I measure plasma osmolarity (mice) using freezing point method and I get values around 350mosm/kg while in literature it's normally around 300mosm/kg. Everyone in my lab gets results that are similar to my values. Our osmometer was recently checked by a company, we calibrate it with fresh solutions before each experiment, plasma is fresh.
Do you think the fact that I measure slightly higher values on regular basis is a problem for an experiment that is focused on rather relative change of osmolarity under different conditions?
I think the fact that you measure slightly higher values on a regular basis means you have big time problems, and not problems that are solvable by any conventional means. You're gonna have to take action on this -- and fast.