What is luteinizing hormone (LH)?
Luteinizing hormone (LH) is a pituitary gland hormone that signals the testes to produce testosterone; abnormal LH levels help clinicians differentiate primary hypogonadism (testicular failure) from secondary hypogonadism (pituitary or hypothalamic dysfunction).
The pituitary gland releases luteinizing hormone to direct the testes to synthesize and release testosterone. This hormone-signaling chain, called the hypothalamic-pituitary-gonadal (HPG) axis, is essential for maintaining male sexual function and secondary sex characteristics. In the context of testosterone replacement therapy evaluation, LH measurement serves as a critical diagnostic tool.
When a patient presents with low testosterone, LH levels reveal whether the problem originates in the testes themselves (primary hypogonadism) or in the pituitary or hypothalamus (secondary hypogonadism). In primary cases, the testes fail to respond adequately, so LH rises as the pituitary attempts to compensate. In secondary cases, the pituitary fails to produce enough LH, leaving testosterone production deficient. This distinction guides treatment decisions and helps clinicians understand whether replacement therapy addresses the root cause or compensates for impaired signaling.
Most TRT clinics in Florida order LH as part of baseline bloodwork alongside total and free testosterone, prolactin, and other hormones. The test is straightforward and inexpensive, making it a standard component of any hypogonadism workup. Providers use LH results alongside clinical history and other labs to confirm diagnosis and monitor response to therapy over time.