Systematic Reduction in Estradiol and Testosterone Measurements due to Serum Separator Gel in Blood Collection Tubes: Implications for At-Home Fertility Testing.

Background: Data on the efficacy of at-home capillary testing is limited. We compared 9 fertility-associated analytes [anti-Müllerian hormone, follicle-stimulating hormone, free thyroxine, luteinizing hormone, estradiol (E2), prolactin, sex hormone-binding globulin, thyroid-stimulating hormone, and total testosterone (T)] to assess concordance between venous and capillary tubes and the impact of serum separator gel.

Methods: Two trials were conducted. The first (trial 1) used 34 paired blood samples taken from 13 participants collected into 2 capillary storage tubes: serum clot activator tubes (cS-CAT) without serum separator gel and serum separator clot activator tubes (cSS-CAT) with serum separator gel. Trial 2 collected 27 sets of 4 blood samples from 26 participants into cS-CAT, cSS-CAT, venipuncture serum clot activator tubes (vS-CAT) without serum separator gel, and venipuncture serum separator clot activator tubes (vSS-CAT) with serum separator gel. Measurements of the analytes were log-transformed, and each tube type was compared via paired t-tests.

Results: Significantly lower measurements for both E2 and T (13% and 8%, respectively) were observed for cSS-CAT compared to cS-CAT. Differences were greater between cSS-CAT and vSS-CAT (17% and 11%) and greatest between cSS-CAT and vS-CAT (19% and 14%). No significant differences were observed for the other 7 analytes nor when comparing cS-CAT to vSS-CAT. Additionally, conversion formulas were developed to adjust E2 and T measurements between the most divergent tube types.

Conclusions: Capillary blood collection tubes with gel systematically lower E2 and T measurements, showing discrepancies with venous blood collection tubes. These effects did not impact other analytes.