Schilling test: physiologic basis for and use as a diagnostic test

Effects of oral crystalline cyanocobalamin 1000 μg/d in the treatment of pernicious anemia: An open-label, prospective study in Ten Patients

BACKGROUND

Standard treatment of cobalamin (vitamin B12) deficiency involvesregular (1000 μg/mo) IM cyanocobalamin administration. It has been suggested that high-dose (>2000 μg/d) oral cyanocobalamin may be effective in patients with pernicious anemia.

OBJECTIVE

The aim of this study was to assess the efficacy and tolerability of oral crystalline cyanocobalamin 1000 μg/d in patients with cobalamin deficiency related to established pernicious anemia.

METHODS

This open-label, prospective study was conducted at StrasbourgUniversity Hospital, Strasbourg, France. Patients aged ≥18 years with well-documented cobalamin deficiency related to pernicious anemia were enrolled. Patients received crystalline cyanocobalamin 1000 μg QD PO (capsule) for at least 3 months. Serum cobalamin, folate, iron, and homocysteine concentrations were measured, and a complete blood count was obtained, before (month 0; baseline) and after treatment.

RESULTS

Ten patients (7 women, 3 men; mean [SD] age, 72.1 [15.5] years) entered the study. After 3 months of treatment, serum cobalamin concentration increased in all 9 patients in whom it was measured (mean [SD] increase, 117.4 [30.8] pg/mL; P < 0.001 vs baseline). Serum cobalamin concentrations were normalized (>200 pg/mL) in 6 patients. The serum cobalamin concentration was unavailable in 1 patient because of technical problems. Eight patients had increased hemoglobin concentrations (mean [SD] increase, 2.5 [2.4] g/dL; P < 0.01 vs baseline). All 10 patients had decreased mean erythrocyte corpuscular volumes (mean [SD] decrease, 10.4 [6.2] fL; P < 0.003 vs baseline). Four patients received concomitant blood transfusions or folate and iron supplementation. Three patients experienced clinical improvement in paresthesia, reflex abolition, or combined medullary sclerosis (each, 1 patient).

CONCLUSION

The results of this small study in patients with cobalamin deficiencyrelated to pernicious anemia suggest that oral crystalline cyanocobalamin 1000 μg/d may be an effective treatment.

Cobalamin deficiency

Cobalamin (Cbl, vitamin B12) consists of a corrinoid structure with cobalt in the centre of the molecule. Neither humans nor animals are able to synthesize this vitamin. Foods of animal source are the only natural source of cobalamin in human diet. There are only two enzymatic reactions in mammalian cells that require cobalamin as cofactor. Methylcobolamin is a cofactor for methionine synthase. The enzyme methylmalonyl-CoA-mutase requires adenosylcobalamin as a cofactor. Therefore, serum concentrations of homocysteine (tHcy) and methylmalonic acid (MMA) will increase in cobalamin deficiency. The cobalamin absorption from diet is a complex process that involves different proteins: haptocorrin, intrinsic factor and transcobalamin (TC). Cobalamin that is bound to TC is called holotranscobalamin (holoTC) which is the metabolically active vitamin B12 fraction. HoloTC consists 6 and 20% of total cobalamin whereas 80% of total serum cobalamin is bound to another binding protein, haptocorrin. Cobalamin deficiency is common worldwide. Cobalamin malabsorption is common in elderly subjects which might explain low vitamin status. Subjects who ingest low amount of cobalamin like vegetarians develop vitamin deficiency. No single parameter can be used to diagnose cobalamin deficiency. Total serum cobalamin is neither sensitive nor it is specific for cobalamin deficiency. This might explain why many deficient subjects would be overlooked by utilizing total cobalamin as status marker. Concentration of holotranscobalamin (holoTC) in serum is an earlier marker that becomes decreased before total serum cobalamin. Concentrations of MMA and tHcy increase in blood of cobalamin deficient subjects. Despite limitations of these markers in patients with renal dysfunction, concentrations of MMA and tHcy are useful functional markers of cobalamin status. The combined use of holoTC and MMA assays may better indicate cobalamin status than either of them. Because Cbl deficiency is a risk factor for neurodegenerative diseases an early diagnosis of a low B12 status is required which should be followed by an effective treatment in order to prevent irreversible damages.

Holo-Transcobalamin Is an Early Marker of Changes in Cobalamin Homeostasis. A Randomized Placebo-controlled Study

Background: We examined the effect of oral vitamin B12 treatment on fluctuations in plasma total cobalamin and its binding proteins transcobalamin (TC) and haptocorrin (HC).

Methods: Patients (n = 88; age range, 38–80 years) undergoing coronary angiography (part of the homocysteine-lowering Western Norway B-Vitamin Intervention Trial) were allocated to daily oral treatment with (a) vitamin B12 (0.4 mg), folic acid (0.8 mg), and vitamin B6 (40 mg); (b) vitamin B12 and folic acid; (c) vitamin B6; or (d) placebo. EDTA blood was obtained before treatment and 3, 14, 28, and 84 days thereafter.

Results: The intraindividual variation for patients not treated with B12 was ∼10% for plasma total cobalamin, total TC, apo-TC, and apo-HC, and &lt;20% for holo-TC and TC saturation. In B12-treated patients, the maximum change in concentrations was observed already after 3 days for total TC (−16%), holo-TC (+54%), and TC saturation (+82%). At this time holo-HC (+20%) and plasma total cobalamin (+28%) showed an initial burst, but had increased further at 84 days. All changes were highly significant compared with the control group (P &lt;0.0001).

Conclusions: Oral vitamin B12 treatment produces maximal effects on total TC, holo-TC, and TC saturation within 3 days, whereas maximal increases in holo-HC and plasma total cobalamin occur later. The results support the view that holo-TC is an early marker of changes in cobalamin homeostasis.

Biochemical tests in diseases of the intestinal tract: their contributions to diagnosis, management, and understanding the pathophysiology of specific disease states

Biochemical testing plays a major role in the complete evaluation of patients with suspected or established intestinal disease. We have classified these tests according to the medium in which they are performed: breath tests, including isotopic and nonisotopic tests, fecal tests, urine tests, serum tests, tissue tests, and other tests. The principles of various tests are outlined, and the role of each test in the evaluation of particular gastrointestinal disorders is discussed.