Both I and another investigator have performed this assay and our experimental values are about 5 fold lower than expected.  I also get a 5 fold lower result when glycerol is used instead of serum.  I perform a 5-point standard curve with each assay and it is very similar each time.  I have searched Wako's website and e-mailed tech support (with no response) trying to find typical values for the standard curve but could not find anything.