LabMed

Secondary Amenorrhea Associated with Hypothyroidism

At a Glance

Approximately 1% of women of reproductive age experience secondary amenorrhea, cessation of menses. In women who previously experienced regular menstrual cycles, secondary amenorrhea is the absence of menstruation for 6 months. In women who had previously experienced irregular menstrual cycles, secondary amenorrhea is the absence of menstruation for 12 months. Secondary amenorrhea is a symptom caused by many pathological states, including pregnancy, polycystic ovary syndrome (PCOS), Cushing’s syndrome, hypopituitarism, hypothyroidism, and hyperprolactinemia. Some patients do not demonstrate an obvious etiology for their amenorrhea; however, the diagnostic evaluation should lead to the correct diagnosis if the problem is approached in a logical, stepwise manner.

What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?

In diagnosing the underlying cause of amenorrhea, the first step should always be to rule out pregnancy with a negative urine or serum hCG result. Next, levels of thyroid-stimulating hormone (TSH), prolactin, luteinizing hormone (LH), and follicle-stimulating hormone (FSH) should be ordered. If prolactin, LH, and FSH are normal, but TSH is elevated, then the amenorrhea is due to hypothyroidism.

Findings of elevated TSH are usually followed up by testing of free thyroxine (fT4) levels. High fT4 levels can indicate thyroid hormone resistance or a TSH-secreting adenoma of the pituitary. Low levels of fT4 can indicate primary hypothyroidism. Low or normal levels of fT4 should be followed up with thyroid autoantibody testing, which would confirm a diagnosis of Hashimoto's Disease.

Are There Any Factors That Might Affect the Lab Results? In particular, does your patient take any medications - OTC drugs or Herbals - that might affect the lab results?

Drugs that can affect TSH measurements include aspirin, prednisone, potassium iodine, lithium, dopamine, and amiodarone.

TSH, T4, and T3 are frequently measured by immunoassays. Different laboratories may use immunoassays utilizing different antibodies with differing specificities leading to discordant results. Additionally, patients may have circulating heterophilic antibodies, resulting in false-positive results in some serum assays.

What Lab Results Are Absolutely Confirmatory?

Elevated TSH levels are confirmatory of primary hypothyroidism; however, it does not indicate the underlying cause. Follow-up testing is usually necessary to determine cause and guide treatment.

Furthermore, suppressed TSH, although usually thought to indicate hyperthyroidism, can more rarely be an indication of secondary (pituitary) or tertiary (hypothalamus) hypothyroidism.

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