In a child presenting with gigantism, what lab value should be checked first?

• A. Growth hormone
• B. Insulin-like growth factor 1 (IGF-1)
• C. Prolactin
• D. Thyroid function tests

Answer: (B)

In evaluating a child with gigantism, the first lab value to check is Insulin-like growth factor 1 (IGF-1). This is because IGF-1 is a hormone that is primarily produced in the liver in response to growth hormone (GH) secretion from the pituitary gland. It functions as a mediator of many of the growth-promoting effects of GH.

Measuring IGF-1 levels is particularly valuable because it remains elevated longer than growth hormone itself, which can fluctuate significantly throughout the day. Therefore, IGF-1 provides a more stable and reliable indication of chronic growth hormone activity and is considered a better parameter for diagnosing GH excess conditions, such as gigantism.

While growth hormone levels can also be assessed, they can be influenced by various factors, including the time of day, stress, and other physiological conditions, making initial assessment ambiguous. Prolactin and thyroid function tests, while they may be relevant in specific contexts, are less directly related to the growth mechanism in the case of gigantism. Thus, checking IGF-1 first provides a clearer picture of the child's hormonal status related to abnormal growth.