causes of neonatal hypothyroidism. If T4 determination is included in the screening done at birth, this will identify cases of congenital hypothyroidism of central origin in 1:16,000 to 1:160,000 children. Considering that these children usually have other pituitary hormone deficiencies, early identification of these cases may prevent complications.In adults, widespread screening of the general population is a matter of debate.