Course Authors

Robert G. Lerner, M.D.

In the past three years, Dr. Lerner has been a speaker for Aventis, Novo Nordisk and Pharmacia.

Estimated course time: 1 hour(s).

Albert Einstein College of Medicine – Montefiore Medical Center designates this enduring material activity for a maximum of 1.0 AMA PRA Category 1 Credit(s)™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.

In support of improving patient care, this activity has been planned and implemented by Albert Einstein College of Medicine-Montefiore Medical Center and InterMDnet. Albert Einstein College of Medicine – Montefiore Medical Center is jointly accredited by the Accreditation Council for Continuing Medical Education (ACCME), the Accreditation Council for Pharmacy Education (ACPE), and the American Nurses Credentialing Center (ANCC), to provide continuing education for the healthcare team.

 

Learning Objectives

Upon completion of this Cyberounds^®, you should be able to:

• Discuss the controversy about vitamin B₁₂ and folate dietary supplementation and knowledgeably prescribe appropriately

• Interpret laboratory reports of vitamin B₁₂ and homocysteine blood levels

• Appreciate defects of vitamin B₁₂ absorption other than classic pernicious anemia.

 

When a patient presents with classic pernicious anemia, the diagnosis and treatment choice are straightforward. A typical patient might present complaining of fatigue. A routine CBC would reveal a macrocytic anemia. An assay of the serum vitamin B₁₂ level would be in the low range, unequivocally. A confirmatory test of anti-intrinsic factor antibody or a Schilling test would be clearly abnormal. If the patient were fortunate, there would be no neurological abnormality. Subsequent treatment with vitamin B₁₂ injections, starting with a loading dose of 1000 mg daily for a week followed by lifelong injections of 1000 mg monthly, would return the blood count to normal and the patient would remain well.

However, things are not always that simple. Vitamin B₁₂ absorption is very complex and deficiency can be caused by mechanisms other than the typical picture of an autoimmune disease leading to a deficiency of intrinsic factor. For example, any defect that interferes with the normal mechanism of absorption and transport can produce a vitamin B₁₂ deficiency. Food, containing bound vitamin B₁₂ is acted upon in the stomach by acid and pepsin releasing free vitamin. If pharmacologic vitamin B₁₂ is ingested, it is already free vitamin when it arrives in the stomach. The free vitamin is bound to binding protein found in the gastric juice (R binder or haptocorrin). The haptocorrin bound vitamin is digested free of its binder in the small bowel so that it is available to bind once again, this time to intrinsic factor which was secreted by the stomach. The intrinsic factor-vitamin B₁₂ complex binds to a receptor in the mucosa of the ileum and is released from the intrinsic factor and transported into the circulation where it is once again bound to a transport protein and delivered to the tissues.

An additional diagnostic complication is that current techniques used to determine serum vitamin B₁₂ levels measure "total vitamin B₁₂," which includes the physiologic vitamin B₁₂-transcobalamin complex as well as vitamin B₁₂ bound to haptocorrin and other factors. The result is that there is considerable overlap between normal and low levels.

This overlap could lead to confusion and delay in making a proper diagnosis in a patient presenting with a classic macrocytic anemia and a megaloblastic bone marrow. It is likely, however, that the proper diagnosis for a patient with these clinical manifestations would soon be evident. Perhaps more important is the possibility that a missed diagnosis of vitamin B₁₂ deficiency, and the failure to treat, will provoke serious permanent neurologic damage.

In this Cyberounds^®, we focus on two illustrative cases -- one actual, one hypothetical -- which, hopefully, will help raise the diagnostic suspicion for vitamin B₁₂ deficiency and illuminate the clinical relevance of the metabolite, homocysteine.

Case 1

A 72-year-old woman from New York has been receiving vitamin B₁₂ injections on a regular basis from her primary care physician because of the belief that they make her feel good. She then retires to Florida but does not continue the vitamin B₁₂ injections and continues to feel well. Five years later, she develops leg weakness and sees a new physician. A provisional diagnosis of spinal stenosis is made and she is referred for physical therapy. Despite some initial improvement with physical therapy, she gets worse insidiously. Physical examination reveals some leg weakness, as well as absent ankle jerk and knee jerk reflexes. Laboratory data reveal a normal CBC and urine analysis. A comprehensive metabolic profile is normal except for a borderline elevation of glucose.

Q. Does the normal CBC rule out pernicious anemia and vitamin B₁₂ deficiency?

A. She certainly is not anemic, but she may be deficient in vitamin B₁₂. If she is deficient in vitamin B₁₂, the mechanism could be classic lack of intrinsic factor or it could result from another mechanism.

Q. Should the vitamin B₁₂ level be measured even if she is not anemic?

A. Yes. The vitamin B₁₂ level would be an important part of the evaluation of a patient with her neurologic complaints even if no anemia is present. The vitamin B₁₂ level was measured and was 250pmol/L. The normal range reported from this laboratory is 200 to 900pmol/L.

Q. Since her reported vitamin B₁₂ level was in the normal range, can we assume that she is not vitamin B₁₂ deficient?

A. No. As mentioned earlier, there is considerable overlap between low and normal levels of vitamin B₁₂. Levels of 200 to 300 pmol/L are in this gray area and are not definitive.

Q. How can it be determined if the level of 250 is normal or low?

A. One technique is to assay the metabolites homocysteine and methylmalonic acid. The blood level of homocysteine is increased by deficiencies of either vitamin B₁₂ or folic acid, while the blood level or urinary excretion of methylmalonic acid is, usually, only increased by vitamin B₁₂ deficiency. If the levels of both metabolites are normal, the clinician can reasonably assume that the "gray area" vitamin B₁₂ blood level for this patient is actually normal since there is no metabolic effect indicating a physiologic deficiency.

If the homocysteine and methylmalonic acid levels are increased, and there is no other metabolic explanation (such as renal disease) for the increase, then the implication is that the "gray area" vitamin B₁₂ level is actually low. Alternatively, an assay for anti-intrinsic factor antibody could be done. A normal test would not help, but if an antibody were present it would make the diagnosis of pernicious anemia. Finally, it is also possible to make the diagnosis by measuring how much vitamin B₁₂ is bound physiologically to the protein transcobalamin. However, this assay is not commercially available.

In this patient, no anti-intrinsic factor antibody was present but the homocysteine level was increased to 25 micromol/L (normal <15 in this laboratory) and the methylmalonate was increased to 235 ng/ml (normal 19 to 76 ng/ml in this laboratory). Accordingly, she was started on vitamin B₁₂ injections once again and her condition remained stable.

Q. If she remained stable, what was so important about diagnosing her vitamin B₁₂ deficiency?

A. A key point: this woman probably has two disorders, i.e., both spinal stenosis and vitamin B₁₂ deficiency. Much has been made in the literature about the falsely normal serum B₁₂ level. In truth, in most cases, where someone has normal B₁₂ levels, yet is B₁₂-deficient, there is no clinical consequence. In other words, the patient is neither anemic nor neurologically abnormal. Lindenbaum et al. looking only at patients with neuropsychiatric symptoms due to vitamin B₁₂ deficiency found that only 40 out of 141 (28%) had no anemia or macrocytosis and only 19 had both normal hemoglobin and hematocrit.(1)

Since most patients with neurologic symptoms from vitamin B₁₂ deficiency actually are anemic, this woman might not experience improvement in her neurologic function. It is true that if she received no vitamin B₁₂ treatment she might insidiously develop further neurologic damage, perhaps permanently. However, in this case, the impairment of neurologic function is very likely caused by her spinal stenosis or other conditions and there might be no recovery of neurologic function because of vitamin B₁₂ treatment.

Q. Did this woman have pernicious anemia or some other reason for vitamin B₁₂ deficiency?

A. The data provided so far do not answer that question. If there were proof that she lacked intrinsic factor, then the diagnosis would be established. Proof could be provided by a positive test for anti-intrinsic factor antibody or by an abnormal Schilling test.

The Schilling test is done in two parts. First, absorption of oral vitamin B₁₂ is tested. Then, if the absorption is abnormal, the test is repeated along with the oral administration of intrinsic factor. If the oral intrinsic factor corrects the absorption defect, the diagnosis of pernicious anemia is confirmed.

There are, however, problems with the Schilling test. First, it is often not available locally. Second, the crystalline vitamin B₁₂ given orally bypasses the need for acid-protease release of the vitamin from its binding to food. Third, the test, even using food bound vitamin B₁₂, is not as sensitive as the biochemical markers of methylmalonic acid and homocysteine. Therefore, a normal Schilling test might still be consistent with pernicious anemia or might mean that this patient has a different basis for vitamin B₁₂ deficiency such as deficiency of gastric proteases or inadequate oral intake.

Case 2

A 65-yearold man in his usual state of good health asks his primary care physician to check his homocysteine level and C-reactive protein level because he read in the lay press that they are risk factors for coronary artery disease. The homocysteine level is reported by a major national laboratory to be abnormally high at 12.5 micromol/L. The report indicates the "Reference Range" as "<10.4 micromol/L."

Q. Does this patient have an abnormally high homocysteine level?

A. Unfortunately, the answer is not simple. Even the appropriate values to be used for "normal" or "reference range," or how to use the value for determining whether a patient has a vitamin B₁₂ deficiency, folate deficiency, hypercoagulable state or risk factor for arterial disease, are sometimes unclear. According to the testing company, the reference range referred to above (10.4 micromol/L) was chosen as a target level based upon National Health and Nutrition Examination Survey III data that demonstrated an increased risk of cardiovascular disease in patients with high levels of homocysteine. However, published articles based on that data set reported a 2.4 fold increase in history of heart attack or stroke with a level of >12 micromol/L.(2)

The position statement of the American Society of Human Genetics/American College of Medical Genetics Test and Technology Transfer Committee Working Group defines an elevated homocysteine as >15 micromol/L while stating that there may also be graded increased risks for persons with concentration 10-15 micromol/L.(3) This 65-year-old man actually has a level that falls within 2 standard deviations of the mean and is not suggestive of vitamin B₁₂ deficiency or folate deficiency despite the fact that it was reported as abnormally high.

Johan B. Ubbink suggests that a reference range based upon a mean and a 95% confidence interval is not equal to desirable homocysteine levels in population groups with suboptimal vitamin status.(4) He further questions whether a desirable plasma homocysteine concentration below 9 micromol/L is attainable for most people in the general population.(5)

Q. Should the patient's physician recommend that he receive vitamin supplements including vitamin B₁₂?

A. The answer is controversial. A study reported in The New England Journal of Medicine concluded that treatment with a combination of folic acid, vitamin B₁₂ and pyridoxine significantly reduces homocysteine levels (from a mean of 11.1 to a mean of 7.2), and decreases the rate of restenosis and the need for revascularization of the target lesion after coronary angioplasty. The authors recommended that this inexpensive treatment, which has minimal side effects, should be considered as adjunctive therapy for patients undergoing coronary angioplasty.(6)

Willet and Stampfer conclude that the consequences of marginal vitamin B₁₂ status remain unclear, but they may include increased risks of vascular disease and cancer. They go on to state that crystalline vitamin B₁₂, the form that is used in supplements, does not require gastric acid for absorption, so a multivitamin can ensure that intake is adequate for mostpeople.(7)

Q. Can vitamin B₁₂ or folate supplementation cause harm?

Q. It has been well-known for years that folic acid supplementation in large doses can reverse the anemia of vitamin B₁₂ and mask its deficiency. This would allow the insidious onset of neuropsychiatric symptoms. Dickinson has concluded that the hypothetical and avoidable side-effects of fortification with folic acid have to be balanced against the certain benefit and concludes that this possibility can readily be overcome by adequate education of doctors.(8)

Physicians should be on the alert for neurologic symptoms and consider vitamin B₁₂ deficiency, especially if the patient is receiving folate supplementation. An illustrative case of a woman with sickle cell anemia receiving folate supplementation and developing severe neuro-psychiatric symptoms due to overlooked vitamin B₁₂ deficiency has just been published.(9)

Some authors have suggested that the results of homocysteine lowering studies in coronary intervention are contradictory and have even identified potential mechanisms by which these interventions might stimulate myointimal hyperplasia.(10)

However, overall, homocysteine lowering therapy appears to have a beneficial effect on restenosis even after percutaneous coronary intervention for narrowings in small coronary arteries.(11)