Hi,
Your father must be suffering severe anemia associated with 
diabetic nephropathy due to 
chronic diabetes. 
Diabetes mellitus is the condition in which the individual will not produce enough insulin in the blood to clear the high blood glucose. In chronic condition, high blood glucose progressively damage all organs in the body. Diabetic nephropathy is the condition in which the normal filtration function of the 
glomerulus in the kidney is damaged because of high blood glucose level. When there is sufficient amount of glomeruli get damaged, the kidney failure may occur.
Kidney failure results in increased blood pressure. It also affects the cardiovascular system. Regular dialysis is needed to clear the blood of toxic metabolites which are normally excreted by the kidney. Kidney failure also causes decreased 
erythropoietin response to anemia. Erythropoietin is an hormone helps in the synthesis of RBCs. Prolonged renal compensation results in severe anemia and immunocompromise.  I suggest 
complete blood count, renal function test to identify the possible etiology for severe anemia. Anemia in 
renal failure often associated with low iron content in the body. Functional renal assessment to be done by renal function test.
Take care. Hope I have answered your question. Let me know if I can assist you further.
Regards,
Dr. Pradeepraj, General & Family Physician