How do I test my progesterone levels?

Methods for Testing Progesterone Levels

Blood testing is the primary and most reliable method for measuring progesterone levels, with samples ideally collected during days 21-26 of the menstrual cycle for optimal diagnostic accuracy.

Blood Testing: The Gold Standard

Blood testing is the most commonly used and validated method for measuring progesterone levels. This approach offers several advantages:

• Timing is critical: For accurate assessment, blood samples should be collected during days 21-26 of the menstrual cycle, not during the midluteal phase as previously thought 1
• Discriminatory level: A serum progesterone level of 21 nmol/L during days 25-26 provides a test with 81% sensitivity and 73% specificity for diagnosing luteal phase defects 1
• Clinical interpretation:
  • Luteal phase serum progesterone levels between 2-10 ng/ml indicate corpus luteum dysfunction
  • During early pregnancy (first 10 weeks), levels below 15 ng/ml suggest corpus luteum dysfunction 2

Laboratory Testing Requirements

The American Society of Clinical Oncology (ASCO) and College of American Pathologists (CAP) have established guidelines for progesterone receptor testing that highlight important considerations for laboratory handling of samples:

• Sample handling: Time from tissue acquisition to fixation should be as short as possible 3
• Fixation process: Samples should be fixed in 10% neutral buffered formalin (NBF) for 6 to 72 hours 3
• Sample preparation: Tissues should be sliced at 5-mm intervals and placed in sufficient volume of fixative 3
• Documentation: Cold ischemia time, fixative type, and time placed in fixative must be recorded 3

Quality Control Measures

To ensure accurate results, laboratories must implement:

• Internal controls: Normal tissue elements should show appropriate staining patterns 3
• External controls: Multiple tissues with expected strong staining, lower limit of detection levels, and negative controls should be included 3
• Validation procedures: Initial test validation/verification prior to reporting any clinical samples 3
• Proficiency testing: Mandatory participation in external proficiency testing programs 3

Common Pitfalls and Considerations

• Timing affects accuracy: Progesterone levels fluctuate throughout the menstrual cycle, making timing of the test critical for proper interpretation 1
• Route of administration affects levels: When monitoring therapeutic progesterone, be aware that oral, vaginal, and intramuscular administration result in different serum levels 4, 5, 6
• Declining response to vaginal administration: With vaginal progesterone suppositories, there is a smaller rise in serum progesterone with continued use over time 6
• Storage limitations: Storage of slides for more than 6 weeks before analysis is not recommended for immunohistochemical testing 3

Clinical Applications

• Luteal phase defects: Serum progesterone measurement is useful for diagnosing luteal phase deficiency, a frequent cause of recurrent spontaneous abortion 1
• Monitoring therapy: Serial measurements can be used to monitor response to progesterone therapy in patients with corpus luteum dysfunction 2
• Pregnancy support: In threatened abortion, progesterone levels can help identify patients who might benefit from supplementation 2

Blood testing remains the most reliable and clinically validated method for assessing progesterone levels, with careful attention to proper timing and laboratory handling being essential for accurate results.