Copper deficiency in sheep : An assessment of relationship between concentrations of copper in serum and plasma

Authors: Smith SL, Laven RA
Publication: New Zealand Veterinary Journal, Volume 56, Issue 6, pp 334-338, Dec 2008
Publisher: Taylor and Francis

Animal type: Livestock, Production animal, Ruminant, Sheep
Subject Terms: Circulatory system/haematology, Clinical pathology, Copper, Trace elements, Diagnostic procedures, Poisoning - chemical
Article class: Short Communication

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Abstract: AIM: To assess the relationship between concentrations of copper in serum and plasma in sheep.
METHODS: Concentrations of Cu were measured in paired serum and heparinised plasma samples collected from 110 sheep in nine flocks. Linear regression was used to evaluate whether flock or gender had a significant effect on the association between concentrations of Cu in serum and plasma. The individual results for concentrations of Cu in serum were then compared with those from plasma, using correlation and limits of agreement plotting.
RESULTS: Concentrations of Cu in serum ranged from 7.3 to 22 (mean 14.0) μmol/L, while concentrations in plasma ranged from 9 to 27 (mean 16.3) μmol/L. On average, concentrations of Cu in serum were 2.3 μmol/L lower than in plasma. Over the range of values seen in this study, concentrations of Cu in plasma and serum were significantly correlated (r=0.89), and mean concentrations in serum were 87% of those in plasma. There was no effect of flock or gender on the relationship between concentrations of Cu in serum and plasma. Despite the significant correlation, there was marked variability between individual samples in the proportion of Cu that was lost during clotting, with the 95% limits of agreement for serum Cu ranging from 70 to 104% of the plasma concentration.
CONCLUSIONS: As in cattle, the individual variability in the loss of Cu during clotting in sheep is too great for concentration of Cu in serum to be used as a substitute for that in plasma.
CLINICAL RELEVANCE: When assessing the blood Cu pool as part of the diagnosis of Cu-responsive disease in sheep, the concentration of Cu in plasma should be measured in preference to that of serum. We suggest that a range of 4.5 to 9 μmol/L in plasma be used to define marginal Cu status in sheep.
KEY WORDS: Copper, sheep, plasma, serum, diagnosis

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