Getting a high MCV level (above 100 fl) in your blood test typically suggests macrocytic anemia. Macrocytic anemia is a blood disorder characterized by abnormally large RBCs and can be linked to several health conditions, including intake of specific drugs. That said, having high MCV levels can be due to the following reasons:

Vitamin B12 or B9 Deficiency

Lack of vitamin B12 (cobalamin) and vitamin B9 (folate) causes deformities and size disparity in the RBCs. After all, both vitamins are involved in producing red blood cells in the bone marrow. 

If you have high MCV levels, it may be time to increase your uptake of foods rich in vitamins B12 and B9 or include supplementation as advised by your healthcare provider.

Autoimmune Gastritis

Elevated MCV is also observed in patients with autoimmune gastritis. It is a chronic disease characterized by the inflammation of the stomach’s upper section containing the body and fundus. 

The immune system mistakenly attacks the cells in the stomach lining. Autoimmune gastritis leads to folate deficiency, causing macrocytic anemia or macrocytosis–which translates to high MCV levels in the blood test. 

Since it’s an autoimmune form of gastritis, the true cause of the condition remains undetermined. You’ll likely develop autoimmune gastritis if someone in your family already has the disorder.