Use of selected biochemical indices in blood/peritoneal effusion in diagnostics of gastrointestinal tract damage in dogs

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Peritoneal effusion is a pathological accumulation of fluid inside the abdominal cavity.When deciding on the therapeutic approach, it is essential to determine in a majority of patients the main cause of peritoneal effusion formation.Due to its clinical impact, the aim of our study was to evaluate the importance of blood and effusion biochemical analysis as a minimally invasive diagnostic technique in patients with peritoneal effusion.A study by Oz et al. (2016) described increased potassium concentration in peritoneal effusion in a dog with gastrointestinal tract (GIT) perforation.In our study, besides the potassium concentration, we extended the indices analysed to include total protein, glucose, lactate and creatinine.The aim of our study was to evaluate the role of the selected variables for the diagnostics of GIT damage in dogs.

Materials and Methods
Subjects enrolled in the study were patients with peritoneal effusion of different aetiologies, that were presented to the Small Animal Clinic, Faculty of Veterinary Medicine, University of Veterinary Sciences Brno.As part of the standard diagnostic procedure, samples of peripheral blood and peritoneal fluid were obtained from these patients and analysed.Blood samples were obtained by venepuncture of v. cephalica antebrachii, v. saphena lateralis or v. jugularis.Peritoneal fluid samples were obtained by ultrasound-guided abdominocentesis.Samples were analysed in the Small Animal Clinical Laboratory at the University of Veterinary Sciences Brno (SACL) either immediately after obtaining or they were centrifuged (2,945 × g for 10 minutes) and stored at 4 °C for a maximum of 48 h before being analysed in SACL.The biochemical properties analysed from the blood and peritoneal fluid samples included potassium, total protein, glucose, lactate and creatinine.These indices were analysed on the Abbott Architect c4000 analyser (Abbott Laboratories, Lake Bluff, IL, USA).The reagent sets used were Total Protein, Creatinine, Glucose, Lactate Dehydrogenase, ICT module (Abbott Laboratories, Lake Bluff, IL, USA) and Lac (Randox Laboratories Ltd, Crumlin, County Antrim, UK).Potassium concentrations were measured potentiometrically, other selected indices were measured photometrically.
According to the GIT condition, patients were divided into two groups -patients with GIT damage and patients without GIT damage.Effusion-to-blood concentration ratios of selected indices were obtained and this ratio was then compared between the two study groups.Data were statistically analysed using the Real Statistics Resource Pack software (Release 6.3) in Microsoft Excel (version 16.26;Microsoft Corporation,Redmond,WA). Shapiro-Wilk test was used for evaluation of normal data distribution.Differences between the two study groups (patients with GIT damage versus patients without GIT damage) were statistically analysed with two-sample t-test.The level of significance was set at 5% (P ≤ 0.05).

Results
Twenty-nine dogs with peritoneal effusion were enrolled in the study.There were more females (57%) in the study than males.The patients' mean age was 7 ± 3.8 years (range of 6 months to 12 years).The 29 patients were of 23 different breeds.The most often represented breeds were the Yorkshire terrier and Pug; two dogs were crossbreeds.
There were 11 dogs in the group of patients with GIT damage and 18 dogs in the group of patients without GIT damage.Dogs in the study group of patients with GIT damage were diagnosed e.g. with GIT neoplasia, gastric dilation and volvulus (GDV), GIT foreign body, small intestine invagination, colon perforation or enterotomy wound dehiscence.Dogs in the study group of patients without GIT damage were diagnosed e.g. with a portosystemic shunt, peritonitis, pyometra, neoplastic disease outside the GIT, heart failure or diaphragmatic hernia.
Concentrations measured in blood/fluid of patients with and without GIT damage are shown in Tables 1-5.Comparison between the two groups is illustrated in Figs 1-5.No significant difference in potassium, total protein, glucose, lactate and creatinine concentration was found between the two groups.

Discussion
Obtaining peritoneal fluid samples and their analysis are technically undemanding procedures that are frequently used as a standard approach to diagnosis of various diseases.However, the use of peritoneal fluid biochemical analysis for diagnosing GIT damage is controversial.Based on a published case report by Oz et al. (2016), we decided to evaluate whether GIT damage is associated with increased potassium in peritoneal fluid in dogs.In the cited report, authors described a clinical case of a dog with increased concentrations of potassium in peritoneal fluid in association with gastric perforation (Oz et al. 2016).Pathophysiology of this finding can be explained by the fact that potassium is highly concentrated in the gastric content.In available literature, increased potassium concentration is associated mainly with uroperitoneum (Schmiedt et al. 2001;Tsompanidou et al. 2015), because potassium is secreted from the body mainly by the kidneys (Thier 1986).Our study results did not prove a significant increase of potassium in peritoneal fluid of patients with GIT damage.Unfortunately, published studies examining gastric perforation do not document potassium concentration in peritoneal fluid (Reed 2002;Enberg et al. 2006;Dayer et al. 2013).
Analysis of total protein, lactate, glucose and creatinine concentrations in peritoneal fluid or blood is easily available.Total protein is a basic indicator to analyse in peritoneal fluid and based on its concentration, we can categorize effusions as transudate, modified transudate and exudate (Rakich and Latimer 2011), or as a protein-poor transudate, protein-rich transudate and exudate (Stockham and Scott 2008).In our study, we did not distinguish between the above-mentioned types of effusions, however, the total protein concentrations did not differ very much between the study groups of patients, therefore, it cannot be considered as a suitable indicator for GIT damage diagnostics.
Lactate and glucose concentrations are indices that are most often associated with septic conditions.Bacterial peritonitis can arise from GIT perforation because of high levels of potentially pathogenic bacteria localized in GIT, however, no other association between these indices and GIT damage has been described yet.Our study did not show a significant relationship between glucose or lactate concentrations in peritoneal fluid and GIT damage, either.However, adequate analysis immediately after sampling and according to selected methodology is important for the assessment of these indices; otherwise, the glucose Creatinine concentration is one of the main indicators used for diagnosing kidney disease and urinary tract disease in general.Its increased levels are diagnostic in uroperitoneum (Alleman 2003;Dempsey and Ewing 2011;Tsompanidou et al. 2015;Athanasiou et al. 2019), however, there are no available sources describing its increased levels in patients with GIT damage.Although the mean creatinine concentration in our study population was higher in the group of patients without GIT damage, the difference between the two groups was not significant.
In conclusion, no significant difference in potassium, total protein, glucose, lactate and creatinine concentrations was found between the two study groups.According to our results, analysis of these indices does not seem to be valuable for the diagnostics of GIT damage.However, our study results could have been affected by the small number of our study population, which is why we would like to continue our observations and evaluate a larger study population in the future.

Fig. 1 .
Fig. 1.A boxplot representing the mean value and standard deviation of effusion-to-blood potassium concentration in two selected groups of patients (patients with and without gastrointestinal tract damage).Left boxplot represents patients with gastrointestinal tract damage and right boxplot represents patients without gastrointestinal tract damage.C e :C b -effusion-to-blood potassium concentration

Fig. 5 .
Fig. 5.A boxplot representing mean value and standard deviation of effusion-to-blood creatinine concentration in two selected groups of patients (patients with and without gastrointestinal tract damage).Left boxplot represents patients with gastrointestinal tract damage and right boxplot represents patients without gastrointestinal tract damage.C e :C b -effusion-to-blood potassium concentration

Table 1 .
Potassium concentration (mmol/l) in blood/effusion of patients with and without gastrointestinal tract damage.
e :C b -effusion-to-blood potassium concentration

Table 2 .
Total protein concentration (g/l) in blood/effusion in patients with and without gastrointestinal tract damage.
e :C b -effusion-to-blood potassium concentration

Table 3 .
Glucose concentration (mmol/l) in blood/effusion in patients with and without gastrointestinal tract damage.

Table 4 .
Lactate concentration (mmol/l) in blood/effusion in patients with and without gastrointestinal tract damage.
e :C b -effusion-to-blood potassium concentration Table 5. Creatinine concentration (μmol/l) in blood/effusion in patients with and without gastrointestinal tract damage.Patients with GIT damage n = 11 Patients without GIT damage n = 18 GIT -gastrointestinal tract; C e :C b -effusion-to-blood potassium concentration