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[Cobalamin deficiency despite normal serum cobalamins].

K Rasmussen1, K O Pedersen, S Sillesen

  • 1Arhus Kommunehospital, klinisk-kemisk afdeling.

Ugeskrift for Laeger
|February 3, 1992
PubMed
Summary
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Elevated methylmalonic acid indicates functional cobalamin deficiency, even with normal serum cobalamin levels. Vitamin B12 supplementation normalized levels, confirming the diagnosis.

Area of Science:

  • Biochemistry
  • Clinical Medicine
  • Nutritional Science

Background:

  • Cobalamin (vitamin B12) deficiency can cause serious neurological and hematological issues.
  • Serum cobalamin levels are commonly used to diagnose deficiency, but can be misleading.

Observation:

  • A 77-year-old male presented with normal serum cobalamin concentrations but elevated serum methylmalonic acid (MMA) levels.
  • Two different assay methods confirmed the normal cobalamin and elevated MMA concentrations.

Findings:

  • Functional cobalamin deficiency was diagnosed based on elevated serum MMA.
  • Vitamin B12 supplementation normalized the patient's serum MMA levels, confirming the diagnosis.

Implications:

  • Normal serum cobalamin levels should not rule out cobalamin deficiency.

Related Experiment Videos

  • Measuring serum methylmalonic acid is a crucial, sensitive, and specific test for diagnosing cobalamin deficiency.
  • Clinicians should consider MMA testing in suspected cases of cobalamin deficiency to avoid misdiagnosis.