Differential Diagnosis for TSH <0.010, Free T4 2.56, Free T3 7.64

• Single Most Likely Diagnosis

  • Hyperthyroidism (Primary): This is the most likely diagnosis given the suppressed TSH level (<0.010) and elevated free T4 and free T3 levels. Hyperthyroidism is characterized by an overproduction of thyroid hormones, which can be due to several causes including Graves' disease, toxic multinodular goiter, or solitary toxic nodule.

• Other Likely Diagnoses

  • Thyroiditis: This condition involves inflammation of the thyroid gland, which can lead to the release of stored thyroid hormones into the bloodstream, causing temporary hyperthyroidism. The TSH level is low due to feedback inhibition from the high levels of circulating thyroid hormones.
  • Exogenous Thyroid Hormone Ingestion: Intentional or accidental ingestion of thyroid hormone medication can suppress TSH production and elevate free T4 and free T3 levels, mimicking hyperthyroidism.
  • Pituitary or Hypothalamic Disease: Certain conditions affecting the pituitary or hypothalamus can lead to alterations in TSH secretion, although these would more commonly present with other hormonal imbalances.

• Do Not Miss Diagnoses

  • Thyroid Storm: A life-threatening complication of untreated or inadequately treated hyperthyroidism. Although the laboratory values alone do not diagnose thyroid storm, the clinical presentation (e.g., severe tachycardia, fever, agitation) is critical for diagnosis.
  • Malignancy: Rarely, certain types of cancer (e.g., metastatic follicular thyroid cancer) can produce thyroid hormones, leading to hyperthyroidism. This diagnosis is crucial to identify due to its implications for treatment and prognosis.

• Rare Diagnoses

  • TSH-Producing Pituitary Adenoma: A rare type of pituitary tumor that secretes TSH, leading to hyperthyroidism. However, this condition would typically present with elevated TSH levels, not suppressed.
  • Struma Ovarii: A rare ovarian tumor that contains thyroid tissue and can produce thyroid hormones, leading to hyperthyroidism. This condition is extremely rare and usually presents with a pelvic mass.
  • Familial Dysalbuminemic Hyperthyroxinemia: A rare genetic condition characterized by abnormal binding of T4 to albumin, leading to elevated free T4 levels but normal TSH and free T3 levels. However, the free T3 level is elevated in this case, making this diagnosis less likely.