Abstract
The objective of this study was to investigate possible associations between serum triglyceride and canine pancreatic lipase immunoreactivity (cPLI) concentrations in miniature schnauzers. One hundred and ninety-five miniature schnauzers were enrolled and divided into two groups based on whether they had normal (group 1) or increased (group 2) serum triglyceride concentrations. Serum cPLI concentrations were measured and compared between groups. A significant positive correlation was seen between serum triglyceride and cPLI concentrations (Spearman r=0.321; P<0.0001). Miniature schnauzers with hypertriglyceridemia had a significantly higher median serum cPLI concentration (99.5 μg/L) than miniature schnauzers with normal serum triglyceride concentrations (median cPLI concentration 39.3 μg/L; P=0.0001). A cutoff value of 862 mg/dL was selected for serum triglyceride concentrations based on receiver operator characteristic analysis. Miniature schnauzers with severe hypertriglyceridemia (≥862 mg/dL) were 4.5 times more likely to have a serum cPLI concentration consistent with pancreatitis (≥200 μg/L) than miniature schnauzers with a normal serum triglyceride concentration. The present study supports an association between hypertriglyceridemia (especially when severe [≥862 mg/dL]) and high cPLI concentrations in miniature schnauzers.
Introduction
Primary (idiopathic) hypertriglyceridemia is a common condition in miniature schnauzers in the United States.1 In a recent study, hypertriglyceridemia was present in 32.8% of 192 miniature schnauzers investigated. Also, hypertriglyceridemia was shown to be age related, with a much higher prevalence in older miniature schnauzers.1 Hypertriglyceridemia in miniature schnauzers has previously been shown to be associated with an abnormal accumulation of very low-density lipoproteins (VLDL) or a combination of VLDL and chylomicrons, with or without hypercholesterolemia.2,3 The fact that hypertriglyceridemia is especially prevalent within a certain breed suggests a hereditary mechanism, but the metabolic and genetic bases of this disorder have not been identified.2,4
Investigations into the disease conditions potentially associated with hypertriglyceridemia have only recently been reported in dogs. For example, similar to humans, hypertriglyceridemia recently has been reported to be associated with hepatobiliary disease in miniature schnauzers and dogs of other breeds.5,6 In humans, severe hypertriglyceridemia is also a known risk factor for pancreatitis.7–9 Miniature schnauzers are generally considered to have a high incidence of pancreatitis.10–13 In a recent study, bivariable screening showed that miniature schnauzers were 4.1 times (95% confidence interval [CI] 1.9 to 9.2; P<0.001) more likely to have pancreatitis than were dogs of other breeds.12 The basis for this predisposition is unknown, but hypertriglyceridemia has long been considered a possible cause of pancreatitis in the miniature schnauzer.2,3,10 Studies investigating any etiological association between these two disorders in dogs are lacking, and this hypothesis is mainly based on clinical impressions.
In vitro studies support the concept that hypertriglyceridemia can initiate pancreatic inflammation, and evidence supports that high-fat diets or even a single fatty meal can induce pancreatitis in dogs.10,14,15 In contrast to hypertriglyceridemia, hypercholesterolemia does not appear to be a risk factor for pancreatitis in either humans or dogs.7,8,16 Recognition of an association between hypertriglyceridemia and pancreatitis in miniature schnauzers is clinically important, because management of hypertriglyceridemia with low-fat diets and/or lipid-lowering drugs may prevent or resolve pancreatitis in these dogs.
Until recently, a clinical diagnosis of pancreatitis was problematic in dogs, because no specific and sensitive tests were available. The analytical validation of a recently developed enzyme-linked immunosorbent assay (ELISA) specific for canine pancreatic lipase (i.e., canine pancreatic lipase immunoreactivity [cPLI]) has facilitated the diagnosis of pancreatitis in dogs, as it has been reported to be sensitive (reported sensitivity ranging from 64% for mild pancreatitis to 82% for severe pancreatitis) and specific for the diagnosis of canine pancreatitis.17–25 The aim of this study was to investigate possible associations between serum triglyceride and cPLI concentrations in a large group of miniature schnauzers.
Materials and Methods
Serum samples from 195 miniature schnauzers were collected, and triglyceride and cPLI concentrations were measured. The samples had been submitted to the Gastrointestinal Laboratory by veterinarians as part of their diagnostic evaluation between September 2004 and April 2005.
Serum samples were collected on a sequential basis, and no bias was given to lipemic samples. Based on the submission form, food was withheld from dogs for at least 12 hours before blood collection. Serum triglyceride concentrations were measured by an enzymatic in vitro assay (reference range 26 to 108 mg/dL).a Serum cPLI concentration was measured using an in-house ELISA as described elsewhere.17 The reported reference range for cPLI is 2.2 to 102.1 μg/L, and serum cPLI concentrations ≥200 μg/L are considered consistent with canine pancreatitis.17 Serum cPLI concentrations that fall between 102.1 and 200 μg/L are considered equivocal, and retesting (which depends on the clinical signs of each dog and the response to treatment) is suggested. Worth noting is that the cPLI test used in this study has been replaced. The cPLI is currently measured using Spec cPL,b which shows the same clinical performance as the original cPLI assay used in this study, but it has a different reference range (0 to 200 μg/L) than that of the assay used in the present study.
Dogs were divided into two groups according to their serum triglyceride concentration. Group 1 consisted of dogs with serum triglyceride concentrations within the reference range, while group 2 consisted of dogs with serum triglyceride concentrations above the upper limit of the reference range (>108 mg/dL). Serum cPLI concentrations were subsequently compared between the two groups.
Statistical Analysis
The data were analyzed for normal distribution using the Kolmogorov-Smirnov test. All data failed normality testing, and nonparametric methods were used for further analysis. The data were analyzed for correlation between serum cPLI and triglyceride concentrations using the Spearman’s rank correlation coefficient. The median serum cPLI concentrations were compared between groups with the Mann-Whitney U test. Receiver Operator Characteristic (ROC) analysis was performed, and the likelihood ratio (which provides an estimate of how much a positive or negative result affects the likelihood that an animal will have the disease) was calculated.26 Proportions of dogs with increased serum cPLI concentrations were compared between groups using Fisher’s exact tests. Odds ratios and their 95% CIs were also calculated. Dogs with serum cPLI concentrations in the equivocal range (i.e., neither within the reference range nor consistent with pancreatitis; n=33) were excluded from this analysis, as they could potentially affect the validity of the results. All statistical analyses were performed using a statistical software package,c and a P value of <0.05 was considered significant.
Results
Between September 2004 and April 2005, serum samples submitted to the Gastrointestinal Laboratory were collected from 195 consecutive miniature schnauzers. A significant but weak positive correlation was seen between serum cPLI and triglyceride concentrations (Spearman r=0.3215; P<0.0001; Figure 1⇓). The ROC analysis and calculation of likelihood ratios (at different triglyceride concentrations for serum cPLI concentrations that were consistent with pancreatitis) revealed that the likelihood ratio remained close to 1 for serum triglyceride concentrations <800 mg/dL and increased sharply for serum triglyceride concentrations >800 mg/dL [Figure 2⇓]. The lowest serum triglyceride concentration associated with a statistically significant increased likelihood for a cPLI ≥200 μg/L (a serum cPLI concentration that is considered consistent with pancreatitis) was 862 mg/dL. This concentration was associated with a likelihood ratio of 3.3 for a cPLI ≥200 μg/L and was used for further statistical analysis.
Correlation between serum triglyceride and cPLI concentrations in 195 miniature schnauzers. A significant positive correlation was seen between the two parameters (Spearman r=0.3215; P<0.0001).
Likelihood ratios for different serum triglyceride concentrations for serum cPLI concentrations consistent with pancreatitis (≥200 μg/L). The likelihood ratio remained between 1 and 2 for serum triglyceride concentrations <800 mg/dL. The likelihood ratio increased sharply for serum triglyceride concentrations >800 mg/dL. The lowest serum triglyceride concentration that produced a statistically significant likelihood for a cPLI ≥200 μg/L was 862 mg/dL.
Of the 195 dogs, 80 (41%) had serum triglyceride concentrations below the upper limit of the reference range, and these dogs were designated as group 1. The remaining 115 dogs had serum triglyceride concentrations above the upper limit of the reference range (>108 mg/dL) and were designated as group 2. Dogs in group 2 had a significantly higher median serum cPLI concentration (99.5 μg/L) than dogs in group 1 (39.3 μg/L; P=0.0001; Figure 3⇓). In addition, dogs in group 2 with very high serum triglyceride concentrations ≥862 mg/dL (as determined by ROC analysis) had significantly higher median serum cPLI concentrations (223.4 μg/L) than dogs in group 1 (P=0.0077; Figure 4⇓).
A statistically significant difference (P=0.0001) was seen in median serum cPLI concentrations between miniature schnauzers with normal serum triglyceride concentrations (≤108 mg/dL) and miniature schnauzers with serum triglyceride concentrations above the upper limit of the reference range (>108 mg/dL). The lines represent the median serum triglyceride concentration measured in each group. TG=triglycerides. Note: Y axis is split.
A statistically significant difference (P=0.0077) was seen in median serum cPLI concentrations between the group of miniature schnauzers with normal serum triglyceride concentrations (≤108 mg/dL) and miniature schnauzers with severely increased serum triglyceride concentrations (>862 mg/dL). The lines represent the median serum triglyceride concentration measured in each group. TG=triglycerides. Note: Y axis is split.
After excluding dogs with serum cPLI concentrations in the equivocal range (n=33), there were 75 dogs (instead of 80) with normal serum triglyceride concentrations and 87 dogs (decreased from 115) with hypertriglyceridemia. No significant difference was seen in the proportion of dogs with serum cPLI concentrations consistent with pancreatitis (i.e., ≥200 μg/L) between dogs with hypertriglyceridemia (29 of 87 dogs; 33.3%) and dogs with normal triglyceride concentrations (21 of 75 dogs; 28%; P=0.4986). However, 11 of the 87 dogs with hypertriglyceridemia had serum triglyceride concentrations ≥862 mg/dL. A statistically significant difference was seen in the proportion of dogs with serum cPLI concentrations consistent with pancreatitis (i.e., ≥200 μg/L) between the dogs with serum triglyceride concentrations ≥862 mg/dL (7 of 11 dogs; 63.6%) and dogs with serum triglyceride concentrations in the reference range (21 of 75 dogs; 28%; P=0.0343; odds ratio 4.5; 95% CI 1.2 to 17).
Discussion
Results of the present study suggest an association between serum triglyceride and cPLI concentrations in miniature schnauzers. Miniature schnauzers with hypertriglyceridemia had significantly higher serum cPLI concentrations than miniature schnauzers with normal serum triglyceride concentrations. In addition, miniature schnauzers with serum triglyceride concentrations ≥862 mg/dL were 4.5 times more likely to have serum cPLI concentrations consistent with pancreatitis (≥200 μg/L) than miniature schnauzers with normal serum triglyceride concentrations. Although previous studies have shown a frequent coexistence of hypertriglyceridemia and pancreatitis in dogs,11,27,28 the present study is the first to implicate the degree of hypertriglyceridemia as a possible cause of increased serum cPLI concentrations consistent with pancreatitis in miniature schnauzers.
A serum triglyceride concentration of 862 mg/dL was selected based on ROC analysis, and this concentration was associated with a more than threefold likelihood for having a serum cPLI concentration considered consistent with pancreatitis, compared to the likelihood for dogs with triglyceride concentrations ≤862 mg/dL. The likelihood ratio for having a serum cPLI concentration consistent with pancreatitis was often higher (up to 8.5 times higher) when higher serum triglyceride concentrations were selected [Figure 2⇑]. Increases of serum triglyceride concentrations ≥862 mg/dL are generally considered to be rather severe. Results of the present study suggest that the severity of hypertriglyceridemia is an important factor potentially affecting the likelihood for increased cPLI concentration consistent with pancreatitis in miniature schnauzers. Only severely increased serum triglyceride concentrations were associated with increased odds for an increased cPLI concentration consistent with pancreatitis in this breed. Mildly or moderately elevated serum triglyceride concentrations (i.e., <800 mg/dL) did not appear to represent a risk factor for a serum cPLI concentration suggestive of pancreatitis in this study. These findings are in agreement with studies in humans, in which only severe hypertriglyceridemia is recognized as a cause of pancreatitis.7,8 In humans, a serum triglyceride concentration >1000 mg/dL has been reported to be an identifiable risk factor for pancreatitis.8
In human patients, hypertriglyceridemia can either be the cause or the result of pancreatitis, and the same also has been suggested for dogs.8,10,27 When hypertriglyceridemia is the result of pancreatitis in humans, it is usually mild to moderate, whereas hypertriglyceridemia that causes pancreatitis is usually severe (typically ≥1000 mg/dL).8 In the present study, many dogs had serum triglyceride concentrations above the upper limit of the reference range, and it is possible that some of these dogs might have had hypertriglyceridemia secondary to pancreatitis rather than the opposite. This speculation, however, is not supported by the current literature. In one study where acute pancreatitis was experimentally induced in dogs, hypertriglyceridemia did not develop up to 96 hours after induction of pancreatitis.27 Similar results were reported in another study where pancreatitis was experimentally induced in dogs by ligation of the major and minor pancreatic ducts.29 In this latter reported study, pancreatitis did not result in hypertriglyceridemia or hypercholesterolemia up to 14 days after induction of pancreatitis.29 In a more recent study, mild increases in serum triglyceride concentrations were noted in dogs after induction of pancreatitis.30 Although serum triglyceride concentrations significantly increased, they remained within the reference range even after induction of pancreatitis.30 However, this was not clearly discussed in this report.30 Based on these three studies,27,29,30 it can be concluded that hypertriglyceridemia is not a feature of experimentally induced pancreatitis in dogs; however, it remains unknown whether this is also the case for spontaneous canine pancreatitis.
In an ongoing study of 56 dogs of different breeds (not including miniature schnauzers) with serum cPLI concentrations diagnostic for pancreatitis, only 14 (25%) had hypertriglyceridemia; of these, only one (1.8%) had a serum triglyceride concentration ≥862 mg/dL.d Collectively, the above data indicate that severe hypertriglyceridemia with triglyceride concentrations >862 mg/dL (which in this study showed a significant association with serum cPLI concentrations consistent with pancreatitis) appears unlikely to be the result of pancreatitis. Furthermore, in our clinical experience with miniature schnauzers, the vast majority of miniature schnauzers with pancreatitis and severe hypertriglyceridemia have preexisting hypertriglyceridemia, and most of them also have persistent hypertriglyceridemia even after recovery from pancreatitis, unless a low-fat diet is being offered.
Because of the high prevalence of idiopathic hypertriglyceridemia in miniature schnauzers,1 many of the dogs with elevated serum triglyceride concentrations enrolled in this study are likely to have this condition. Secondary causes of hypertriglyceridemia—mostly endocrinopathies such as diabetes mellitus, hyperadrenocorticism, and hypothyroidism—cannot be excluded as potential causes of the hypertriglyceridemia in these dogs.4 No evidence supports that the source (rather than the severity) of hypertriglyceridemia can affect the risk for pancreatitis, and severe hypertriglyceridemia of any cause (primary or secondary) should be considered a risk factor for high cPLI concentrations consistent with pancreatitis in miniature schnauzers.28 This is also the case in human patients, where severe hypertriglyceridemia secondary to other diseases (e.g., uncontrolled or untreated diabetes mellitus, diabetic ketoacidosis) has also been associated with pancreatitis.31,32
One limitation of the present study is the unavailability of the medical histories of the dogs enrolled. Because of this, the true disease status of each dog (e.g., whether the dog had clinical signs of pancreatitis) was unknown. However, the majority of samples submitted to our laboratory come from animals with gastrointestinal signs or suspected gastrointestinal disease. In addition, any concurrent conditions or medications administered cannot be excluded as factors contributing to the serum cPLI concentrations measured in this study. Important to note is that currently no known factors other than pancreatitis have been shown to increase serum cPLI concentrations ≥200 μg/L (the current cutoff value for pancreatitis).20,24,25 This study’s finding of an association between serum triglyceride and cPLI concentrations cannot be arbitrarily translated into an association between serum triglycerides and clinical pancreatitis, though such an association remains possible. To definitively make such a conclusion, further studies are needed to prospectively evaluate the risk for increased cPLI concentrations and pancreatitis in miniature schnauzers with hypertriglyceridemia. In addition, further studies are warranted to investigate the association between hypertriglyceridemia and pancreatitis in dogs of other breeds.
Conclusion
This is the first clinical study supporting an association between hypertriglyceridemia, especially severe hypertriglyceridemia (≥862 mg/dL), and increased serum cPLI concentrations consistent with pancreatitis (≥200 μg/L) in miniature schnauzers. Miniature schnauzers with severe hypertriglyceridemia (≥862 mg/dL) were 4.5 times more likely to have a serum cPLI concentration consistent with pancreatitis (≥200 μg/L) than were miniature schnauzers with a normal serum triglyceride concentration.
Footnotes
References
