title: An audit of holotranscobalamin ("Active" B12) and methylmalonic acid assays for the assessment of vitamin B12 status: application in a mixed patient population.
abstract: BACKGROUND
  Vitamin B12 insufficiency/deficiency is common in mixed patient populations. However there is no single marker which can reliably diagnose B12 insufficiency/deficiency. Elevated concentrations of methylmalonic acid (MMA) are considered the most representative marker of metabolic vitamin B12 insufficiency, but poor assay availability limits clinical utility. Low concentrations of serum vitamin B12 are often used to assess vitamin B12 status but this approach generates a high rate of false negative results. Emerging evidence indicates that holotranscobalamin (holoTC) may be a more reliable indicator of vitamin B12 status.
  
  
  OBJECTIVE
  We substituted serum vitamin B12 measurement with holoTC, supported by MMA in patients referred for assessment of vitamin B12 status. A service evaluation was undertaken of the pattern of MMA values obtained for patients with holoTC 25-50 pmol/L (an indeterminate result). MMA cut-offs of 280 and 360 nmol/L were applied for patients ≤ 65 or >65 years respectively.
  
  
  RESULTS
  A total of 4,175 consecutive patients were investigated and MMA was analysed for 19% of patients. The incidence of elevated MMA was 41% (holoTC, 25-29 pmol/L), 32% (30-34 pmol/L), 33% (35-39 pmol/L), 30% (40-44 pmol/L), and 26% (45-50 pmol/L).
  
  
  CONCLUSIONS
  Our results indicate that in the clinical setting a holoTC between 25 and 50 pmol/L is a poor predictor for the concentration of MMA provided the goal is to identify patients with MMA values above the limits used in the present study. Further studies are needed to evaluate to what extent holoTC <25 and >50 pmol/L reflect circulatory MMA concentrations.
authors: The Nutristasis Unit, GSTS Pathology (part of King's Healthcare Partners), St. Thomas' Hospital, London, UK. Electronic address: agata.malefora@gsts.com.
authors: Agata
authors: A
authors: Sobczyńska-Malefora
authors: The Nutristasis Unit, GSTS Pathology (part of King's Healthcare Partners), St. Thomas' Hospital, London, UK.
authors: Renata
authors: R
authors: Gorska
authors: The Nutristasis Unit, GSTS Pathology (part of King's Healthcare Partners), St. Thomas' Hospital, London, UK.
authors: Michel
authors: M
authors: Pelisser
authors: The Nutristasis Unit, GSTS Pathology (part of King's Healthcare Partners), St. Thomas' Hospital, London, UK.
authors: Patricia
authors: P
authors: Ruwona
authors: Laboratory Informatics, GSTS Pathology (part of King's Healthcare Partners), St. Thomas' Hospital, London, UK.
authors: Bernie
authors: B
authors: Witchlow
authors: The Nutristasis Unit, GSTS Pathology (part of King's Healthcare Partners), St. Thomas' Hospital, London, UK.
authors: Dominic J
authors: DJ
authors: Harrington
mesh_terms: D015415:Biomarkers / Q000097:blood; D006801:Humans; D008764:Methylmalonic Acid / Q000032:analysis*; D014155:Transcobalamins / Q000032:analysis*; D014805:Vitamin B 12 / Q000097:blood*
chemical_list: D015415:Biomarkers; D014155:Transcobalamins; D008764:Methylmalonic Acid; D014805:Vitamin B 12
keywords: Holotranscobalamin; Methylmalonic acid; Reference ranges; Renal function; Vitamin B(12); “Active” vitamin B(12)