title: Suitability of methylmalonic acid and total homocysteine analysis in dried bloodspots.
abstract: Methylmalonic acid (MMA) and total homocysteine (tHCYS) concentrations are used to detect acquired and inborn errors of cobalamin (vitamin B12, Cbl) metabolism and to evaluate the effect of therapeutic interventions. Dried blood spot sampling offers a patient-friendly and easy alternative to plasma sampling. However, dried blood spot concentrations are not necessarily equal to plasma concentrations. Therefore, the objective of this work was to establish the relationship between MMA and tHYS dried blood spot and plasma concentrations to facilitate clinical implementation of dried blood spot sampling. MMA and tHCYS in both plasma and DBS were validated on ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). While position of the punch (in DBS) did affect tHCYS concentration, no influence of hematocrit (Ht) and blood volume on both MMA and tHCYS concentrations was observed. The plasma assay performed better than the DBS assay by most criteria. However, the DBS matrix was superior for tHCYS stability. Paired plasma and DBS samples were obtained from patients suspected for Cbl deficiency and from patients with a known inborn error of metabolism affecting MMA or tHCYS concentration. Based on the strong correlation of tHCYS in both matrices (y=0.46±1.12 (r(2)=0.91)), determination of tHCYS in plasma can be replaced by tHCYS in DBS. However, for MMA, a correlation in the higher (pathological) range of MMA exist, but no correlation was observed in the lower ranges. Therefore the added value of MMA concentrations in DBS is currently unknown and should be further investigated.
authors.affiliation: Department of Medical Genetics, Wilhelmina Children's Hospital, University Medical Centre (UMC) Utrecht, Utrecht, The Netherlands. Electronic address: m.g.desain@umcutrecht.nl.
authors.forename: Monique G M
authors.initials: MGM
authors.lastname: de Sain-van der Velden
authors.affiliation: Department of Medical Genetics, Wilhelmina Children's Hospital, University Medical Centre (UMC) Utrecht, Utrecht, The Netherlands. Electronic address: M.vanderHam-3@umcutrecht.nl.
authors.forename: Maria
authors.initials: M
authors.lastname: van der Ham
authors.affiliation: Department of Medical Genetics, Wilhelmina Children's Hospital, University Medical Centre (UMC) Utrecht, Utrecht, The Netherlands. Electronic address: J.J.M.Jans@umcutrecht.nl.
authors.forename: Judith J
authors.initials: JJ
authors.lastname: Jans
authors.affiliation: Department of Paediatric Gastroenterology and Metabolic Diseases, Wilhelmina Children's Hospital, UMC Utrecht, The Netherlands. Electronic address: G.Visser-4@umcutrecht.nl.
authors.forename: Gepke
authors.initials: G
authors.lastname: Visser
authors.affiliation: Department of Paediatric Gastroenterology and Metabolic Diseases, Wilhelmina Children's Hospital, UMC Utrecht, The Netherlands. Electronic address: P.vanHasselt@umcutrecht.nl.
authors.forename: Peter M
authors.initials: PM
authors.lastname: van Hasselt
authors.affiliation: Department of Medical Genetics, Wilhelmina Children's Hospital, University Medical Centre (UMC) Utrecht, Utrecht, The Netherlands. Electronic address: B.Prinsen@umcutrecht.nl.
authors.forename: Hubertus C M T
authors.initials: HCMT
authors.lastname: Prinsen
authors.affiliation: Department of Medical Genetics, Wilhelmina Children's Hospital, University Medical Centre (UMC) Utrecht, Utrecht, The Netherlands. Electronic address: N.Verhoeven@umcutrecht.nl.
authors.forename: Nanda M
authors.initials: NM
authors.lastname: Verhoeven-Duif
mesh_terms: D001800:Blood Specimen Collection; D002851:Chromatography, High Pressure Liquid; D059788:Dried Blood Spot Testing / Q000379:methods*; D005240:Feasibility Studies; D006710:Homocysteine / Q000096:biosynthesis / Q000097:blood* / Q000378:metabolism; D006801:Humans; D057230:Limit of Detection; D008764:Methylmalonic Acid / Q000097:blood* / Q000378:metabolism; D010949:Plasma / Q000737:chemistry / Q000378:metabolism; D015203:Reproducibility of Results; D012997:Solvents / Q000737:chemistry; D053719:Tandem Mass Spectrometry
chemical_list: D012997:Solvents; D006710:Homocysteine; D008764:Methylmalonic Acid
keywords: Cobalamin; Dried blood spot; Homocysteine; Methylmalonic acid; Ultra performance liquid chromatography–tandem mass spectrometry