Table Info

Table 2.

Agreement in the identification of microcrystals (kappa index) compared with reference with and without DMSO for both observers (disagreement shown in bold and underlined)

Reference	DMSO+ observer 1			DMSO+ observer 2			DMSO− observer 1			Observer 2
Reference	Negative	MSU	CPP	Negative	MSU	CPP	Negative	MSU	CPP	Negative	MSU	CPP
Negative	12	0	0	2	1	1	11	0	1	0	0	0
MSU	0	8	0	0	8	0	1	7	0	5	1	0
CPP	0	0	10	0	0	9	4	0	6	2	1	2

Agreement kappa: 1.00 for reference vs. DMSO+ observer 1; kappa: 0.845 for reference vs. DMSO+ observer 2; kappa: 0.691 for reference vs. DMSO− observer 2; kappa: 0.111 for reference vs. DMSO− observer 2

Declarations

Author contributions

FPR, ELB, FL, NS, TU, and JJMM: Conceptualization, Writing—review & editing. FPR and ELB: Data curation, Writing—original draft. FPR, ELB, FL, NS, TU, and JJMM read and approved the submitted version.

Conflicts of interest

The authors declare that they have no conflicts of interest.

Ethical approval

The study was included within a prospective inception gout cohort study approved by Cruces University Hospital Ethics and Clinical Investigation Committee (CEIC Cruces).

Consent to participate

Written informed consent was obtained and signed by patients and investigators to use exceeds of biological samples, and approved by the CEIC Cruces.

Consent to publication

Not applicable.

Availability of data and materials

Data can be obtained by contacting Fernando Pérez-Ruiz (fernando.perezruiz@osakidetza.eus).

Funding

FPR was funded by a grant from Asociación de Reumatólogos de Cruces [04/2022]. The funders had no role in study design, data collection, and analysis, decision to publish, or preparation of the manuscript.

Copyright

References

Pascual E, Sivera F, Andrés M. Synovial fluid analysis for crystals. Curr Opin Rheumatol. 2011;23:161–9. [DOI] [PubMed]

Richette P, Doherty M, Pascual E, Barskova V, Becce F, Castaneda J, et al. 2018 updated European league against rheumatism evidence-based recommendations for the diagnosis of gout. Ann Rheum Dis. 2020;79:31–8. [DOI] [PubMed]

Zhang W, Doherty M, Bardin T, Barskova V, Guerne PA, Jansen TL, et al. European league against rheumatism recommendations for calcium pyrophosphate deposition. Part I: terminology and diagnosis. Ann Rheum Dis. 2011;70:563–70. [DOI] [PubMed]

Kienhorst LB, Janssens HJ, Eijgelaar RS, Radstake TR, van Riel PL, Janssen M. The detection of monosodium urate crystals in synovial fluid after long-term and varying storage conditions. Joint Bone Spine. 2015;82:470–1. [DOI] [PubMed]

Pastor S, Bernal JA, Caño R, Gómez-Sabater S, Borras F, Andrés M. Persistence of crystals in stored synovial fluid samples. J Rheumatol. 2020;47:1416–23. [DOI] [PubMed]

Perez-Ruiz F, Castillo E, Chinchilla SP, Herrero-Beites AM. Clinical manifestations and diagnosis of gout. Rheum Dis Clin North Am. 2014;40:193–206. [DOI] [PubMed]

Hornberger K, Yu G, McKenna D, Hubel A. Cryopreservation of hematopoietic stem cells: emerging assays, cryoprotectant agents, and technology to improve outcomes. Transfus Med Hemother. 2019;46:188–96. [DOI] [PubMed] [PMC]

Lovelock JE, Bishop MW. Prevention of freezing damage to living cells by dimethyl sulphoxide. Nature. 1959;183:1394–5. [DOI] [PubMed]

Li R, Johnson R, Yu G, McKenna DH, Hubel A. Preservation of cell-based immunotherapies for clinical trials. Cytotherapy. 2019;21:943–57. [DOI] [PubMed] [PMC]

10.

Kim MY, Yoon HY, Lee S. The advantage of the supercooling storage method for transplantable sources: human umbilical vessel endothelial cells and mouse skin grafts. Transplant Proc. 2021;53:1756–61. [DOI] [PubMed]

11.

Tausche AK, Gehrisch S, Panzner I, Winzer M, Range U, Bornstein SR, et al. A 3-day delay in synovial fluid crystal identification did not hinder the reliable detection of monosodium urate and calcium pyrophosphate crystals. J Clin Rheumatol. 2013;19:241–5. [DOI] [PubMed]

12.

McGill NW, Swan A, Dieppe PA. Survival of calcium pyrophosphate crystals in stored synovial fluids. Ann Rheum Dis. 1991;50:939–41. [DOI] [PubMed] [PMC]

13.

Perez-Ruiz F, Modesto-Caballero MC. Crystal-associated arthritis: gout. In: Mandell BF, editor. Synovial fluid analysis and the evaluation of patients with arthritis. Springer, Cham; 2022. pp. 91–100. [DOI]

14.

Pavic K, McGill V, D’Souza M, McGill N. The preservation of synovial fluid using dimethyl sulfoxide. Ann Clin Biochem. 2022;59:296–301. [DOI] [PubMed]

15.

Lumbreras B, Pascual E, Frasquet J, González-Salinas J, Rodríguez E, Hernández-Aguado I. Analysis for crystals in synovial fluid: training of the analysts results in high consistency. Ann Rheum Dis. 2005;64:612–5. [DOI] [PubMed] [PMC]