BACKGROUND: Conventional tests for vitamin B(12) deficiency measure total serum vitamin B12, whereas only that portion of vitamin B12 carried by transcobalamin (holotranscobalamin) is metabolically active. Measurement of holotranscobalamin (holoTC) may be more diagnostically accurate for detecting B(12) deficiency that requires therapy. We developed an automated assay for holoTC that can be used on the Abbott AxSYM immunoassay analyzer. METHODS: AxSYM Active B12 is a 2-step sandwich microparticle enzyme immunoassay. In step 1, a holoTC-specific antibody immobilized onto latex microparticles captures holoTC in samples of serum or plasma. In step 2, the captured holoTC is detected with a conjugate of alkaline phosphatase and antiTC antibody. RESULTS: Neither apoTC nor haptocorrin exhibited detectable cross-reactivity. The detection limit was < or = 0.1 pmol/L. Within-run and total imprecision (CV ranges) were 3.4%-5.1% and 6.3%-8.5%, respectively. Assay CVs were < 20% from at least 3 pmol/L to 107 pmol/L. With diluted serum samples, measured concentrations were 104%-114% of the expected values in the working range of the assay. No interference from bilirubin, hemoglobin, triglycerides, erythrocytes, rheumatoid factor, or total protein was detected at expected (abnormal) concentrations. A comparison of the AxSYM Active B12 assay with a commercial RIA for holoTC yielded the regression equation: AxSYM = 0.98RIA + 4.7 pmol/L (S(y x), 11.4 pmol/L; n = 204). Assay throughput was 45 tests/h. A 95% reference interval of 19-134 pmol/L holoTC was established with samples from 292 healthy individuals. CONCLUSIONS: The AxSYM Active B12 assay allows rapid, precise, sensitive, specific, and automated measurement of human holoTC in serum and plasma.
BACKGROUND: Conventional tests for vitamin B(12) deficiency measure total serum vitamin B12, whereas only that portion of vitamin B12 carried by transcobalamin (holotranscobalamin) is metabolically active. Measurement of holotranscobalamin (holoTC) may be more diagnostically accurate for detecting B(12) deficiency that requires therapy. We developed an automated assay for holoTC that can be used on the Abbott AxSYM immunoassay analyzer. METHODS: AxSYM Active B12 is a 2-step sandwich microparticle enzyme immunoassay. In step 1, a holoTC-specific antibody immobilized onto latex microparticles captures holoTC in samples of serum or plasma. In step 2, the captured holoTC is detected with a conjugate of alkaline phosphatase and antiTC antibody. RESULTS: Neither apoTC nor haptocorrin exhibited detectable cross-reactivity. The detection limit was < or = 0.1 pmol/L. Within-run and total imprecision (CV ranges) were 3.4%-5.1% and 6.3%-8.5%, respectively. Assay CVs were < 20% from at least 3 pmol/L to 107 pmol/L. With diluted serum samples, measured concentrations were 104%-114% of the expected values in the working range of the assay. No interference from bilirubin, hemoglobin, triglycerides, erythrocytes, rheumatoid factor, or total protein was detected at expected (abnormal) concentrations. A comparison of the AxSYM Active B12 assay with a commercial RIA for holoTC yielded the regression equation: AxSYM = 0.98RIA + 4.7 pmol/L (S(y x), 11.4 pmol/L; n = 204). Assay throughput was 45 tests/h. A 95% reference interval of 19-134 pmol/L holoTC was established with samples from 292 healthy individuals. CONCLUSIONS: The AxSYM Active B12 assay allows rapid, precise, sensitive, specific, and automated measurement of human holoTC in serum and plasma.
Authors: E Laird; M C Casey; M Ward; L Hoey; C F Hughes; K McCarroll; C Cunningham; J J Strain; H McNulty; A M Molloy Journal: J Nutr Health Aging Date: 2017 Impact factor: 4.075
Authors: C Lewerin; H Nilsson-Ehle; S Jacobsson; H Johansson; V Sundh; M K Karlsson; Ö Ljunggren; M Lorentzon; J A Kanis; U H Lerner; S R Cummings; C Ohlsson; D Mellström Journal: Osteoporos Int Date: 2013-10-16 Impact factor: 4.507
Authors: Rima Obeid; Susanne H Kirsch; Sarah Dilmann; Cosima Klein; Rudolf Eckert; Jürgen Geisel; Wolfgang Herrmann Journal: Eur J Nutr Date: 2015-05-06 Impact factor: 5.614
Authors: James L Mills; Tonia C Carter; John M Scott; James F Troendle; Eileen R Gibney; Barry Shane; Peadar N Kirke; Per M Ueland; Lawrence C Brody; Anne M Molloy Journal: Am J Clin Nutr Date: 2011-06-08 Impact factor: 7.045
Authors: Aneliya Velkova; Jennifer E L Diaz; Faith Pangilinan; Anne M Molloy; James L Mills; Barry Shane; Erica Sanchez; Conal Cunningham; Helene McNulty; Cheryl D Cropp; Joan E Bailey-Wilson; Alexander F Wilson; Lawrence C Brody Journal: Hum Mol Genet Date: 2017-12-15 Impact factor: 6.150
Authors: Anne M Molloy; Faith Pangilinan; James L Mills; Barry Shane; Mary B O'Neill; David M McGaughey; Aneliya Velkova; Hatice Ozel Abaan; Per M Ueland; Helene McNulty; Mary Ward; J J Strain; Conal Cunningham; Miriam Casey; Cheryl D Cropp; Yoonhee Kim; Joan E Bailey-Wilson; Alexander F Wilson; Lawrence C Brody Journal: Am J Hum Genet Date: 2016-04-28 Impact factor: 11.025