Can a cbc detect vitamin deficiency like b12? or do you need a specific blood test ?

Can raise suspicions: Large red blood cells on a CBC, even if you aren't anemic can raise suspicions of B12 or Folate (folic acid) deficiency. Then your doctor can perform B12 or Folate (folic acid) assays. If RBC are normal size, deficiency is unlikely. Thanks for trusting HealthTap!

Red blood cell size: A CBC includes a test called the MCV (mean corpuscular volume). If the MCV is too high, that can indicate a Vit. B-12 and / or Vit B-6 deficiency. If the MCV is too low, then it can indicate an iron deficiency.