Hello I hope someone could give enlightment as some people here are more expert. What would be the cause of low ion calcium but normal total and serum calcium? My doctor said my serum calcium would be normal and yes its always normal but ion is low because theres a problem. and its correlated to hyperexcitability. He didnt explain more and said Therefore i should supplement with extra calcium. Even though calcium in blood is normal but only little that can be taking up by cell/ready to use. What i know is the ion is the active form. Also on google i read it correlated with PTH. My thyroid blood test came up normal though. This is still a puzzle to me as why/what makes. Is it same as the vit d active form d25 and d 1,25. It cant be converted? My d 25 is low instead. Thank you in advance.