Evaluation of a dried blood spot assay to measure prenatal screening markers pregnancy-associated plasma protein a and free β-subunit of human chorionic gonadotropin.

BACKGROUND First-trimester prenatal screening for aneuploidy by use of dried blood spots (DBSs) may offer practical benefits in settings where the instability of intact human chorionic gonadotropin (hCG) is problematic. We evaluated a DBS pregnancy-associated plasma protein A (PAPP-A) and free β-subunit of hCG (free hCGβ) dual assay and compared it to serum screening. METHODS Hematocrit-corrected DBS PAPP-A and free-hCGβ concentrations were measured and compared with serum concentrations in 252 first-trimester samples. Serum intact hCG was also measured and, with serum free hCGβ, was used to fit a model to predict serum-equivalent DBS free-hCGβ concentrations. In a separate experiment, we investigated the effects of temperature and relative humidity during the blood spot drying process. RESULTS The DBS assay for PAPP-A performed similarly to the serum assay, whereas free-hCGβ DBS measurements were consistently higher than in serum. Purifying blood spots of intact hCG suggested that the free-hCGβ DBS assay is measuring a composite of free hCGβ and additional β-subunits from intact hCG. The drying experiment showed that increased temperature and relative humidity during the drying process resulted in increased free hCGβ and reduced PAPP-A. CONCLUSIONS Despite measuring additional free hCGβ compared to the serum assay, DBS analysis has a role in first-trimester combined screening for trisomy 21.