See the troubleshooting guide for managing reactions
The benefits of B12 shots are most pronounced in those with a B12 deficiency
Severe reactions are rare but can occur
As is true of the proprietary mixes discussed earlier, every clinic uses a different cocktail
And conditions that lead to low stomach acid also lead to a myriad of nutrient deficiencies, including B12 deficiency
The GP will take a detailed history including: Current medications and supplements (particularly B12 injections or high-dose oral preparations) Alcohol consumption and risk factors for liver disease Personal or family history of haematological disorders or cancer Symptoms suggesting underlying pathology Recommended investigations: Patients with unexplained elevated B12 should undergo: Repeat B12 measurement to confirm persistence, ideally timed away from recent injections or high-dose supplements Full blood count (FBC): To identify polycythaemia, leucocytosis, or other haematological abnormalities Liver function tests (LFTs): Including ALT, AST, ALP, bilirubin, and albumin to assess hepatic function Renal function tests: Urea, creatinine, and estimated glomerular filtration rate (eGFR) Lactate dehydrogenase (LDH): Elevated in haemolysis, liver disease, and some malignancies Further investigations may include: Abdominal ultrasound or CT scanning if liver disease or malignancy suspected Haematology referral for bone marrow examination if myeloproliferative disorder considered Liaison with the laboratory if results conflict with the clinical picture, as immunoassay interference (e.g., macro-B12) may occur In specialist settings, measurement of holo-transcobalamin or B12-binding proteins may be considered The urgency of investigation depends on clinical features and suspected underlying conditions
