Free Progesterone

Clinical Significance:
Progesterone is a Progestin produced primarily from enzymatic metabolism of Pregnenolone.  It is enzymatically converted to 17-Hydroxy Progestrone and 11-Deoxycorticosterone.  It is secreted by both the gonads and the adrenal glands.  It is mostly bound to Cortisol Binding Globulin and Albumin, but a small percentage is present in the “Free” form.  This “Free” Progesterone is the bioactive moiety.  It is excreted into the urine primarily as “Free” unconjugated Progesterone and as Pregnanediol. Progesterone is responsible for cellular changes in the cervix, vagina, and uterus.  Levels are lowest in the follicular phase and increase rapidly following the luteal surge.  Increased Progesterone inhibits ovulation.  “Free” Progesterone increases greatly during pregnancy reaching about 20% of the total Progesterone concentration at delivery.  Measurement of Progesterone can be useful to monitor fertility, corpus luteum function, endometrial development, and be helpful in in-vitro fertilization patients.

Reference Ranges:
Male:                              5 – 20 ng/dl
Female:                          up to 50 ng/dl
Luteal:                           Up to 900 ng/dl
Pregnancy:                     50 – 2000 ng/dl

“Free” Progesterone is measured by radioimmunoassay.

Patient Preparation:
Patient should not be on any Corticosteroid, ACTH, Estrogen, or Gonadotropin medication, if possible, for at least 48 hours prior to collection of specimen.

Specimen Collection:
3 ml serum or EDTA plasma should be collected and separated and frozen as soon as possible. Minimum specimen size is 2 ml.

Shipping Instructions:
Ship specimens frozen in dry ice.

1. S Batra, LP Bengtsson, H Grundsell, and N-O Sjoberg.  Levels of Free and Protein-Bound Progesterone in Plasma during Late Pregnancy.  Journal of Clinical Endocrinology and Metabolism 42:  1041, 1976.

2. CJ Munro, GH Stabenfeldt, JR Cragun, LA Addiego, JW Overstreet, and BL Lasley.  Relationship of Serum Estradiol and Progesterone Concentrations to the Excretion Profiles of Their Major Urinary Metabolites as Measured by Enzyme Immunoassay and Radioimmunoassay.  Clinical Chemistry 37: 38-44, 1991.