qPCR primer correlation coefficient

[Caterina Iofrida]

Hello,
I have a problem with the set-up of some real-time PCR primers. I usually test
primer efficiency by performing PCR reaction on five cDNA dilution points (1:5
dilutions: from not diluted to 1:625). The correlation coefficient (R) should be
at least 0,989 or higher, as reviewed by literature. But my primers, even if the
efficiency is good (comprised between 90% and 110%), have a correlation
coefficient lower than 0,989, more specifically the lower value is 0,982 for a
primer pair and the others have higher but near values. Since now, I have never
had this kind of problem with primer set-up. I have tried also testing primers
on five 1:3 dilutions, from 1:3 to 1:243 but it didn't help. I perform qRT-PCR
with iQ™ SYBR® Green Supermix - (Bio-Rad) using iCycler iQ real-time detection
system. Has anyone had similar results?
Thank you very much

Caterina Iofrida