Low or Low-Normal Insulin-Like Growth Factor 1 After Traumatic Brain Injury: Interpretation and Implications

Growth hormone deficiency (GHD) is a prevalent consequence of traumatic brain injury (TBI) that can contribute to prolonged adverse symptoms and impaired quality of life. The overlap between symptoms of GHD and chronic TBI complicates the clinical picture, highlighting the need for precise diagnostic tools. Insulin-like growth factor 1 (IGF-1), a key mediator of growth hormone (GH) activity, is frequently utilized as a surrogate marker of GH status. However, IGF-1 levels may be normal in patients with confirmed GHD. Furthermore, low or low-normal IGF-1 is not specific to GHD, and provocative testing is required to confirm GHD in most patients with suspected deficiency. To provide a pragmatic clinical framework for interpreting IGF-1 z -score