Clinical and Interpretive

This assay is useful for ascertaining whether ovulation occurred in a menstrual cycle, the evaluation of placental function in pregnancy, and in workup of some patients with adrenal or testicular tumors.

Sources of progesterone are the adrenal glands, corpus luteum, and placenta.

Adrenal Glands:
Progesterone synthesized in the adrenal glands is converted to other corticosteroids and androgens and, thus, is not a major contributor to circulating serum levels unless there is a progesterone-producing tumor present.

Corpus Luteum:
After ovulation, there is a significant rise in serum levels as the corpus luteum begins to produce progesterone in increasing amounts. This causes changes in the uterus, preparing it for implantation of a fertilized egg. If implantation occurs, the trophoblast begins to secrete human chorionic gonadotropin, which maintains the corpus luteum and its secretion of progesterone. If there is no implantation, the corpus luteum degenerates and circulating progesterone levels decrease rapidly, reaching follicular phase levels about 4 days before the next menstrual period.

Placenta:
By the end of the first trimester, the placenta becomes the primary secretor of progesterone.

Ovulation results in a mid-cycle surge of luteinizing hormone (LH) followed by an increase in progesterone secretion, peaking between day 21 and 23. If no fertilization and implantation has occurred by then, supplying the corpus luteum with human chorionic gonadotropin-driven growth stimulus, progesterone secretion falls, ultimately triggering menstruation. A day 21 to 23 serum progesterone peak of 6.5 to 7 ng/mL is the minimal level considered consistent with ovulation. A level in excess of 18 ng/mL is considered conclusive proof of ovulation.

Placental insufficiency has been associated with low levels of LH and progesterone.

Levels of LH and progesterone may be increased in some adrenal or testicular tumors.

Assessment of the function of the corpus luteum requires correlation with the phase of the menstrual cycle.

In patients receiving therapy with high biotin doses (ie, >5 mg/day), no specimen should be drawn until at least 8 hours after the last biotin administration.

As with all tests containing monoclonal mouse antibodies, erroneous findings may be obtained from specimens drawn from patients who have been treated with monoclonal mouse antibodies or have received them for diagnostic purposesIn rare cases interference due to extremely high titers of antibodies to ruthenium and streptavidin can occur.