Elevated free T4 levels, exceeding the normal reference range (e.g., an upper limit like 1.7 ng/dl), can indicate an overactive thyroid gland (hyperthyroidism), thyroiditis, or toxic thyroid conditions. High free T4 can also point to thyrotoxicosis. This condition, characterized by various symptoms and an overactive thyroid gland, is also known as 'toxic goiter'.