Venous blood is widely used in clinical diagnosis and evaluation; however, venous puncture is difficult to perform, especially in some small experimental animals, such as rabbits and mice. The veins are small and friable, the blood collection procedure does not always go smoothly, and forced extrusion of the vein causes hemolysis to occur. Therefore, venous blood is difficult to collect for laboratory analysis, whereas arterial blood is more convenient to obtain in small animals. It is well known that venous blood and arterial blood are different in regard to oxygen and carbon dioxide levels; therefore, blood gas analysis was performed only on arterial blood . Other studies also showed that the results from a complete blood count obtained from canine and postpubertal rabbit venous and arterial blood samples may not be comparable [9, 10]. However, studies on whether arterial blood can be used instead of venous blood for hepatic function, renal function and serum lipid levels in rabbits are rare.
In our study, we used healthy rabbits as a model, analyzing the differences in some common biochemical assay parameters between arterial blood and venous blood. We found that all of the parameters showed excellent consistency by Bland-Altman analysis, and the two samples correlated well. The results of Deming regression analysis indicated that most of the parameters demonstrated excellent consistency between arterial blood and venous blood. However, it can be considered that the proportional deviation was existed in Ur, Cr, TG and LDL between venous blood and arterial blood via the analysis of 95% confidence intervals of slopes. Whereas constant deviation was found in Ur, Cr and HDL between venous blood and arterial blood via the analysis of intercepts. Moreover, we noticed that there are significant differences between venous blood and arterial blood in ALP, TP, Cr and some blood lipid parameters, including TC, TG, HDL, LDL, which may be partly caused by hemolysis of the venous blood, which is unavoidable when collecting venous blood from rabbits. Although samples with gross hemolysis were excluded from our study, there is also a discharge of the cell constituents into serum or plasma due to hemolysis undetectable by visual inspection . Previous clinical research has shown that hemolysis affects the plasma concentration of a whole range of biochemical parameters, whereas the most prominent effect of hemolysis is observed for AST, lactate dehydrogenase, potassium and total bilirubin. The differences in ALP, HDL, TP and some other analytes were statistically significant but remained within Clinical Laboratory Improvement Amendments (CLIA) limits . Giuseppe Lippi reported that hemolysis generated a consistent trend towards overestimation of ALT, AST, Cr and Ur . A study showed that hemolysis interference was detected for ALP, AST, GGT, TP, ALT and other analytes that were not mentioned in our study . From the above studies, we found that different studies obtained different parameters that were affected by hemolysis. In our study, ALP and TP were higher in venous blood, while AST and ALT showed no difference, which may be caused by hemolysis; for experiments performed on different species, the results may be partly different. For a higher Cr in arterial blood, we think that this is a normal phenomenon caused by filtering by the kidneys and that part of the metabolic substance was excreted with urine. Ur in arterial blood should be higher than that in venous blood, but our study showed that there are no differences between the two samples; furthermore, there may be an overestimation of venous blood Ur due to venous blood hemolysis. A previous study showed that Ur is elevated with moderate hemolysis, even at the greatest degree of hemolysis, and no interference was detected for Cr . This is coincident with our study. However, the biases of ALP, TP, Cr and blood lipids were subtle and not deemed clinically important; therefore, we considered arterial blood instead of venous blood for routine biochemical parameters in rabbits.
A previous study has shown that arterial and venous blood can be used interchangeably to study the effect of blood concentrations of common soluble surrogate markers of atherosclerosis in humans, and there are virtually the same LDL, HDL, TC and TG levels in arterial plasma compared to venous plasma [15, 16]. In our study, we found that in rabbits, all the lipid parameters of the venous sample were higher than those of the arterial sample, which may be caused by venous blood hemolysis that is undetectable by visual inspection, as explained above. Whereas the mean differences are subtle, the biases between lipid parameters of the two samples are subtle, and the agreements of lipid parameters between the two samples are good. The correlations between lipid parameters of the two samples by Deming regression were good; therefore, we think that in rabbits, arterial blood can be used for rough estimation of the lipid level while taking the magnitude of bias into account.
Our study was limited by the relatively small sample size and simple laboratory parameters. A larger sample size and more study parameters are needed for a more accurate and comprehensive result. Moreover, in our study, we excluded only gross hemolysis and did not evaluate the degree of hemolysis; therefore, the reasons for the higher venous value of ALP, TP and blood lipid parameters were based entirely on supposition. Studies on the influence of hemolysis on rabbit venous blood may provide an exact result.
Importantly, venous blood collection cannot avoid hemolysis, so we focused on using arterial blood instead of venous blood, even though the samples have invisible hemolysis, which may provide more accurate biochemical parameters.