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Concentration of dipotassium ethylenediaminetetraacetic acid but not lithium heparin affects total protein determination in equine synovial fluid
  1. Pablo Jimenez Rihuete1,
  2. Nicolas Villarino2,
  3. Alicja Pelisiak3 and
  4. Luis M Rubio-Martinez1,4
  1. 1 Department Equine Clinical Science, University of Liverpool Institute of Veterinary Science, Liverpool, Merseyside, UK
  2. 2 Program in Individualized Medicine, Washington State University, Pullman, Washington, USA
  3. 3 Wildlife Center, RSPCA Stapeley Grange, Nantwich, UK
  4. 4 Sussex Equine Hospital, Ashington, West Sussex, UK
  1. Correspondence to Dr Luis M Rubio-Martinez, Susssex Equine Hospital, Ashington RH20 3BB, West Sussex, UK; luis.rubiomartinez{at}


Background Refractometric determination of total protein (TP) in synovial fluid (SF) is commonly used for diagnosis and monitoring of synovial sepsis in horses. Previous studies have shown that elevated concentrations of certain anticoagulants may overestimate refractometric determination of TP concentration.

Objectives The aim of the study was to evaluate the effect of different concentrations of dipotassium EDTA (K2EDTA) and lithium heparin (LH) on TP determination by using a hand-held refractometer in equine synovial fluid.

Study design Cross-section observational study.

Methods Thirty samples of synovial fluid obtained from 22 horses with different synovial conditions were collected. Synovial fluid samples were separated into different aliquots and placed in commercially available collection tubes containing K2EDTA or LH at four different concentrations (1.76, 3.52, 7.04 and 17.6 mg/ml for K2EDTA; 16, 32, 64 and 160 IU/ml for LH) . Refractometric TP determination was performed on untreated and K2EDTA and LH aliquots with a hand-held refractometer and by spectophotometric Biuret method as the gold standard.

Results Refractometric TP determination was overestimated in SF samples containing 10 times the recommended K2EDTA concentrations. Lower concentrations of K2EDTA and LH concentrations did not affect refractometric TP determinations.

Main limitations Limited number of samples mostly obtained from large synovial structures.

Conclusion To avoid incorrect TP determination, the use of LH containing collection tubes may be an appropriate alternative when the SF volume available is not enough to fill the K2EDTA collection tube.

  • orthopaedics
  • lameness
  • joint diseases
  • joint sepsis
  • synovial fluid
  • total protein
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  • Funding Study funded by the University of Liverpool, Institute of Veterinary Science.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data availability statement All data relevant to the study are included in the article or uploaded as supplementary information. Data are available on reasonable request.

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