Nilsson-Ehle H. Sacred cows slaughtered – functional vitamin B₁₂ deficiency. Rondel 2001; 9:Evaluation (www.rondellen.net)

"Functional vitamin B₁₂ deficiency"?

Anne-Mette Hvas, MD at Aarhus University, Denmark, defended the PhD thesis "Diagnosis of vitamin B12 deficiency" on the 27^th of September this year. The introduction of Methylmalonic acid (P-MMA) for the diagnosis of vitamin B₁₂ deficiency in a couple of Danish counties was evaluated in terms of diagnostic performance, clinical effects of vitamin B₁₂ therapy, actual and recommended usage of P-MMA and economic consequences. The well-known background is that some 15-20 % elderly subjects have been reported to have "subclinical" deficiency defined by the new plasma markers of "intracellular" cobalamin deficiency, P-MMA and homocysteine (P-tHcy). Non-hematological signs of deficiency are often diffuse and unspecific but may become irreversible if not treated. Published intervention studies in e.g. dementia are small, open, non-randomised and show contradictory results. Standard vitamin B₁₂ therapy lowers P-MMA also in subjects without clinical signs of deficiency, but the significance of this is incompletely understood. There is to date no single "gold standard" for the diagnosis of cobalamin deficiency.

There has been a tremendous increase in the number of P-MMA analyses and patients put on vitamin B₁₂ therapy in Denmark during the last decade; more so in the region of Aarhus University where most of the MMA research is performed. The question was raised whether these increases are clinically beneficial on a population basis. In other words, the specificity of a "high" P-MMA for the diagnosis of cobalamin deficiency was questioned. "High" P-MMA is seen in cobalamin deficiency, reduced renal function, thyroid disorders, abnormal gut flora and in pregnancy. The aims of the thesis could be summarized into five main topics:

1. What were the motives and reactions when performing a P-MMA analysis?
A survey of the records of patients with "high" P-MMA (198 hospital patients, 318 from primary health care) showed that a stated reason was lacking in 30-40 %, a reaction to the answer was missing in over 60 % of the hospital patients [1, 2]. "Screening", defined as test performed without clinical signs of deficiency, was common in primary health care, where P-B₁₂ often was substituted by P-MMA. Cobalamin therapy was often initiated only because of a "high" P-MMA. These results indicate an over-confidence in P-MMA as a "Gold standard" for B₁₂ deficiency.

2. Does a moderately increased P-MMA change over time in patients not treated with vitamin B₁₂?
In 432 pts with a moderately increased P-MMA (median 0.33 m mol/l, range 0.29-3.60 m mol/l), retesting was performed after 1-3.9 years. P-MMA decreased in 44 %, increased > 20% from baseline in 16 % of the patients, but only 3 % had P-MMA > 1.00 m mol/l at follow-up. There was a weak but statistically significant correlation between P-MMA, P- B₁₂ and P-tHcy [3]. A subgroup of patients (n=118) reported an extra daily vitamin supplementation corresponding to the daily need of vitamin B₁₂ and 200 m g of folic acid. In this group, there was an inverse relationship between vitamin intake and P-tHcy, but no correlations to P-MMA and P-B₁₂. The changes in P-MMA did not correspond to changes in serum creatinine (S-Crea). Thus, the hypothesis that a moderate increase in P-MMA indicates a condition that aggravates without B₁₂ therapy during a couple of years was rejected.

3. Does P-MMA correlate to clinical B₁₂ deficiency?
At follow-up, a thorough medical history, clinical and neurological investigation was performed in 403 patients [3]. Symptoms compatible with B₁₂ deficiency were common, but after adjustment for age and sex, such symptoms did not correlate to P-MMA, not even in subjects with "high" P-tHcy or "low" P-B₁₂. Similarly, there were no correlations between P-MMA and clinical findings (Neurological Disability Score). The lack of correlation between P-MMA and clinical findings indicates that such symptoms are usual in elderly patients with or without "high" metabolite concentrations. The need for randomised studies with clinical endpoints became obvious.

4. Does P-MMA correlate to renal function?
Renal insufficiency is a well-known cause for increased P-MMA, and now it was shown that S-Crea also within the reference interval correlated to P-MMA [4]. The observed inverse relationship between P-B₁₂ and P-MMA remained and was shifted due to S-Crea in e.g. 70-year-old women. According to a predictive model, a 70-year-old woman with an S-Crea of 50 m mol/l would have a P-MMA at the upper reference limit at a P-B₁₂ of approximately 90 pmol/l, the corresponding P-B₁₂ for an S-Crea of 100 m mol/l would be 250 pmol/l. Thus, S-Crea also within the reference interval must be taken into account when evaluating a single P-MMA value.

5. Does B₁₂ therapy have a positive clinical effect in patients with moderately elevated P-MMA?
In an intervention study, 140 patients with moderately elevated P-MMA (0.40 – 2.00 m mol/l) were randomised to four weekly intramuscular injections of 1 mg slow-release cyanocobalamin or placebo [5]. There was a significant decline in both P-MMA (63%) and P-tHcy (23%). However, there were no significant effects on symptoms, Hb, MCV, or neurological function in the whole group. In a subgroup with P-MMA >0.60 m mol/l or P-tHcy >15 m mol/l neurological symptoms (but not signs) were improved in the B₁₂ – treated group. The study patients reported significantly worse quality of life (QOL) than the Danish background population. QOL was, with one exception not improved by B₁₂ therapy [6]. The clinical benefit of B₁₂ therapy, at least in the short term, was thus questioned. Needless to say, longer intervention studies are required for a reliable answer to this important question.

Conclusion and unanswered questions

The probability that a moderately increased P-MMA per se means clinically significant B₁₂ deficiency showed to be much lower than expected, i.e. the specificity turned out to be disappointingly low. There was no consistent increase of P-MMA in patients with moderately elevated P-MMA left untreated for several years, there were no consistent correlations between P-MMA and symptoms/signs of B₁₂ deficiency, a randomised study failed to show any clinical benefit of B₁₂ therapy. Importantly, P-MMA must be correlated to S-Crea also within the reference range. In summary, the value of P-MMA as the only indicator of B₁₂ deficiency was questioned. P-MMA was judged unsuitable for screening purposes, and the results did not support initiation of (lifelong) B₁₂ therapy based an "increased" P-MMA only. Presumably, the low specificity is due to the fact that P-MMA was analysed also in patients lacking distinct signs and symptoms of deficiency. Previous studies of subjects with e.g. objective neurological signs of deficiency have shown a higher specificity.

The present results indicate that new diagnostic methods should be implemented systematically and in close collaboration between laboratories and physicians. The clinical decision limit for a "high" P-MMA should, based on these data, not be the same as the upper reference limit, perhaps not even the median + 3 SD for "healthy" subjects, which is commonly used.

The conclusion that B₁₂ therapy as such is ineffective requires, however, that the given therapy is adequately intense and long lasting. In the present study, one month of treatment was performed according to Danish recommendations (parenteral cyanocobalamin in a slow-release preparation), but there is a current debate regarding administration (parenteral, oral), cobalamin preparation (cyano-, hydroxo-, methylcobalamin) and dose intensity.

There was no diagnosis of any underlying gastrointestinal disorder for suspected B₁₂ deficiency, which not least earlier Swedish studies have shown to be important. To date, analysis of S-gastrin and S-pepsinogen are unavailable in Denmark.

Where do we go from here? In clinical practice, there is to date no evidence to support vitamin therapy of biochemical abnormalities in the absence of a clinical correlate. There is definitely a need for long-term randomised studies to determine the clinical benefit of B₁₂ therapy in subjects with "mild", "sub clinical" and suspected B₁₂ deficiency. Important risk groups for such studies, not least in elderly populations, are subjects/patients with clinically suspect B₁₂ deficiency. Subjects at risk for vitamin B₁₂ malabsorption, e.g. those with gastrointestinal disorder and surgical resections, ongoing medication (e.g. gastric acid inhibitors, biguanides), as well as those with malnutrition, should also be entered into such studies. Clinical endpoints in studies as well as in clinical practice should relate to the same organ systems (haematopoiesis, mucosae, nervous system) that are affected by the previously lethal (pernicious) anemia of severe B₁₂ deficiency.

Herman Nilsson-Ehle

References

[1]. Hvas AM, Vestergaard H, Gerdes LU, Nexø E. Physicians' use of plasma methylmalonic acid as a diagnostic tool. J Intern Med 2000;247:311-7.

[2]. Hvas AM, Lous J, Ellegaard J, Nexø E. Diagnosis of vitamin B-12 deficiency in general practice. Submitted 2001.

[3]. Hvas AM, Ellegaard J, Nexø E. Increased plasma methylmalonic acid level does not predict clinical manifestations of vitamin B12 deficiency. Arch Intern Med 2001;161:1534-41.

[4]. Hvas AM, Juul S, Gerdes LU, Nexø E. The marker of cobalamin deficiency, plasma methylmalonic acid, correlates to plasma creatinine. J Intern Med 2000;247:507-12.

[5]. Hvas AM, Ellegaard J, Nexø E. Vitamin B12 treatment normalizes metabolic markers but has limited clinical effect: a randomized placebo-controlled study. Clin Chem 2001;47:1396-404.

[6]. Hvas AM, Juul S, Nexø E, Ellegaard J. Vitamin B-12 treatment has limited effect on health related quality of life among individuals with elevated plasma methylmalonic acid: A randomized placebo-controlled study. Submitted 2001.

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Published November 22, 2001