Background: Analysis of dried blood specimens has been an integral part of laboratory medicine dating back to the early 1960s when they were introduced as part of neonatal screening programs. More recently, they have been used in Down syndrome screening programmes. Dried blood spot specimens can be collected either by finger-stick or by traditional venipuncture and spotted onto filter paper. We sought to evaluate whether first-trimester free Beta hCG and PAPP-A multiples of the median (MoMs) were different in dried blood specimens collected via finger-stick compared to specimens collected via venipuncture.
Methods: A total of 2786 consecutive dried blood specimens were evaluated including 2144 collected using finger-stick and 644 specimens collected using venipuncture and spotted onto filter paper. Linear regression was used to assess the overall impact of collection method on dried blood free Beta hCG and PAPP-A and the impact of collection method on the trend of dried blood free Beta hCG and PAPP-A with transport time.
Results: For finger-stick and venipuncture, the median for free Beta hCG MoM was 0.99 and 1.04, respectively while the median PAPP-A MoM was 1.00 and 1.01, respectively. The regression formula for free Beta hCG was ln(MoM) = -0.00918 + 0.05112×Venipuncture + 0.00299×Days -0.00983×Days×Venipuncture and for PAPP-A the formula was ln(MoM) = -0.01000 + 0.04779×Venipuncture -0.00051×Days -0.02117×Days×Venipuncture. None of the coefficients were significant.
Conclusions: Collection method does not impact MoM values. Thus, centres have flexibility in the collection method utilized while being able to use a single reference database for all dried blood specimens.
Keywords: Pregnancy; immunoassay; quality assurance and control.