Which laboratory is recommended for testing progesterone levels?

Laboratory Testing for Progesterone Levels

Progesterone levels should be measured in a CAP-accredited laboratory or one meeting equivalent accreditation standards, using validated immunoassay methods or liquid chromatography-tandem mass spectrometry (LC-MS/MS), with the laboratory demonstrating proficiency through external quality assurance programs.

Laboratory Accreditation Requirements

The laboratory performing progesterone testing must be CAP-accredited or meet equivalent accreditation requirements to ensure accuracy and reliability of results 1. Key requirements include:

• Participation in mandatory proficiency testing programs with at least two testing events per year, achieving ≥90% correct responses on graded challenges 1
• On-site inspection every other year with annual self-inspection requirements 1
• Documented competency assessment of all testing personnel and pathologists performing the assays 1
• CLIA compliance with enhanced scrutiny beyond standard regulatory requirements 1

Recommended Testing Methods

Primary Methodologies

Immunoassay platforms are the most commonly used methods in clinical laboratories:

• Chemiluminescence immunoassay (CLIA) is the most sensitive immunoassay method currently available 2
• Enzyme-linked immunosorbent assay (ELISA) using microplate format provides reliable results when properly validated 3, 4
• Automated immunoassay analyzers from different manufacturers can be used, though precision varies significantly between platforms 3

Gold Standard Method

Isotope dilution liquid chromatography-tandem mass spectrometry (ID LC-MS/MS) serves as the primary reference method:

• Provides superior precision with repeatability of 1.1% and reproducibility of 0.14% 2
• Detection limit approximately 0.6 μg/kg 2
• Expanded uncertainty approximately 2.6% within 95% confidence limits 2
• Should be used to validate immunoassay methods 2

Critical Quality Considerations

Method-Specific Interpretation

Progesterone threshold values must be interpreted based on laboratory- and method-specific data, as significant variability exists between platforms 3:

• Mean progesterone levels differ across multiple analyzers even when measuring identical samples 3
• Only 50% of automated immunoassay analyzers achieve intraassay coefficients of variation <10% at all time points 3
• Only 50% achieve interassay coefficients of variation <10% 3
• Agreement between immunoassay and LC-MS/MS is generally high (correlation >0.90), but absolute values may differ 2, 3

Validation Requirements

Laboratories must validate their progesterone assay against clinically validated reference methods 1:

• Initial concordance must be ≥90% for positive results and ≥95% for negative results when compared to validated assays 1
• Revalidation required whenever significant changes occur to the test system (antibody clone, antigen retrieval, detection systems) 1
• Regular ongoing reassessment should occur at least semiannually 1

Quality Assurance Measures

Optimal internal quality control procedures must include 1:

• Routine use of external control materials with each batch of testing
• Standardized operating procedures documented and followed consistently
• Initial and ongoing personnel training with competency assessment
• Regular equipment maintenance protocols

Clinical Context for Serum Progesterone Testing

When ordering progesterone testing, consider the following clinical applications 5:

• Serum estradiol and progesterone levels should be measured to quantify hormonal status, though normal ranges vary significantly by age, gender, and menstrual cycle phase 5
• Additional hormonal measurements (LH, prolactin, FSH) may be needed to establish etiology of hormonal abnormalities 5
• Liver and renal function tests should be obtained as the liver metabolizes progesterone and estrogen 5

Common Pitfalls to Avoid

• Do not assume all laboratories provide equivalent results - significant inter-laboratory variation exists even with the same methodology 2, 3
• Do not apply universal threshold values across different laboratory platforms without validation 3
• Ensure the laboratory participates in external proficiency testing - laboratories without this oversight have higher error rates 1
• Verify the laboratory uses validated progesterone standards incorporated into daily immunoassays to improve accuracy 3