We have an in-house CRP ELISA assay that takes approximately 6 hours to run from addition of sample to wells to reading the absorbance on a microplate reader. I simultaneously ran both our in-house ELISA CRP assay and the CRP Human SimpleStep ELISA on the same set of 30 DBS samples, nine DBS standards, and serum standards provided with the SimpleStep kit. For our regular CRP assay, we elute one 1/8" round punch from a larger dried blood spot on filter paper in 250 ul of phospate buffer with 0.1% TWEEN and load 100 ul per well, which corresponds to a dilution factor of approximately 167-fold. Because of the incredible sensitivity of the SimpleStep kit, I made an additional 1:100 dilution for all DBS samples for a final dilution of around 16 700. From start to finish, the Simple Step assay took about 90 minutes - the time that it took to finish the first incubation step of our inhouse assay. The instructions were extremely easy to follow, both the serum standard curve and dried blood spot standard curves had a R2 value of 1, and the sample values showed excellent correspondence with those obtained using our in-house assay (R2 = 0.95). The intra-assay CV for replicate wells was an impressive 3.21% versus the 7.9% for our in-house assay.
The only drawback of this kit is the extra time required to dilute samples down to pg/mL levels, as serial dilutions are required however, the ease of use and substantial overall time savings more than compensate for this drawback.