Histopathology and Feline Pancreatic Lipase Immunoreactivity in Inflammatory, Hyperplastic and Neoplastic Pancreatic Diseases in Cats

Clinical enzymology of the dog and cat

Clinical enzymology studies the enzyme activity in serum or other body fluids for the diagnosis, prognosis or monitoring of a variety of diseases. Clinical enzymology has greatly benefited from advances in technology and is now an integral part of laboratory analysis. However, to maximise the clinical benefits of serum enzyme measurement, clinicians and clinical pathologists must have a good understanding of the pathophysiology behind serum enzyme alterations. They must also be aware of the preanalytical and analytical factors that can affect the accuracy of serum enzyme activity measurement. This review article first covers the basic concepts of clinical enzymology and the general mechanisms related to serum enzyme alterations. Then, the review discusses the potential effects of various preanalytical and analytical factors on enzyme activity measurement. Lastly, it explores the pathophysiology and clinical use of various serum enzymes in canine and feline medicine. The present review article aims to be a comprehensive one-stop source for clinical pathologists and small animal practitioners.

Analytical validation of an ELISA for the measurement of feline pancreas-specific lipase and re-evaluation of the reference interval and decision threshold for diagnosing pancreatitis

BACKGROUND

The diagnosis of feline pancreatitis can be challenging. The clinical presentation often includes mild, nonspecific clinical signs, such as vomiting, anorexia, and weight loss. Measurement of feline pancreatic lipase immunoreactivity (fPLI) concentration in serum has been reported to be sensitive and specific for a diagnosis of pancreatitis in cats. However, analytical validation for a widely available commercial assay for the measurement of fPLI concentration has not been published.

OBJECTIVE

We aimed to analytically validate the Spec fPL assay (IDEXX Laboratories, Westbrook, ME), a commercial ELISA for the measurement of fPLI concentration, and re-evaluate its reference interval and decision threshold for diagnosing pancreatitis in cats.

METHODS

Dilutional linearity, accuracy, precision, and the effect of interfering substances were assessed. The upper limit of the reference interval was calculated based on the 95th percentile of results from clinically healthy cats (n = 107), and a decision threshold for diagnosing pancreatitis was calculated with an expected specificity of 99%.

RESULTS

Analytical validation demonstrated good linearity, accuracy, and precision, as well as the absence of interference from lipemia, hemolysis, or icterus. The upper limit of the reference interval for Spec fPL was determined to be 4.4 μg/L, and the decision threshold (a theoretical cut-off) for diagnosing pancreatitis was determined to be 8.8 μg/L based on a desired specificity of 99%.

CONCLUSIONS

The Spec fPL assay is analytically valid, and results suggest that a decision threshold of 8.8 μg/L would have high diagnostic specificity for excluding clinically healthy cats.

Contrast-enhanced ultrasound features of focal pancreatic lesions in cats

A large overlap in the ultrasound (US) features of focal pancreatic lesions (FPLs) in cats is reported. Furthermore, only a small number of studies describing the contrast-enhanced ultrasound (CEUS) features of FPLs in cats have been conducted today. The aim of this study is to describe the B-mode US and CEUS features of FPLs in cats. Ninety-eight cats cytologically diagnosed with FPL were included. The lesions were classified as adenocarcinoma (n = 40), lymphoma (n = 11), nodular hyperplasia (n = 17), other benign lesion (OBL) (n = 20), cyst (n = 4) or other malignant lesion (OML) (n = 6). Several qualitative and quantitative B-mode and CEUS features were described in each case. OMLs and cysts were not included in the statistical analysis. A decision tree to classify the lesions based on their B-mode and CEUS features was developed. The overall accuracy of the cross-validation of the decision tree was 0.74 (95% CI: 0.63–0.83). The developed decision tree had a very high sensitivity and specificity for nodular hyperplasia (1 and 0.94, respectively) as well as good sensitivity and specificity for both adenocarcinomas (0.85 and 0.77, respectively) and OBLs also (0.70 and 0.93, respectively). The algorithm was unable to detect any specific feature for classifying lymphomas, and almost all the lymphomas were classified as adenocarcinomas. The combination between CEUS and B-mode US is very accurate in the classification of some FPLs, especially nodular hyperplasia and adenocarcinomas. Cytopathology and or histopathology is still a fundamental step FPL diagnostic workflow.

Accuracy of acute-phase proteins in identifying lethargic and anorectic cats with increased serum feline pancreatic lipase immunoreactivity

The mainstay of laboratory diagnostics of feline pancreatitis (FP) is measuring serum feline pancreatic lipase immunoreactivity (fPLI). Thus far, several studies have investigated the relationship between acute-phase proteins (APPs) and the presence and severity of FP. Although changes in serum amyloid A (SAA) concentration have been linked with FP, its diagnostic accuracy remains unknown. We aimed to determine the accuracy of selected APPs in identifying cats with a high risk of FP based on increased fPLI. Serum fPLI was measured in cats (n = 52) that were presented to veterinary clinics with signs of lethargy and anorexia. The cats were divided into two groups (fPLI ≤3.5 μg/L; n = 27 and fPLI >3.5 μg/L, n = 25), corresponding to low and high risks of FP. Serum albumin, globulin, haptoglobin (Hp), and SAA concentrations, as well as the albumin-to-globulin ratio (A/G) and SAA-to-albumin (SAA/A) ratios, were determined and compared between groups. The accuracy of these measurements was examined using a multivariable logistic regression model and receiver operator characteristic (ROC) curve analysis. SAA concentrations and SAA/A ratios were significantly (P = .026 and P = .022) higher in cats with increased fPLI, with the area under ROC curve (AUROC) of 68.1% (CI 95%: 53.4%, 82.9%) and 68.6% (CI 95%: 54.0%, 83.2%), respectively. The logistic regression model combining SAA and A/G had AUROC of 75.2% (CI 95%: 62.0%, 88.4%) for identifying cats with increased fPLI. SAA as a sole analyte or combined with A/G had low to moderate accuracy in identifying anorexic, lethargic cats with increased fPLI. Serum albumin, globulin, and Hp concentrations had no discriminatory potential in these cats.

Correlation between metabolomic profile constituents and feline pancreatic lipase immunoreactivity

Background

Feline pancreatic lipase immunoreactivity (fPLI) is commonly used to diagnose pancreatitis in cats (FP). Untargeted metabolomics has been extensively applied in human and veterinary medicine, but no metabolomic studies regarding FP have been conducted.

Objectives

To identify metabolites significantly associated with increased fPLI.

Animals

Forty‐nine client‐owned cats: 11 clinically healthy and 38 with various clinical conditions.

Methods

Analytical cross‐sectional study with convenience sampling. A panel of 630 metabolites belonging to 26 biochemical classes was quantified in plasma using a commercial metabolomic assay. The correlation between plasma metabolite concentrations and serum fPLI was evaluated using Spearman's rank correlation coefficient (R_s) with Bonferroni correction. Multivariable analysis then was performed to control for glomerular filtration rate, liver damage, and blood glucose concentration. The accuracy of selected metabolites in discriminating between cats with normal (≤3.5 μg/L) and increased (>5.3 μg/L) fPLI was estimated using the area under the receiver operating characteristic curve (AUROC).

Results

Four hundred and seven of 630 metabolites (64.6%) were quantified in all cats. When controlled for potential confounders only 3 sphingolipids were significantly positively correlated with fPLI: 2 cerebrosides: HexCer(d18:1/24:0); (R_s = .56), and HexCer(d18:1/24:1); (R_s = .58) and 1 sphingomyelin: SM C18:0 (R_s = .55). Their AUROCs in identifying cats with increased fPLI were 82% (95% confidence interval [CI 95%], 70%‐94%), 84% (CI 95%, 72%‐96%), and 78% (CI 95%, 65%‐92%), respectively.

Conclusions and Clinical Importance

Selected sphingolipids are moderately positively correlated with fPLI and appear to have fair to moderate diagnostic accuracy in discriminating between cats with normal and increased fPLI.

Application of a complete blood count to screening lethargic and anorectic cats for pancreatitis

Background

Feline pancreatitis (FP) is an important health problem of cats. Its diagnostics is based on the combination of quantification of serum pancreatic lipase immunoreactivity (fPLI) and abdominal ultrasonography (AUS). These modalities allow for establishing highly specific diagnosis, however they are relatively expensive and time-consuming. On the other hand, a screening test of high sensitivity which would allow to rule out FP on the first visit without a considerable increase of costs would be clinically useful. To evaluate accuracy of nonspecific inflammatory biomarkers based on complete blood count (CBC) in diagnosing FP 73 client-owned cats with signs of lethargy and reduced appetite lasting for at least 2 days before presentation were enrolled in the cross-sectional study. They were examined with fPLI assay and AUS and classified as cats with very low risk of FP when fPLI ≤3.5 μg/L and AUS negative for FP, or as cats with increased risk of FP in the case of any other combination of results. Then, 7 various CBC measurements were measured in each cat and linked to the risk of FP using the multivariable logistic regression.

Results

Five CBC measurements turned out to be significantly associated with the risk of FP – total leukocyte count (WBC; crude odds ratio(OR_crude) = 12.2; CI 95%: 1.52, 98.5), total neutrophil count (OR_crude = 5.84; CI 95%: 1.22, 27.9), band neutrophil count (BNC; OR_crude = 6.67; CI 95%: 1.98, 22.4), neutrophil-to-lymphocyte ratio (OR_crude = 3.68; CI 95%: 1.25, 10.9), and eosinophil count (EC; OR_crude = 0.34; CI 95%: 0.12, 0.96). The model based on WBC, BNC, and EC proved to have at least fair diagnostic potential (area under ROC curve 82.7%; CI 95%: 72.8%, 92.5%). When WBC <  18 G/L, BNC <  0.27 G/L, and EC >  0.3 G/L was considered as a negative result, and any other combination as the positive result, the CBC model had high sensitivity (91.8%; CI 95%: 80.8%, 96.8%) at a relatively low specificity (58.3%; CI 95%: 38.8%, 75.5%).

Conclusion

The combination of three CBC measurements is an immediately available and fairly accurate screening method for identification of lethargic and anorectic cats with increased risk of FP.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-021-03098-z.

The Agreement between Feline Pancreatic Lipase Immunoreactivity and DGGR-Lipase Assay in Cats-Preliminary Results

Simple Summary

Feline pancreatitis is a common disease with diagnostics requiring a combination of clinical, laboratory and imaging methods. Measuring of pancreatic lipase concentration is the laboratory mainstay of feline pancreatitis diagnostics. It can be done using immunoenzymatic assay (feline pancreatic immunoreactivity, fPLI) or colorimetric assay based on hydrolyzing a special substrate (DGGR) to a color product. A DGGR-lipase assay is manufactured by various companies. Studies carried out in cats on the DGGR-lipase assay of a single manufacturer have shown a high agreement with fPLI, however studies in dogs indicate that the performance of assays of different manufacturers may vary considerably. One of the largest Polish veterinary laboratories working 24/7 in the largest Polish cities offers the DGGR-lipase assay of a large Polish laboratory solutions provider. The values obtained in this assay are higher than those yielded by the traditional DGGR-lipase assay validated in studies carried out so far. Therefore, we decided to evaluate the agreement between the DGGR-lipase assay of the Polish manufacturer and fPLI. The agreement proved to be as high as for the traditional assay.

Abstract

The colorimetric catalytic assay based on the use of 1,2-o-dilauryl-rac-glycero-3-glutaric acid-(6′-methylresorufin) (DGGR) ester as a substrate for pancreatic lipase activity is commonly used for the diagnosis of pancreatitis in dogs and cats. Even though the assay has generally been shown to yield consistent results with feline pancreatic lipase immunoreactivity (fPLI) assay, the agreement may vary between assays of different manufacturers. In this study, the chance-corrected agreement between a DGGR-lipase assay offered by one of the biggest providers of diagnostic solutions in Poland and fPLI assay was investigated. The study was carried out on 50 cats in which DGGR-lipase activity and fPLI were tested in the same blood sample. The chance-corrected agreement was determined using Gwet’s AC₁ coefficient separately for the fPLI assay’s cut-off values of >3.5 μg/L and >5.3 μg/L. The DGGR-lipase activity significantly positively correlated with fPLI (R_s = 0.665; CI 95%: 0.451, 0.807, p < 0.001). The chance-corrected agreement between the fPLI assay and DGGR-lipase assay differed considerably depending on the cut-off values of the DGGR-lipase assay. When the cut-off value reported in the literature (>26 U/L) was used, it was poor to fair. It was moderate at the cut-off value recommended by the laboratory (>45 U/L), and good at the cut-off value recommended by the assay’s manufacturer (>60 U/L). The highest agreement was obtained between the fPLI assay at the cut-off value of 3.5 μg/L and the DGGR-lipase assay at the cut-off value of 55 U/L (AC₁ = 0.725; CI 95%: 0.537, 0.914) and between the fPLI assay at the cut-off value of 5.3 μg/L and the DGGR-lipase assay at the cut-off value of 70 U/L (AC₁ = 0.749; CI 95%: 0.577, 0.921). The study confirms that the chance-corrected agreement between the two assays is good. Prospective studies comparing both assays to a diagnostic gold standard are needed to determine which of them is more accurate.

Clinical and Pathological Data of 17 Non-Epithelial Pancreatic Tumors in Cats

Tumors of mesenchymal origin are rarely reported in the pancreas. Therefore, this study characterized 17 feline non-epithelial pancreatic tumors, including clinical data, histopathology, and immunohistochemistry. Seventeen feline pancreatic tissue samples were investigated histopathologically and immunohistochemically. Selected pancreatic and inflammatory serum parameters, e.g., feline pancreatic lipase immunoreactivity (fPLI), 1,2-o-dilauryl-rac-glycero-3-glutaric acid-(6'-methylresorufin) ester (DGGR) lipase and serum amyloid A (SAA), were recorded, when available. The neoplasms were characterized as round (n = 13) or spindle (n = 4) cell tumors. Round cell tumors included 12 lymphomas and one mast cell tumor in ectopic splenic tissue within the pancreas. Lymphomas were of T-cell (n = 9) or B-cell (n = 3) origin. These cats showed leukocytosis (3/3) and increased fPLI (5/5), DGGR lipase (3/5) and SAA (4/5) values. Spindle cell tumors included two hemangiosarcomas, one pleomorphic sarcoma and one fibrosarcoma. The cat with pleomorphic sarcoma showed increased SAA value. Overall survival time was two weeks to seven months. These are the first descriptions of a pancreatic pleomorphic sarcoma and a mast cell tumor in accessory spleens within feline pancreas. Although rare, pancreatic tumors should be considered in cats presenting with clinical signs and clinical pathology changes of pancreatitis. Only histopathology can certainly distinguish solitary pancreatitis from a neoplasm with inflammation.