LH is a glycoprotein hormone produced by the anterior pituitary gland and is part of the same biochemical family as FSH, TSH, and hCG. It is composed of alpha and beta subunits; the beta subunit gives LH its receptor specificity. Clinical assays for LH were developed in the mid-1900s and later refined to provide reliable measures across the menstrual cycle and in different life stages. Biologically, LH acts on specific receptors in the gonads. In people assigned female at birth, LH contributes to the final maturation of ovarian follicles and triggers the ovulatory surge; in people assigned male at birth, LH stimulates Leydig cells to support testosterone synthesis. LH levels reflect the balance of pituitary signaling and gonadal feedback and operate within the larger hypothalamic–pituitary–gonadal axis.

Elevated LH levels may reflect increased pituitary signaling relative to gonadal feedback or normal cyclic peaks such as the midcycle surge; they can also appear when the gonads respond less to stimulation. Low LH levels may reflect suppressed pituitary output, strong feedback from sex hormones, certain medications or hormone therapies, or specific cycle phases. Interpreting high or low LH is most informative when reviewed with related markers (FSH, estradiol, testosterone, prolactin) and clinical context such as cycle phase, age, and medication use.

LH is included in the Foundation Zoomer to assess reproductive endocrine signaling and how the pituitary and gonads interact. As part of the Hormone Endocrine domain, LH helps clarify cycle timing, sexual hormone balance, and patterns that may underlie symptoms like changes in energy, mood, libido, or menstrual irregularity. Combined with other markers, LH supports a systems-based, personalized baseline for care.