What does a decrease in T3 and T4 levels indicate?

A decrease in T3 and T4 levels is indicative of hypothyroidism. This condition occurs when the thyroid gland is underactive and fails to produce enough of the hormones triiodothyronine (T3) and thyroxine (T4), which are essential for regulating metabolism, energy levels, and overall growth and development.

In hypothyroidism, the low levels of these hormones can lead to various symptoms such as fatigue, weight gain, depression, and sensitivity to cold, among others. The body's metabolism slows down due to the insufficient levels of thyroid hormones, ultimately affecting multiple systems in the body.

The other options represent different conditions: hyperthyroidism involves an overproduction of T3 and T4, normal thyroid function would show normal levels of these hormones, and thyroid cancer might not specifically correlate with decreased hormone levels as patients may still produce normal or elevated levels of T3 and T4 despite having cancer.