Evaluation of a Newly Developed LC-MS/MS Vitamin D Assay
Abstract
Background/Aim: Globally, deficiency of vitamin D is highly prevalent. Besides the known consequences of vitamin D deficiency to bone health, there is now strong evidence that links low vitamin D status to an increase in the risk for diabetes, cancer, cardiovascular disease and autoimmune diseases. It is therefore important to have a highly accurate, reproducible and cost-effective test that is highly predictive of vitamin D status and of diagnostic value. This study was undertaken to validate newly developed high throughput LC-MS/MS 25-hydroxy vitamin D (25(OH)D) assay against current gold standard assays measured at two independent reference laboratories.
Methods: The initial study (n = 40) and follow up study (n = 40) recruited healthy adult men and women volunteers (18 to 55 years old). Vitamin D (25(OH)D) was measured using a targeted LC−MS/MS method.
Results: Unexpectedly, data were not consistent with the values for 25(OH)D obtained from the two independent reference laboratories (as evidenced by correlation coefficients and Bland Altman analyses), although the results between the two reference laboratories were in agreement and highly correlated.
Conclusion: These findings highlight the continued efforts and needs for harmonisation of results and standardisation of analytical methods for 25(OH)D for diagnostic accuracy.
References
Cui A, Zhang T, Xiao P, Fan Z, Wang H, Zhuang Y. Global and regional prevalence of vitamin D deficiency in population-based studies from 2000 to 2022: A pooled analysis of 7.9 million participants. Front Nutr. 2023; 10: 1070808. doi: 10.3389/fnut.2023.1070808.
Meshkin A, Badiee F, Salari N, Hassanabadi M, Khaleghi AA, Mohammadi M. The global prevalence of vitamin D de-ficiency in the elderly: A meta-analysis. Indian J Orthop. 2024;58:223-30. doi: 10.1007/s43465-023-01089-w.
Riccio P. Vitamin D, the sunshine molecule that makes us strong: What does its current global deficiency imply? Nutrients. 2024;16:2015. doi: 10.3390/nu16132015.
Stoica AB, Mărginean C. The impact of vitamin D deficiency on infants' health. Nutrients. 2023 Oct 16;15(20):4379. doi: 10.3390/nu15204379.
Yousef S, Hayawi L, Hossain A, Nahar N, Manuel D, Colman I, et al. Assessment of the quality and content of clinical practice guidelines for vitamin D and for immigrants using the AGREE II instrument: global systematic review. BMJ Open. 2024;14: e080233. doi: 10.1136/bmjopen-2023-080233.
O’Connell TD, Simpson RU. Immunochemical identification of the 1,25-dihydroxyvitamin D3 receptor protein in human heart. Cell Biol Int. 1996;20:621–4. doi: 10.1006/cbir.1996.0081.
Caraba A, Crişan V, Romoşan I, Mozoş I, Murariu M. Vitamin D status, disease activity, and endothelial dysfunction in early rheumatoid arthritis patients. Disease Markers. 2017;2017:5241012. doi: 10.1155/2017/5241012.
Tappia PS, Lopez R, Fitzpatrick-Wong S, Ramjiawan B. Understanding the role of vitamin D in heart failure. Rev Cardiovasc Med. 2023;24:111. doi: 10.31083/j.rcm2404111.
Pires C. Superfoods for type 2 diabetes: A narrative review and proposal for new international recommendations. Medicina. 2023;59:1184. doi: 10.3390/medicina59071184.
Cao M, He C, Gong M, Wu S, He J. The effects of vitamin D on all-cause mortality in different diseases: an evidence-map and umbrella review of 116 randomized controlled trials. Front Nutr. 2023;10:1132528. doi: 10.3389/fnut.2023.1132528.
Bantwal G. A review on vitamin D deficiency and related disorders: What is the right serum vitamin D level? J Assoc Physicians India. 2023;71:11-2. doi: 10.5005/japi-11001-0240.
Md Isa Z, Amsah N, Ahmad N. The impact of vitamin D deficiency and insufficiency on the outcome of type 2 diabetes mellitus patients: A systematic review. Nutrients. 2023;15: 2310. doi: 10.3390/nu15102310.
Al-Oanzi ZH, Alenazy FO, Alhassan HH, Alruwaili Y, Alessa AI, Alfarm NB, et al. The role of vitamin D in reducing the risk of metabolic disturbances that cause cardiovascular diseases. J Cardiovasc Dev Dis. 2023;10:209. doi: 10.3390/jcdd10050209.
Yanping W, Gao X, Cheng Y, Liu M, Liao S, Zhou J, et al. The interaction between obesity and visceral hypersensitivity. J Gastroenterol Hepatol. 2023;38:370-7. doi: 10.1111/jgh.16083.
Di Napoli R, Balzano N, Mascolo A, Cimmino C, Vitiello A, Zovi A, et al. What is the role of nutraceutical products in cancer patients? A systematic review of randomized clinical trials. Nutrients. 2023;15:3249. doi: 10.3390/nu15143249.
Ottaiano A, Facchini S, Santorsola M, Nasti G, Facchini G, Montella L, et al. Circulating vitamin D level and its impact on mortality and recurrence in stage III colorectal cancer patients: A systematic review and meta-analysis. Cancers. 2023;15:3012. doi: 10.3390/cancers15113012.
Kanno K, Akutsu T, Ohdaira H, Suzuki Y, Urashima M. Effect of vitamin D supplements on relapse or death in a p53-immunoreactive subgroup with digestive tract cancer: post hoc analysis of the AMATERASU randomized clinical trial. JAMA Netw Open. 2023;6:e2328886. doi: 10.1001/jamanetworkopen.2023.28886.
Tappia PS, Shah AK, Dhalla. N/S. The efficacy of vitamins in the prevention and treatment of cardiovascular disease. Int J Mol Sci. 2024;25:9761. doi: 10.3390/ijms25189761.
Naik M, Kamath US, Uppangala S, Adiga SK, Patil A. Vitamin D metabolites and analytical challenges. Anal Methods. 2023;15:399-410. doi: 10.1039/d2ay01692c.
Jones G. Pharmacokinetics of vitamin D toxicity. Am J Clin Nutr. 2008;88(2):582S-586S. doi: 10.1093/ajcn/88.2.582S.
Stokes CS, Lammert F. Vitamin D supplementation: less controversy, more guidance needed. F1000Res. 2016;5:F1000 Faculty Rev-2017. doi: 10.12688/f1000research.8863.1.
Jones KS, Meadows SR, Koulman A. Quantification and reporting of vitamin D concentrations measured in human milk by LC-MS/MS. Front Nutr. 2023;10:1229445. doi: 10.3389/fnut.2023.1229445.
Carter GD. 25 Hydorxyvitamin D assays: the quest for accuracy. Clin Chem. 2009;55(7):1300-2. doi: 10.1373/clinchem.2009.125906.
Hollis BW. Editorial: the determination of circulating 25-hydroxyvitamin D: no easy task. Clin Endocrinol Metab. 2004;89(7):3149-51. doi: 10.1210/jc.2004-0682.
Briggs LE, Whitewood JK, Williams EL. Analytical variation concerning total 25-hydroxyvitamin D measurement, where are we now? A DEQAS review of current assay performance. J Steroid Biochem Mol Biol. 2023;231:106328. doi: 10.1016/j.jsbmb.2023.106328.
Xu Z, Yu K, Zhang M, Ju Y, He J, Jiang Y, et al. Accurate clinical detection of vitamin D by mass spectrometry: A Review. Crit Rev Anal Chem. 2025;55(5):815-39. doi: 10.1080/10408347.2024.2316237.
Tripathi A, Ansari M, Dandekar P, Jain R. Analytical methods for 25-hydroxyvitamin D: advantages and limitations of the existing assays. J Nutr Biochem. 2022;109:109123. doi: 10.1016/j.jnutbio.2022.109123.
Cavalier E, Makris K, Heijboer AC, Herrmann M, JC. Vitamin D: Analytical advances, clinical impact, and ongoing debates on health perspectives. Clin Chem 2024;70(9):1104-1121. doi: 10.1093/clinchem/hvae056.
Çağlayan M, Gonel A, Tat TS, Celik O, Aykut FA, Okan AM, et al. False negative effect of high triglycerides concentration on vitamin D levels: A big data study. J Med Biochem. 2023;42(2):296-303. doi: 10.5937/jomb0-40106.
Gholamzad A, Khakpour N, Kabipour T, Gholamzad M. Association between serum vitamin D levels and lipid profiles: a cross-sectional analysis. Sci Rep. 2023;13:21058. doi: 10.1038/s41598-023-47872-5.
Han YY, Hsu SH, Su TC. Association between vitamin D deficiency and high serum levels of small dense LDL in middle-aged adults. Biomedicines. 2021;9(5):464. doi: 10.3390/biomedicines9050464.
Hernández-Álvarez E, Pérez-Barrios C, Blanco-Navarro I, Pérez-Sacristán B, Donoso-Navarro E, Silvestre RA, Granado-Lorencio F. Association between 25-OH-vitamin D and C-reactive protein as a marker of inflammation and cardi-ovascular risk in clinical practice. Ann Clin Biochem. 2019;(4):502-7. doi: 10.1177/0004563219851539.
Lim S, Lee K, Woo HY, Park H, Kwon MJ. Evaluation of Cobas 8000 analyzer series module e801 analytical performance. Ann Clin Lab Sci. 2019;49(3):372-9. PMID: 31308038.
McEnroe R, Durham A, Goldford M, Kondratovich M, Labadi S, Magari R, et al. E. Evaluation of Precision of Quantitative Measurement Procedures; Approved Guideline—Third Edition. CLSI document EP05-A3. Wayne, PA: Clinical and Laboratory Standards Institute; 2014.
Tholen DW, Kroll M, Astles JR, Caffo AL, Happe TM, Krouwer J, et al. Evaluation of the linearity of quantitative measurement procedures: A statistical approach; Approved Guideline. CLSI document EP06-A. Wayne, PA: Clinical and Laboratory Standards Institute; 2003.
Horowitz GL, Altaie S, Boyd JC, Ceriotti F, Garg U, Horn P, et al. Defining, Establishing, and Verifying Reference Intervals in the Clinical Laboratory; Approved Guideline—Third Edition. CLSI document EP28-A3c. Wayne, PA: Clinical and Laboratory Standards Institute; 2008.
Foroutan A, Guo AC, Vazquez-Fresno R, Lipfert M, Zhang L, Zheng J, et al. Chemical composition of commercial cow's milk. J Agric Food Chem. 2019;67(17):4897-914. doi: 10.1021/acs.jafc.9b00204.
Briggs LE, Whitewood JK, Williams EL. Analytical variation concerning total 25-hydroxyvitamin D measurement, where are we now? A DEQAS review of current assay performance. J Steroid Biochem Mol Biol. 2023;231:106328. doi: 10.1016/j.jsbmb.2023.106328.
Schorr P, Stokes CS, Volmer DA. Streamlined vitamin D metabolite fingerprinting analysis using isotope-coded multiplexing MS with cost-effective one-pot double derivatization. ACS Omega 2024;9(51):50660-70. doi: 10.1021/acsomega.4c08675.
Zhang M, Li Y, Xu D, Wang W, Zhou H, Yang X. Electrochemiluminescent/colorimetric monitoring 25(OH)D3 based on HOFs-g-C3N4-CeO2 functional composite. Mikrochim Acta. 2025;192(5):323. doi: 10.1007/s00604-025-07172-3.
Pilařová V, Socas-Rodríguez B, Nováková L, Essén S, Holm C, Turner C, et al. Analysis of vitamin D and its metabolites in biological samples - Part I: Optimization and comparison of UHPSFC-MS/MS and UHPLC-MS/MS methods. J Chromatogr B Analyt Technol Biomed Life Sci. 2024;1237:124087. doi: 10.1016/j.jchromb.2024.124087.
Tijerina A, Garza A, López A, Cavazos N, Romo A, Heya MS, et al. An HPLC-UV method to assess human plasma 25(OH)D3. Nutrients. 2024;16(14):2304. doi: 10.3390/nu16142304.
Junger S, Hoene M, Shipkova M, Danzl G, Schöberl C, Peter A, et al. Automated LC-MS/MS: Ready for the clinical routine Laboratory? J Mass Spectrom Adv Clin Lab. 2023;30:1-9. doi: 10.1016/j.jmsacl.2023.07.001.
Alexandridou A, Schorr P, Volmer DA. Comparing derivatization reagents for quantitative LC-MS/MS analysis of a variety of vitamin D metabolites. Anal Bioanal Chem. 2023; 415(19):4689-701. doi: 10.1007/s00216-023-04753-0.
Pilařová V, Socas-Rodríguez B, Nováková L, Holm C, Sandahl M, Turner C. Analysis of vitamin D and its metabolites in biological samples - Part II: Optimization of a sample preparation method for liver tissue. J Chromatogr B Analyt Technol Biomed Life Sci. 2024;1237:124088. doi: 10.1016/j.jchromb.2024.124088.
Wang X, Qin Q, Li F, Fu Y, Liu N. A novel LC-MS/MS method combined with derivatization for simultaneous quantifi-cation of vitamin D metabolites in human serum with diabetes as well as hyperlipidemia. RSC Adv. 2023;13(48):34157-66. doi: 10.1039/d3ra05700c.
Usoltseva L, Ioutsi V, Panov Y, Antsupova M, Rozhinskaya L, Melnichenko G, et al. Serum vitamin D metabolites by HPLC-MS/MS combined with differential ion mobility spectrometry: Aspects of sample preparation without derivatization. Int J Mol Sci. 2023;24(9):8111. doi: 10.3390/ijms24098111.
Gqamana PP, Militello L, McMaster JM, Daley SJ, Zhang YV. Analytical concordance of total vitamin D on a fully automated random-access LC-MS/MS platform. J Appl Lab Med. 2023;8(5):940-51. doi: 10.1093/jalm/jfad036.
Zhou Y, Du J, Liu Y, Xia J. Novel quality control strategies for the determination of 25-hydroxyvitamin D by LC-MS/MS. J Pharm Biomed Anal. 2024;239:115908. doi: 10.1016/j.jpba.2023.115908.
Kushioka T, Mano H, Matsuoka S, Nishikawa M, Yasuda K, Ikushiro S, Sakaki T. Analysis of vitamin D metabolites in biological samples using a nanoluc-based vitamin D receptor ligand sensing system: NLucVDR. J Steroid Biochem Mol Biol. 2023;233:106367. doi: 10.1016/j.jsbmb.2023.106367.
Squillacioti G, El Sherbiny S, Lettico V, Ghelli F, Panizzolo M, Scaioli G, et al. The quantification of vitamin D in humans: A promising, non-invasive and cost-effective method to measure 25-hydroxyvitamin D. Biomolecules. 2025;15(4):560. doi: 10.3390/biom15040560.
Wise SA, Camara JE, Sempos CT, Lukas P, Le Goff C, Peeters S, et al. Vitamin D Standardization Program (VDSP) intralaboratory study for the assessment of 25-hydroxyvitamin D assay variability and bias. J Steroid Biochem Mol Biol. 2021;212:105917. doi: 10.1016/j.jsbmb.2021.105917.
Parva NR, Tadepalli S, Singh P, Qian A, Joshi R, Kandala H, et al. Prevalence of vitamin D deficiency and associated risk factors in the US population (2011-2012). Cureus. 2018;10(6): e2741. doi: 10.7759/cureus.2741.
Manson JE, Brannon PM, Rosen CJ, Taylor CL. Vitamin D deficiency - is there really a pandemic? N Engl J Med. 2016;375(19):1817-20. doi: 10.1056/NEJMp1608005.
Sonderman JS, Munro HM, Blot WJ, Signorello LB. Reproducibility of serum 25-hydroxyvitamin d and vitamin D-binding protein levels over time in a prospective cohort study of black and white adults. Am J Epidemiol. 2012 Oct 1;176(7):615-21. doi: 10.1093/aje/kws141.
Institute of Medicine, Food and Nutrition Board. Dietary Reference intakes for calcium and vitamin D. Washington, DC: National Academy Press, 2010.
Wielders JP, Wijnberg FA. Preanalytical stability of 25(OH)-vitamin D3 in human blood or serum at room temperature: solid as a rock. Clin Chem. 200955(8):1584-5. doi: 10.1373/clinchem.2008.117366.
Colak A, Toprak B, Dogan N, Ustuner F. Effect of sample type, centrifugation and storage conditions on vitamin D con-centration. Biochemia Medica. 2013;23(3):321-5. doi: 10.11613/bm.2013.039.
Weiler HA, Sarafin K, Martineau C, Daoust JL, Esslinger K, Greene-Finestone LS, et al. Vitamin D status of people 3 to 79 years of age from the Canadian Health Measures Survey 2012-2019. J Nutr. 2023;153(4):1150-61. doi: 10.1016/j.tjnut.2023.02.026.
Lee JH, Seo JD, Lee K, Roh EY, Yun YM, Lee YW, et al. Multicenter comparison of analytical interfer-ences of 25-OH vitamin D immunoassay and mass spectrometry methods by endogenous interferents and cross-reactivity with 3-epi-25-OH-vitamin D3. Pract Lab Med. 2023;38:e00347. doi: 10.1016/j.plabm.2023.e00347.
Tai SS, Bedner M, Phinney KW. Development of a candidate reference measurement procedure for the determination of 25-hydroxyvitamin D3 and 25-hydroxyvitamin D2 in human serum using isotope-dilution liquid chromatography-tandem mass spectrometry. Anal Chem. 2010;82(5):1942-8. doi: 10.1021/ac9026862.
Stepman A, Vanderroost K, Uytfanghek T. Candidate reference measurements for serum 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3 by using isotope-dilution liquid-chromatography mass spectrometry. Clin Chem. 2011;57(3):441-8. doi: 10.1373/clinchem.2010.152553.
van den Ouweland JM, Beijers AM, van Daal H. Fast separation of 25-hydroxyvitamin D3 from 3-epi-25-hydroxyvitamin D3 in human serum by liquid chromatography-tandem mass spectrometry: Variable prevalence of 3-epi-25-hydroxyvitamin D3 in infants, children, and adults. Clin Chem. 2011;57(11):1618-9. doi: 10.1373/clinchem.2011.170282.
Lensmeyer G, Poquette M, Wiebe D, Binkley N. The C-3 epimer of 25-hydroxyvitamin D(3) is present in adult serum. J Clin Endocrinol Metab. 2012;97(1):163-8. doi: 10.1210/jc.2011-0584.
Ricci V, Esteban MP, Sand G, Menises MM. Interference of anti-streptavidin antibodies: More common than we thought? In relation to six confirmed cases. Clin Biochem. 2021;90:62-5. doi: 10.1016/j.clinbiochem.2021.01.013.
Diamandis EP, Christopoulos TK. The biotin-(strept)avidin system: principles and applications in biotechnology. Clin Chem. 1991;37(5):625-36. PMID: 2032315.
Piketty ML, Polak M, Flechtner I, Gonzales-Briceño L, Souberbielle JC. False biochemical diagnosis of hyperthyroidism in streptavidin-biotin-based immunoassays: the problem of biotin intake and related interferences. Clin Chem Lab Med. 2017;55(6):780-8. doi: 10.1515/cclm-2016-0606.
Li J, Wagar EA, Meng QH. Comprehensive assessment of biotin interference in immunoassays. Clin Chim Acta. 2018;487:293-8. doi: 10.1016/j.cca.2018.10.013.
Zhou Y, Du J, Liu Y, Xia J. Novel quality control strategies for the determination of 25-hydroxyvitamin D by LC-MS/MS. J Pharm Biomed Anal. 2024;239:115908. doi: 10.1016/j.jpba.2023.115908.
Wise SA, Kuszak AJ, Camara JE. Evolution and impact of Standard Reference Materials (SRMs) for determining vitamin D metabolites. Anal Bioanal Chem. 2024;416(9):2335-58. doi: 10.1007/s00216-024-05143-w.
Chen N, Wan Z, Han SF, Li BY, Zhang ZL, Qin LQ. Effect of vitamin D supplementation on the level of circulating high-sensitivity C-reactive protein: a meta-analysis of randomized controlled trials. Nutrients. 2014;6(6):2206-16. doi: 10.3390/nu6062206.
Lin J, Liu J, Davies ML, Chen W. Serum vitamin D level and rheumatoid arthritis disease activity: Review and me-ta-analysis. PLoS One. 2016;11(1):e0146351. doi: 10.1371/journal.pone.0146351.
Moslemi E, Musazadeh V, Kavyani Z, Naghsh N, Shoura SMS, Dehghan P. Efficacy of vitamin D supplementation as an adjunct therapy for improving inflammatory and oxidative stress biomarkers: An umbrella meta-analysis. Pharmacol Res. 2022; 186:106484. doi: 10.1016/j.phrs.2022.106484.
Mousa A, Naderpoor N, Teede H, Scragg R, de Courten B. Vitamin D supplementation for improvement of chronic low-grade inflammation in patients with type 2 diabetes: a systematic review and meta-analysis of randomized controlled trials. Nutr Rev. 2018;76(5):380-94. doi: 10.1093/nutrit/nux077.
Mansournia MA, Ostadmohammadi V, Doosti-Irani A, Ghayour-Mobarhan M, Ferns G, Akbari H, et al. The effects of vitamin D supplementation on biomarkers of inflammation and oxidative stress in diabetic patients: A systematic review and meta-analysis of randomized controlled trials. Horm Metab Res. 2018;50(6):429-40. doi: 10.1055/a-0630-1303.
Cannell JJ, Grant WB, Holick MF. Vitamin D and inflammation. Dermatoendocrinol. 2015;6(1):e983401. doi: 10.4161/19381980.2014.983401.
Sergeev IN. 1,25-Dihydroxyvitamin D3 and type 2 diabetes: Ca2+-dependent molecular mechanisms and the role of vitamin D status. Horm Mol Biol Clin Investig. 2016;26(1):61-5. doi: 10.1515/hmbci-2015-0069.
American Diabetes Association. Diagnosis and classification of diabetes mellitus. Diabetes Care. 2012;35:S64-S71. doi: 10.2337/dc12-s064.
Miyamoto H, Kawakami D, Hanafusa N, Nakanishi T, Miyasaka M, Furutani Y, et al. Determination of a serum 25-hydroxyvitamin D reference ranges in Japanese adults using fully automated liquid chromatography-tandem mass spectrometry. J Nutr. 2023;153(4):1253-64. doi: 10.1016/j.tjnut.2023.01.036.
Wallace AM, Gibson S, de la Hunty A, Lamberg-Allardt C, Ashwell M. Measurement of 25-hydroxyvitamin D in the clinical laboratory: Current procedures, performance characteristics and limitations. Steroids. 2010;75(7):477-88. doi: 10.1016/j.steroids.2010.02.012.
Sempos CT, Lindhout E, Heureux N, Hars M, Parkington DA, Dennison E, et al. Towards harmonization of directly measured free 25-hydroxyvitamin D using an enzyme-linked immunosorbent assay. Anal Bioanal Chem. 2022;414(27):7793-803. doi: 10.1007/s00216-022-04313-y.
Alexandridou A, Stokes CS, Volmer DA. Measurement of serum free vitamin D concentrations: Importance, challenges, and the emerging role of mass spectrometry. Clin Chem. 2025;71(2):254-65. doi: 10.1093/clinchem/hvae202.
Ross AC, Manson JE, Abrams SA, Aloia JF, Brannon PM, Clinton SK, et al. The 2011 report on dietary reference intakes for calcium and vitamin D from the Institute of Medicine: what clinicians need to know. J Clin Endocrinol Metab. 2011;96(1):53-8. doi: 10.1210/jc.2010-2704.
Lapauw B, Laurent MR, Rozenberg S, Body JJ, Bruyère O, Gielen E, Goemaere S, Iconaru L, Cavalier E. When and how to evaluate vitamin D status? A viewpoint from the Belgian Bone Club. Nutrients 2024;16(15):2388. doi: 10.3390/nu16152388.
Plebani M, Zaninotto M, Giannini S, Sella S, Fusaro M, Tripepi G, Gallieni M, Herrmann M, Cozzolino M. Vitamin D assay and supplementation: still debatable issues. Diagnosis. 2024;12(1):35-44. doi: 10.1515/dx-2024-0147.
Marques Vidigal V, Aguiar Junior PN, Donizetti Silva T, de Oliveira J, Marques Pimenta CA, Vitor Felipe A, Manoukian Forones N. Genetic polymorphisms of vitamin D metabolism genes and serum level of vitamin D in colorectal cancer. Int J Biol Markers. 2017;32(4):e441-e446. doi: 10.5301/ijbm.5000282.
Ghiasvand R, Rashidian A, Abaj F, Rafiee M. Genetic variations of vitamin D receptor and vitamin D supplementation interaction in relation to serum vitamin D and metabolic traits: a systematic review and meta-analysis. Int J Vitam Nutr Res. 2023;93(6):535-58. doi: 10.1024/0300-9831/a000762.
Herrmann M. Assessing vitamin D metabolism - four decades of experience. Clin Chem Lab Med. 2023;61(5):880-94. doi: 10.1515/cclm-2022-1267.
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