Table 2.

An example of differing characteristics among E2 indirect and direct immunoassays

Assay methodE2 detection limit (pg/mL)Serum volume required (mL)Correlation coefficient (95% CI) with GC-MS/MS*Correlation coefficient (95% CI) with GC-MS/MS
GC-MS/MS0.61.0
Extraction/chromatographic2.01.00.88 (0.79-0.94)
RIA§
Extraction only0.80.50.94 (0.88-0.97)0.89 (0.81-0.93)
RIA
Extraction/chromatographic1.80.50.91 (0.82-0.95)
RIA
Direct RIA**1.40.20.83 (0.70-0.91)0.65†† (0.52-0.76)
Direct RIA‡‡2.20.20.70 (0.49-0.83)
Direct immunoassay§§5.00.30.57 (0.31-0.75)
Direct immunoassay∥∥2.70.070.71 (0.50-0.84)
  • * Reference 18 is a pilot study in 40 postmenopausal women.

  • Reference 18 is a confirmatory study in 374 postmenopausal women.

  • SFBC Taylor Technologies, Inc.

  • § Esoterix Endocrinology, Inc.

  • Royal Marsden Hospital Research Laboratory (M. Dowsett).

  • University of Southern California research laboratory (F.Z. Stanczyk); 0.8 mL serum used in ref. 19.

  • ** Diagnostic Products Corporation.

  • †† Correlation significantly different from that between RIA and GC-MS/MS (P < 0.01).

  • ‡‡ Diagnostic Systems Laboratories.

  • §§ Roche Diagnostics, Inc.

  • ∥∥ Ortho-Clinical Diagnostics.