endocrine and metabolic disorders
Hypothyroidism
Diagnosis of Hypothyroidism
Thyroid-stimulating hormone (TSH) Free thyroxine (T4) Thyroid-stimulating hormone (TSH) measurement is the most sensitive test for diagnosing hypothyroidism. In primary hypothyroidism, there is decreased feedback inhibition of the intact pituitary, and serum TSH is always elevated, whereas serum free T4 is low. In secondary hypothyroidism, free T4 and serum TSH are low (sometimes TSH is normal but with decreased bioactivity). Many patients with primary hypothyroidism have normal circulating levels of triiodothyronine (T3), probably caused by sustained TSH stimulation of the failing thyroid, resulting in preferential synthesis and secretion of biologically active T3. Therefore, serum T3 is not sensitive for hypothyroidism. Anemia is often present, usually normocytic-normochromic and of unknown etiology, but it may be hypochromic because of menorrhagia and sometimes macrocytic because of associated pernicious anemia or decreased absorption of folate. Anemia is rarely severe (hemoglobin is usually>9 g/dL [>90 g/L]). As the hypometabolic state is corrected, anemia subsides, sometimes requiring 6 to 9 months. Serum cholesterol is usually high in primary hypothyroidism but less so in secondary hypothyroidism. In addition to primary and secondary hypothyroidism, other conditions may cause decreased levels of total T4, such as Euthyroid Sick Syndrome and serum thyroxine-binding globulin (TBG) deficiency. 