RRBC folate, like haemoglobin A1C in blood glucose monitoring, provides information about folate status over the lifetime of RBCs. If RBC folate testing is used, approximately 5% of people with normal serum folate levels may have evidence of folate deficiency. This test is almost always a part of a complete blood count (CBC) test. A red blood cell count is a blood test to find out how many red blood cells (RBCs) you have. It’s also known as an erythrocyte count.