Concentration of dipotassium ethylenediaminetetraacetic acid but not lithium heparin affects total protein determination in equine synovial fluid

17 Oct 2020

Jimenez Rihuete, P., Villarino, N., Pelisiak, A., Rubio-Martinez, L. M.

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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.


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.


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.


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.


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.