We ran a specificity/selectivity qPCR for plasma DNA samples. For specificity we added mastermix only into the plasma and had all samples come back with 0 signal (expected). For selectivity, we spiked in 100 copies/reaction into each plasma sample, and all 3 plasma samples came back with a concentration of ~300 copies/rxn. A spike check was also performed in which we spiked in 100 copies/reaction into water, not plasma, and the spike-check came back at 100 copies/reaction. Why would I see an over-recovery of 300% in the plasma?