Klee GG

Magera MJ

Matchar DB

Moller J

Rasmussen K

English

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External quality assessment of urinary methylmalonic acid quantification – results of a pilot study

Vogeser, Michael

Müller, Wilhelm

Lorenzl, Stefan

Open Access LMU ( Ludwig-Maximilians-Univ. München)

Clin Chem Lab Med 2007;45(5):695–696  2007 by Walter de Gruyter • Berlin • New York. DOI 10.1515/CCLM.2007.109 2006/520Article in press - uncorrected proofLetter to the EditorExternal quality assessment of urinary methylmalonic acidquantification – results of a pilot studyTable 1 Descriptive statistics for urinary methylmalonicacid (MMA) results for ten laboratories observed for fourstudy samples.Sample MMA, mmol/mol creatinine CV, %IDMean SD Min MaxA 13.0 1.2 9.6 15.5 9.1B 0.8 0.3 0.5 1.4 44.2C 5.1 1.1 2.9 6.9 21.0D 30.0 6.0 19.2 44.7 20.1Michael Vogeser1,*, Wilhelm Mu¨ller2 andStefan Lorenzl31 Institute of Clinical Chemistry, Hospital of theUniversity of Munich, Munich, Gemany2 Chromsystems GmbH, Munich, Germany3 Clinic of Neurology, Hospital of the University ofMunich, Munich, GermanyKeywords: cobalamin deficiency; EQA; methylmalo-nic acid; urine.Measurement of methylmalonic acid (MMA) is recog-nised as a useful tool in the diagnostic work-up ofsuspected cobalamin deficiency (1). Increased con-centrations of MMA in both serum and urine areindicative of cobalamin deficiency at the tissue level.MMA measurement in serum as the sample materialis convenient from a logistic point of view, since ana-lysis can be performed using residual sample materialafter serum cobalamin measurement requested as ascreening test. The major drawbacks of serum MMAmeasurement, however, are the impact of impairedrenal function leading to high MMA concentrations,irrespective of individual cobalamin status (2), and thetypically very low concentration range of MMA inserum samples. In urine, far higher concentrations ofMMA are present compared to serum, facilitatinganalyses. Furthermore, calculation of the MMA/crea-tinine ratio can compensate impaired MMA excretionin renal failure.While external quality assessment programs forserum MMA quantification have been implemented(3), no corresponding services are available for urin-ary MMA measurement so far, and no commercialmaterials for assay calibration and quality control areavailable. In the January 2006 issue of Clinical Chem-istry and Laboratory Medicine, we announced a pilotstudy on external quality assessment of urinary MMAmeasurement and invited laboratories to participatein this investigation. In response to this announce-ment, a total of ten European laboratories requestedtest samples, and lyophilised aliquots of four studysamples were shipped. These samples were manu-factured (Chromsystems GmbH, Munich, Germany)by spiking a native urine sample from a healthy vol-unteer (sample B) with different quantities of a pure*Corresponding author: Michael Vogeser, Institute ofClinical Chemistry, Hospital of the University of Munich,Marchioninistr. 15, 81377 Munich, GermanyPhone: q49-89-70953221, Fax: q49-89-70953240,E-mail: michael.vogeser@med.uni-muenchen.deaqueous solution of methylmalonic acid (Aldrich,Taufkirchen, Germany; catalogue no. M5,405-8, Lot32174-494); the calculated increase in MMA concen-trations in the spiked samples was q3 mg/L (sampleC), q9 mg/L (sample A), and q20 mg/L (sample D).The creatinine concentration of the samples was0.57 g/L (Jaffe).Results expressed as mmol MMA per mol crea-tinine were reported up to June 2006 by the par-ticipants (conversion of units: wmmol/mol crea-tininex=1.04™wmg/g creatininex). Analysis of MMAwas carried out by gas chromatography-mass spec-trometry in nine laboratories, and by liquid chroma-tography-tandem mass spectrometry in the remain-ing laboratory.Mean creatinine-related urinary MMA concentra-tions reported for the four study samples are given inTable 1, together with the respective inter-laboratorycoefficients of variation. All of the results are shownin Figure 1. The upper limit of the reference range forurinary MMA reported in different studies varies from3.5 to 5.1 mg/g creatinine (4–7). The intraindividualvariation of urinary MMA excretion in non-cobalamin-deficient individuals can be substantial, with coeffi-cients of variation of approximately 30% (8).For each result reported by the participants – incor-porating the inaccuracy of MMA and creatinine quan-tification – the relative deviation from the mean forall results reported for each sample was calculated.This deviation was )20% in 12 of the total 40 meas-urements (30%). Four laboratories reported resultswith less than 20% deviation for all four samples; twolaboratories reported results with less than 20% devi-ation for three of the four samples. Two further lab-oratories reported results with less than 20%deviation for two of the four samples. Among theresults for all samples, three had a deviation of morethan 20% in one laboratory, and in one laboratory thedeviation for all four samples was )20%.Our data suggest that in a sample of ten Europeanclinical laboratories, urine with normal MMA concen-trations (in relation to preliminary reference ranges)Bereitgestellt von | Universitaetsbibliothek der LMU MuenchenAngemeldet | 129.187.254.47Heruntergeladen am | 18.11.13 10:54696 Vogeser et al.: Quality assessment of urinary MMA quantificationArticle in press - uncorrected proofFigure 1 Individual urinary methylmalonic acid results reported from ten laboratories for four study samples.Sample A, rhomboids; sample B, squares; sample C, circles; sample D, triangles. Horizontal lines indicate the mean concen-tration reported for the four samples.was correctly distinguished from urine with MMAconcentrations typically found in cobalamin deficien-cy. However, the interlaboratory coefficients of vari-ation observed in our investigation (approx. 20% atthe decision concentration level) are higher than typ-ically found in proficiency testing programs for stan-dard analytes and a deviation of)20% from themeanconcentration for samples was observed in a substan-tial proportion of measurements. Improvement ininterlaboratory agreement of urinary MMA measure-ment might be achieved if materials for calibrationand routine quality control of urinary MMA measure-ment become commercially available in the future.In summary, our study has demonstrated thenecessity of implementing quality assurance systemsfor urinary MMA measurement and the feasibility ofan interlaboratory survey using lyophilised samplesfor this analyte was demonstrated. Implementation ofa proficiency testing scheme for urinary MMA meas-urement in the future might be performed in accor-dance with the Guidelines of the European Co-operation for Accreditation (EA) (9).AcknowledgementsThe study was supported by the Hans-Fischer-Gesellschaft,Munich, Germany.References1. Klee GG. Cobalamin and folate evaluation: measurementof methylmalonic acid and homocysteine vs. vitaminB(12) and folate. Clin Chem 2000;46:1277–83.2. Lindgren A. Elevated serum methylmalonic acid. Howmuch comes from cobalamin deficiency and how muchcomes from the kidneys? Scand J Clin Lab Invest 2002;62:15–20.3. Moller J, Rasmussen K, Christensen L. External qualityassessment of methylmalonic acid and total homocys-teine. Clin Chem 1999;45:1536–42.4. Marcell PD, Stabler SP, Podell ER, Allen RH. Quantitationof methylmalonic acid and other dicarboxylic acids in nor-mal serum and urine using capillary gas chromatography-mass spectrometry. Anal Biochem 1985;150:58–66.5. Matchar DB, Feussner JR, Millington DS, Wilkinson RH Jr,Watson DJ, Gale D. Isotope-dilution assay for urinarymethylmalonic acid in the diagnosis of vitamin B12 defi-ciency. A prospective clinical evaluation. Ann Intern Med1987;106:707–10.6. Rasmussen K, Nathan E. The clinical evaluation of cobal-amin deficiency by determination of methylmalonic acidin serum or urine is not invalidated by the presence ofheterozygous methylmalonic-acidaemia. J Clin Chem ClinBiochem 1990;28:419–21.7. Magera MJ, Helgeson JK, Matern D, Rinaldo P. Methyl-malonic acid measured in plasma and urine by stable-iso-tope dilution and electrospray tandem mass spectro-metry. Clin Chem 2000;46:1804–10.8. Rasmussen K, Moller J, Ostergaard K, Kristensen MO,Jensen J. Methylmalonic acid concentrations in serum ofnormal subjects: biological variability and effect of oral L-isoleucine loads before and after intramuscular adminis-tration of cobalamin. Clin Chem 1990;36:1295–9.9. EA, European Co-operation for Accreditation: The ILACG13 Guidelines for the Requirements for the Competenceof Providers of Proficiency Testing Schemes. www.european-accreditation.org/Docs/0003_International/0001_ILAC/00500_ILAC%20G13%202000.pdf.Bereitgestellt von | Universitaetsbibliothek der LMU MuenchenAngemeldet | 129.187.254.47Heruntergeladen am | 18.11.13 10:54

Co-operation for Accreditation: The ILAC G13 Guidelines for the Requirements for the Competence of Providers of Proficiency Testing Schemes.

Cobalamin and folate evaluation: measurement of methylmalonic acid and homocysteine vs. vitamin B(12) and folate.

Elevated serum methylmalonic acid. How much comes from cobalamin deficiency and how much comes from the kidneys? Scand J Clin Lab Invest

External quality assessment of methylmalonic acid and total homocysteine. Clin Chem 1999;45:1536–42.

Isotope-dilution assay for urinary methylmalonic acid in the diagnosis of vitamin B12 deficiency. A prospective clinical evaluation.

Methylmalonic acid concentrations in serum of normal subjects: biological variability and effect of oral Lisoleucine loads before and after intramuscular administration of cobalamin.

Methylmalonic acid measured in plasma and urine by stable-isotope dilution and electrospray tandem mass spectrometry. Clin Chem

Quantitation of methylmalonic acid and other dicarboxylic acids in normal serum and urine using capillary gas chromatographymass spectrometry. Anal Biochem

The clinical evaluation of cobalamin deficiency by determination of methylmalonic acid in serum or urine is not invalidated by the presence of heterozygous methylmalonic-acidaemia.

External quality assessment of urinary methylmalonic acid quantification - results of a pilot study

Universität München: Elektronischen Publikationen

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External quality assessment of urinary methylmalonic acid quantification - results of a pilot study

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