Diagnostic value of the serum folate assay

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Abstract
The diagnostic value of the serum folate assay has been assessed in 90 patients, each of whom had a macrocytic anaemia and a low serum vitamin B12level. Twenty-nine (32%) patients were found to have anaemia due primarily to folate deficiency. The cause of the low serum vitamin B12levels is uncertain in the 22 (25%) patients with normal or borderline vitamin B12absorption. The effect of folic acid therapy was studied in four of these patients, and in each case the serum vitamin B12rose slowly to a normal level.The serum folate was low in only four (7·5%) of the 54 patients with pernicious anaemia, and the levels rose to normal on treatment with vitamin B12alone. A high serum folate occurred in eight (15%) pernicious anaemia patients. A normal serum folate indicated the diagnosis of pernicious anaemia or megaloblastic anaemia following partial gastrectomy. However, a normal serum folate and a very low vitamin B12level was found in two patients with idiopathic steatorrhoea.It is concluded that the serum folate assay is a valuable routine test in patients who have a macrocytic anaemia and low serum vitamin B12. A low folate level makes the diagnosis of pernicious anaemia unlikely and is a strong indication for full investigation of small intestinal function.