This case reports describes the presentation and management of a middle-aged patient with significant and chronic nutritional deficiencies (Vitamin B12) contributed to by a history of schizoaffective disorder. The patient presents acutely with altered mental state secondary to sepsis and severe anaemia. Upon acute stabilisation and completion of replacement therapy, subsequent laboratory monitoring demonstrated significant levels of thrombocytosis requiring an urgent transfer back to the acute hospital for further evaluation and management. This case demonstrates the phenomena of reactive thrombocytosis post- Vitamin B12 replacement in the context of severe malnutrition and B12 deficiency.