An client has pernicious anemia and has been receiving treatment for several years. what is the client lacking that results in pernicious anemia?

Pernicious anemia can be defined as a medical condition in which the body of the affected individual is unable to make enough of the healthy red blood cells. The lack of the vitamin B-12 in the body of the affected person results in this condition. It is treated by giving Vitamin B-12 pills to the patient.

Hence, the answer is 'Vitamin B-12'.