In most cases it is mandatory to have the rendering provider’s individual NPI in box 24J when submitting cms forms. However, there are a few cases when box 24J needs to be left blank.
Most Medicare carriers require that box 24J be left blank if the billing provider is an individual provider. In that case, the provider’s individual NPI, or type I NPI would be entered in both box 24J and in box 33a. If this NPI is the same, Medicare requires that the NPI is NOT entered in 24J but that 24J is left blank.
I truly do not know why they do this, but it is the rule. So if you are submitting paper claims to Medicare for an individual provider who bills under just an individual NPI, or type I NPI, and Medicare has been denying your claims, that may be why. If the provider gets paid under a group NPI then you would put the individual NPI of the rendering provider in box 24J.