Ordering folate assays is no longer justified for investigation of anemias, in folic acid fortified countries

During the period of 1940-60, folate deficiency in a patient was not recognized until it had advanced enough to cause megaloblastic anemia. With the development of folate assays, folate deficiency could be identified much earlier. These assays provided data which showed the high prevalence of folate deficiency in: pregnancy, premature infants, hemolytic anemias, malabsorption syndrome and alcoholics. Furthermore, research showed a link between folate deficiency and pregnancy complications such as abruptio placenta, eclampsia, congenital malformations, especially neural tube defect (NTD), hyperhomocysteinemia, occlusive cardiovascular disorders and neuropsychiatric disorders. Serum folate (SF) and red cell folate (RF) became commonly ordered tests, for investigation of anemias and conditions cited above.

In 1996, in order to reduce the development of NTD, US Food and Drug Administration mandated that by January 1, 1998 all grain products must be fortified with 0.14 mg of folic acid per 100 g of grain [1]. Health Canada also mandated a similar folic acid fortification of grain products with the deadline of November 1, 1998 [2]. At that time, it was estimated that such fortification of grain products would add an average of 0.1 mg folic acid to the daily intake of folate by adults. This mandatory fortification of grain products markedly reduced the prevalence of folate deficiency and increased the mean SF and RF of the population [3–7].

In February, 2002, one of us (AMS), after noticing that in the year 2001, less than 1% of folate assays performed were low, notified the physicians and the wards at St. Boniface General Hospital (SBGH) that "Since mandatory fortification of grain products with folic acid, folate deficiency has become extremely rare. Consequently, the laboratory would no longer accept an order for folate assay, unless the physician could justify ordering these tests". Subsequently, Health Science Centre (HSC) and all other public laboratories (laboratories located in hospitals) in the province of Manitoba, discontinued providing folate assays and referred the tests to SBGH. SBGH remained the only public laboratory for performance of folate assays in the Province of Manitoba, Canada. This policy resulted in marked reduction of folate assays performed at SBGH for all public laboratories in Manitoba. Consequently, we decided to find out whether there was any need for folate assays for investigation of anemias.

This was a retrospective study of folate data and a review of all medical records of the patients with low SF or RF at HSC and SBGH, the two teaching hospitals in Manitoba. According to the policy at the time, the approval of the Medical Director and Director of Health Records of the two institutions was obtained prior to review of patient's records.

SBGH had been using the same L. Casei microbiological assay of serum folate and red cell folate since 1966. SF was determined using the method of Waters and Mollin [8]. RF was determined by measuring SF and whole blood folate and calculating the red cell folate [9]. SBGH data was used to determine the changes in SF and RF before and after folic acid fortification. During 2001, HSC was using a competitive binding assay of folate (IM_X system, Abbott Laboratories Diagnostic Division, Abbott Park, Il). Normal range for this assay was established in 1997. HSC data was used to demonstrate the prevalence of low SF and low RF post folic acid fortification era.

KvK reviewed all the folate assays performed at HSC in 2001 and reviewed the hospital records of those who had low SF or RF, to find out the cause of low folate and relation of the low folates to the patient's anemia. AMS, using the laboratory information system (LIS), reviewed all folate assays performed at SBGH for the periods 1996-2004 and reviewed the hospital records of only those who had low RF, to see if there was any explanation for low RF or any hematological abnormality to support the diagnosis of folate deficiency anemia (macrocytosis and/or increased number of hypersegmented polymorphs or megaloblastic changes in the bone marrow).

Fortification of grain products with folic acid was mandated in order to add about 0.1 mg folate to the daily intake of an adult. Some studies have shown that the resulting increase, in daily folate intake, is about 0.2 mg [10, 11]. Even if a patient has no other source of folate intake, a daily intake of 0.1 mg folic acid is more than enough to prevent folate deficiency anemia. In fact, patients with folate deficiency megaloblastic anemia can be treated with as little as 0.025 mg [12] or 0.050 mg [13] of folic acid daily.

Only 11 of 2154 (0.5%) SF assayed at HSC during 2001 were subnormal. In none of these patients, was the SF as low as is seen in patients with folate deficiency anemia. Similarly, in none of the patients seen at SBGH after 1998, could the anemia or macrocytosis be attributed to folate deficiency. In the National Health and Nutrition Examination Survey (NHANES) of 1999-2000 in USA [6, 7], the prevalence of low SF (<6.8 nmol/L) was 0.5% (compared to 16% in NHANES III for the period of 1988-1994) [6]. The prevalence of low SF and low RF reported by a large private Laboratory in Canada, during the period of February 1, 1999 to March 31, 2000 were 0.22% and 0.41% respectively [5]. Latif and colleagues [14] from Cleveland Clinic found 77 of 4985 (1.6%) SFs during 2001 were lower than normal. The MCV of these 77 patients was not different from those with normal SF. Only 39 of 74 patients with low SFs (0.9% of clinically suspected folate deficient patients) were actually prescribed folic acid. They commented that true folate deficiency is very rare; and questioned whether there is a role for folate determinations in clinical practice in the USA [14]. The prevalence of subnormal SF at HSC during 2001 (0.5%) was similar to prevalence of low SF in random population survey 1999-2000 of NHANES (0.5%) [6]. Joelson et al [15] reviewed the red cell folate data of 3 USA county hospitals with large cohort of indigent patients, during the years 1997, 2000 and 2004. Cutoffs for RF in these hospitals were 362 and 213 nmol/L. Using a RF cutoff 362 nmol/L, the combined incidence of folate deficiency decreased from 4.8% in 1997 to 0.6% in 2004. At a cutoff of 213 nmol/L, the incidence dropped from 0.98% to 0.09% [15]. They concluded that routine folate measurements for patients with anemia and/or macrocytosis is difficult to justify.

Our data show that, in the countries where grain products are fortified with folic acid, ordering serum or red cell folate for the investigation of anemia is a waste of time and resources. Low SF or RF are very rare and even in the few cases in which they are low, it is highly unlikely that they could be low enough to cause anemia. More importantly, the result of these tests is more likely to mislead the physicians than to provide any useful information.