Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (761 page)

   Acute or chronic thyroiditis

   Chronic renal failure

Decreased Values

   Following surgical therapy for MTC

   In cases of complete cures, serum calcitonin levels fall into the undetectable range over a variable period of several weeks.

   A rise in previously undetectable or very low postoperative serum calcitonin levels is highly suggestive of disease recurrence or spread and should trigger further diagnostic evaluations.

   Limitations

   Basal fasting level may be increased in patients with MTC, even when there is no palpable mass in the thyroid.

   Values follow a circadian pattern, with a peak after lunchtime.

   Basal level is normal in approximately one third of cases of MTC.

   Levels of >2,000 pg/mL are almost always associated with MTC, with rare cases due to obvious renal failure or ectopic production of calcitonin.

   Levels of 500–2,000 pg/mL generally indicate medullary carcinoma, renal failure, or ectopic production of calcitonin.

   Levels of 100–500 pg/mL should be interpreted cautiously with repeat assays and provocative tests. If repeat tests in 1–2 months are still abnormal, some authors recommend total thyroidectomy.

   This test is not useful for evaluating calcium metabolic diseases.