Articles on Medical Diseases and Conditions

Entries for the ‘Thyroid Function Tests’ Category

Neonatal Hypothyroid Screening

Congenital hypothyroidism occurs in approximately 1 in 6,000 infants (literature range, 1-3/10,000), which makes it about 3 times as common as phenylketonuria (PKU). Approximately 85% of cases are due to thyroid agenesis and 10% are defects of enzymes in thyroid hormone synthesis, so that about 95% of all cases are primary hypothyroidism and 3%-5% are […]


The usual classification of thyroiditis includes acute thyroiditis, subacute thyroiditis, chronic thyroiditis, and Riedel’s struma. Acute thyroiditis is generally defined as acute bacterial infection of the thyroid. Signs, symptoms, and laboratory data are those of acute localized infection. Riedel’s struma consists of thyroid parenchymal replacement by dense connective tissue. In some cases at least this […]

Monitoring of Replacement Therapy

Desiccated thyroid and presumably other T4 and T3 combinations result in T3-RIA values that may become elevated for several hours after administration and then decrease into the reference range. T4 values remain within the reference range if replacement is adequate. In the few instances when clinical evidence and T4 results disagree, TSH assay is helpful. […]

Comments Regarding Use of Thyroid Tests

As previously noted, some thyroidologists and laboratorians advocate screening for thyroid disease with a single test, often citing need for cost containment. The ultra sensitive TSH appears to be advantageous for this purpose. The T4 test result is more frequently normal in mild disease and more frequently abnormal in the absence of thyroid disease than […]

Summary of Laboratory Tests in Hypothyroidism

From the preceding discussion, several conclusions seem warranted: 1. Serum T4 is the most widely used screening test for hypothyroidism, but some physicians use FT4 or serum TSH assay instead. Values in the upper half of the T4 and FT4 reference range are strong evidence against hypothyroidism unless the TBG level is increased (congenital, pregnancy, […]

False Laboratory Euthyroidism in Hypothyroid Patients

Normal T4 values in a hypothyroid patient may occur in the following conditions: 1. In early or very mild hypothyroidism. Serum TSH values are usually elevated. Some investigators have reported patients in whom the T4 and TSH values were both within reference range, but the TRH test result exhibited an exaggerated response suggestive of hypothyroidism. […]


Pseudo hypothyroidism may be defined as a deceased T4 level in a euthyroid person. This may occur with (1) decreased TBG or TBG binding (congenital or drug induced), (2) certain medications (e.g., phenytoin, lithium, dopamine, corticosteroid), (3) some patients with severe non thyroidal illness, (4) some clinically euthyroid patients with Hashimoto’s thyroiditis, (5) after recent […]

Thyroid Tests in Hypothyroidism

Serum thyroxine. Thyroxine is frequently used as the major screening test for hypothyroidism, since the T4 level is low in most cases. There is some overlap between hypothyroid patients and normal persons in the lower part of the T4 reference range, since persons with mild, early, or subclinical disease may be inadvertently included in groups […]

Laboratory Test Patterns in Hypothyroidism

The physiology of thyroid hormone production in hypothyroidism is similar to that described in hyperthyroidism. Hypothyroidism may be divided into three types, depending on functional defect. Each of these categories may have various etiologies: (1) primary (primary thyroid T4/T3 secretion defect), (2) secondary (pituitary TSH secretion defect), and (3) tertiary (hypothalamus TRH secretion defect). From […]

Confirmatory Tests for Hyperthyroidism

The existence of deceptive laboratory hyperthyroidism with the various forms of pseudo toxicosis accentuates the need for reliable confirmatory tests. This is especially true when the patient has severe non thyroidal illness and symptoms such as atrial fibrillation that may be due to thyrotoxicosis. At present, the two most useful confirmatory procedures for hyperthyroidism are […]