Abstract
Objectives
To determine the clinical relevance of gallbladder sludge (GBS) in cats by assessing its association with neutrophilic cholangitis/cholangiohepatitis (NC/CH), bile culture results, serum biochemical abnormalities and ultrasonographic findings suggestive of pancreatitis or small intestinal thickening.
Methods
A retrospective review was performed on 166 cats that underwent percutaneous ultrasound-guided cholecystocentesis. Data collected included ultrasonographic presence of GBS, bile culture and cytology results, liver enzyme activities, total bilirubin concentration and final diagnosis of NC/CH. Statistical associations were evaluated using Fisher’s exact test and odds ratios (ORs).
Results
GBS was identified in 107/166 (64%) cats. There was no significant association between GBS and positive bile culture, bactibilia or NC/CH (P >0.84), nor with elevated alkaline phosphatase activity or total bilirubin (P >0.8). Cats with GBS were more likely to have normal alanine aminotransferase (ALT) activity compared with GBS-negative cats (OR 0.42; P = 0.025). Among GBS-positive cats, the presence of concurrent pancreatitis or intestinal thickening did not significantly increase the likelihood of NC/CH. A non-significant association was observed between elevated ALT activity and NC/CH in GBS-positive cats (OR 2.53; P = 0.135).
Conclusions and relevance
GBS is a frequent ultrasonographic finding in cats but does not reliably predict biliary infection or inflammation. These findings suggest that GBS should not be used in isolation to guide antimicrobial therapy or bile sampling. Clinical judgment and supporting diagnostic data remain essential in evaluating suspected hepatobiliary disease.
Plain language summary
Veterinarians often find gallbladder sludge during ultrasound examinations in cats. This sludge appears as thick material in the gallbladder and is sometimes suspected to be a sign of infection or liver disease. However, it has been unclear whether this finding alone means a cat is sick or needs treatment. In this study, we looked back at the medical records of 166 cats that had a procedure called a cholecystocentesis, where a small amount of bile is collected from the gallbladder using a needle guided by ultrasound. We reviewed the cats’ ultrasound reports, lab results and bile cultures to see if gallbladder sludge was linked to liver infection or other signs of disease. We found that gallbladder sludge was common, seen in 64% of cats, but it was not linked to a higher chance of infection in the bile or a diagnosis of cholangitis, which is inflammation of the liver and bile ducts. Cats with gallbladder sludge were also not more likely to have abnormal liver enzymes or bilirubin levels. Even when gallbladder sludge was present along with other ultrasound findings such as signs of pancreatitis or thickened intestines, there was no strong link to liver infection. These findings suggest that gallbladder sludge is often a harmless finding and should not be used by itself to decide whether a cat needs antibiotics or further liver testing. Instead, veterinarians should consider the overall clinical picture, including lab tests, clinical signs and bile culture results, before making treatment decisions.
Keywords
Introduction
Gallbladder sludge (GBS), characterized by gravity-dependent echogenic material within the gallbladder lumen, is a common ultrasonographic finding in cats. It has been reported in up to 40% of cats with hepatobiliary disease and in 20–62% of cats with extrahepatic biliary obstruction, raising questions about its clinical relevance and possible association with underlying pathology.1,2 In feline patients, the presence of GBS has been linked to positive bile cultures and cytologic findings consistent with neutrophilic cholangitis or cholangiohepatitis (NC/CH), suggesting a potential diagnostic role.1,3 However, other studies have proposed that GBS may be an incidental or non-specific finding, particularly in the absence of supporting clinicopathologic or microbiologic abnormalities.4,5
Feline cholangitis,6,7 particularly the neutrophilic subtype, frequently occurs alongside concurrent inflammatory conditions such as pancreatitis and chronic enteropathy. This overlap – commonly referred to as ‘triaditis’ – is thought to reflect the close anatomical and functional interconnection of the biliary tract, pancreas and gastrointestinal system. 8 Ultrasonographic findings such as pancreatic changes or intestinal muscularis thickening are often used clinically to support a suspicion of multisystemic inflammatory disease; however, the diagnostic utility of these findings in predicting NC/CH remains unclear. 9
Percutaneous ultrasound-guided cholecystocentesis (PUC) is a minimally invasive procedure that allows direct sampling of bile for cytology and culture. In veterinary medicine, PUC plays a critical role in confirming bacterial cholangitis and guiding antimicrobial therapy decisions.10–12 Yet, there is limited information regarding the diagnostic performance of bile cytology and culture relative to ultrasonographic indicators such as GBS, especially in the context of concurrent pancreatitis or gastrointestinal abnormalities.13,14
Building on prior studies, this retrospective analysis explored the clinical relevance of gallbladder sludge in cats undergoing PUC, using a distinct study design and population to assess associations with cytologic, culture and clinicopathologic findings. We hypothesized that GBS would be associated with a higher likelihood of NC/CH, particularly when accompanied by ultrasonographic evidence of concurrent pancreatitis and/or small intestinal thickening (SIT). Specifically, this study aimed to determine the prevalence of GBS and its association with bile culture and cytology results, assess the relationship between GBS and ultrasonographic findings such as pancreatitis and intestinal muscularis thickening, compare liver enzyme activities and total bilirubin concentrations between cats with and without GBS, and evaluate whether the combination of GBS and biochemical or ultrasonographic abnormalities is predictive of NC/CH.
Materials and methods
Case selection
Feline patients that underwent PUC at Washington State University between June 2015 and August 2024 were identified by retrospective review of the medical record database (Figure 1). Search terms used to identify cases included ‘cholecystocentesis’, ‘biliary aspirate/aspiration’, ‘gallbladder aspirate/aspiration’, ‘gallbladder’ and ‘biliary centesis’. Medical records of all cats that underwent PUC were reviewed. To ensure the relevance of ultrasound findings to bile sampling, only cases in which a complete abdominal ultrasound examination was performed within 24 h before the ultrasound-guided cholecystocentesis were included.
Flow diagram of study enrollment and classification of cats. A total of 175 cats underwent percutaneous ultrasound-guided cholecystocentesis between June 2015 and August 2024. Nine cases were excluded because of incomplete records or failure to meet inclusion criteria, resulting in 166 cats being included in the final analysis. Cats were categorized by the presence or absence of gallbladder sludge on abdominal ultrasonography. Each group was further stratified by the diagnosis of NC/CH, as determined by cytology and/or positive bile culture, and by the presence of concurrent ultrasonographic findings, including pancreatitis and intestinal muscularis thickening. NC/CH = neutrophilic cholangitis/cholangiohepatitis
Data collection
For each case enrolled in the study, data obtained included signalment (age, breed, sex), presenting complaint, ultrasonographic findings of the liver, gallbladder, pancreas and gastrointestinal tract, and serum alanine aminotransferase (ALT), alkaline phosphatase (ALP), total bilirubin, bile bacterial culture and/or cytology results. Age was approximated to the closest year at the time of presentation. Additional data collected included the following: working or final diagnosis; hepatic cytology; reported immediate complications from PUC; and serum pancreatic lipase immunoreactivity (spec fPLI) results. Evidence of attempted antibiotic therapy before PUC and past pertinent history was sought when available.
Ultrasonography and ultrasound-guided sample collection
All abdominal ultrasound examinations and ultrasound-guided procedures were performed by a board-certified veterinary radiologist or a radiology resident using an ultrasound system with transducer frequencies in the range of 5–10 MHz on older units or 4.2–10 Mhz (VetGE LOGIQ E10). Ultrasound examination reports were reviewed for the presence of gravity-dependent, echogenic debris (ie, GBS), SIT and pancreatitis. PUC was performed aseptically using a 23 G or 25 G 1.5 inch needle attached to a 10 ml syringe. Immediate complications associated with PUC documented by the radiologist at the time of the procedure were recorded. Fine-needle aspiration of the liver and other sites (if applicable) was performed using a 23 G or 25 G needle; whether an aspirate was obtained using negative pressure was not recorded.
Cytology and bile bacterial culture
All cytology specimens were stained with Wright–Giemsa stain and examined by a board-certified veterinary clinical pathologist and a pathology resident. Bile samples were submitted to Washington Animal Disease Diagnostic Laboratory for aerobic and anaerobic culture. Cultures were examined daily for bacterial growth for 7 days. Antimicrobial susceptibility results for aerobic bacteria were recorded.
Case classification
The main inclusion criteria for cases of NC in this study were a positive bacterial culture of bile and/or the presence of bacteria (ie, bactibilia) on bile cytology. 15 An additional criterion for the presumed diagnosis of neutrophilic cholangiohepatitis (NCH) was the presence of neutrophilic inflammation on hepatic cytology without reported overt evidence of blood contamination.13,16
In this study, pancreatitis was inferred based on ultrasonographic findings consistent with pancreatitis as reported by the radiologist, and, when available, an elevated serum spec fPLI concentration. Ultrasonographic abnormalities consistent with pancreatitis included increased echogenicity of the surrounding mesentery, irregular pancreatic margins, dilation of the pancreatic duct, hyperechoic or hypoechoic pancreas, nodularity and pancreatic enlargement.11,17 Spec fPLI concentrations greater than 3.5 µg/l were considered elevated, with values in the range of 3.6–5.4 µg/l classified as equivocal. Only cases with a spec fPLI concentration of 5.4 µg/l and above were considered consistent with pancreatitis and included in the analysis. 18
The inclusion criteria for ultrasonographic evidence of SIT required radiologist-reported diffuse thickening of the muscularis propria, submucosa or mucosa of the small intestine (duodenum, jejunum and/or ileum). 9 Gallbladder wall (GBW) thickening was defined as a wall thickness greater than 1 mm, as reported by the interpreting radiologist; exact measured values were not reviewed in this study.
Statistical analysis
Data were tabulated using Excel version 16.5 (Microsoft Corp). All continuous data were assessed for normality using the Shapiro–Wilk test, histogram and quantile–quantile plot. Continuous data were presented as median and range, while categorical data were presented as percentages. Categorical variables were compared using Fisher’s exact test. Statistical analysis was performed using the commercially available software GraphPad Prism version 10.3 and the significance level for all tests was set at 5%.
Results
Study population
A total of 175 cats were initially identified for review. Nine cats were excluded because of incomplete medical records, leaving 166 cases that met the inclusion criteria for final analysis. This data set included three cats that underwent PUC on two separate occasions, each at least 3 months apart and associated with distinct clinical presentations. These were analyzed as independent cases. Descriptive statistics are summarized in Table 1. The cohort included 86 (51.8%) male cats (85 castrated, one intact) and 80 (48.2%) female cats (79 spayed, one intact). The median age was 10 years (range 1–18). Domestic shorthair was the most common breed (n = 113, 68.1%), followed by domestic longhair (n = 24, 14.5%), domestic medium hair (n = 13, 7.8%) and Bengal (n = 5, 3.0%). Additional breeds included two each of Maine Coon mix, Russian Blue, Abyssinian and Sphynx, and one each of Siamese, Exotic Shorthair and Norwegian Forest Cat.
Signalment characteristics of cats with and without gallbladder sludge (GBS)
Data are n (%) or median (range)
Of the 166 cats included in this analysis, 107 (64%) had ultrasonographic evidence of GBS and 59 did not. Descriptive statistics comparing cats with or without GBS are summarized in Table 1. There was no statistically significant association between signalment (age, sex or breed) and GBS status (P >0.05).
Pancreatic ultrasound and spec fPLI assay results
Of the 166 cases reviewed, 20 (12%) were reported to have ultrasonographic findings consistent with pancreatitis. Spec fPLI results were available for 81 cases, of which 19 had an elevated serum feline pancreatic lipase (fPL) concentration (⩾5.4 µg/l). When combining both diagnostic modalities, a total of 39 (23%) cases met the criteria for pancreatitis. Notably, 17 cases with elevated serum fPL concentrations were not identified as having pancreatitis based on ultrasound examination findings, while five cases with ultrasonographic evidence of pancreatitis had normal or equivocal serum fPL concentrations.
Complications associated with PUC
An immediate complication from PUC was reported in a single case, in which a small volume of abdominal effusion was noted immediately after the procedure. The effusion was not aspirated for fluid analysis; therefore, it was unclear whether it represented hemorrhage or bile leakage. This cat did not have GBS but exhibited mild GBW thickening before PUC.
Association between GBS and liver enzyme abnormalities
Serum ALT activity was elevated in 110/166 (66%) cats, including 64/107 (60%) GBS-positive cats and 46/59 (78%) GBS-negative cats (Table 2). This difference was statistically significant (Fisher’s exact test, P = 0.025). The odds ratio (OR) was 0.42 (95% confidence interval [CI] 0.20–0.87), suggesting a potential association between GBS status and ALT activity in this population. Specifically, cats with GBS were more likely to have normal ALT activity compared with those without GBS.
Associations between gallbladder sludge (GBS) status and biochemical, microbiologic and ultrasonographic findings in cats
Data are n (%) or OR (95% CI)
P <0.05 is significant
= present; – = absent; ALP = alkaline phosphatase; ALT = alanine aminotransferase; CI = confidence interval; fPLI = pancreatic lipase immunoreactivity; NC/CH = neutrophilic cholangitis/cholangiohepatitis; OR = odds ratio; SIT = small intestinal thickening; US = ultrasonography
Serum ALP activity was elevated in 76/166 (46%) cats. Among cats with GBS, 48/107 (45%) had elevated ALP, compared with 28/59 (47%) GBS-negative cats. The difference in elevated ALP activity between groups was not statistically significant (Fisher’s exact test, P = 0.871). The OR was 0.9 (95% CI 0.48–1.70), indicating no meaningful association between the presence of GBS and elevated ALP activity.
Total bilirubin was elevated in 70/166 (42%) cats. Among cats with GBS, 45/107 (42%) had elevated total bilirubin, compared with 25/59 (42%) in the GBS-negative group. There was no statistically significant association between the presence of GBS and total bilirubin levels (Fisher’s exact test, P >0.9999). The OR was 0.99 (95% CI 0.52–1.88), indicating no difference in the likelihood of bilirubin elevation between cats with and without GBS.
Across all comparisons – including ALT, ALP and total bilirubin – only the association between GBS and serum ALT activity reached statistical significance. These findings suggest that GBS status may serve as a potential marker for serum ALT activity in cats, with GBS-negative cats more likely to exhibit elevated ALT levels.
Association between GBS and NC/CH
Among GBS-positive cats, 18/107 (16.8%) were culture- or bactibilia-positive and classified as having NC, compared with 10/59 (17.0%) GBS-negative cats (Table 2). There was no statistically significant association between the presence of GBS and a positive bile culture or bactibilia (Fisher’s exact test, P >0.9999). The calculated OR was 0.991 (95% CI 0.45–2.31), indicating no meaningful difference in likelihood between groups. Similar findings were observed when all cases of NC/CH were considered: there was no significant association with GBS status (Fisher’s exact test, P = 0.841) and the OR was 0.86 (95% CI 0.40–1.88).
Association between biochemical markers and NC/CH in GBS-positive cats
Among cats with GBS, those with elevated ALT activity were more likely to be diagnosed with NC/CH than those with normal ALT (16/64 [25%] vs 5/43 [12%], respectively) (Table 3). Although this difference did not reach statistical significance (Fisher’s exact test, P = 0.135), the trend was notable. The OR was 2.53 (95% CI 0.85–7.54), suggesting a potential association between elevated ALT in GBS-positive cats and the presence of NC/CH.
Association between clinicopathologic and ultrasonographic findings and neutrophilic cholangitis/cholangiohepatitis in cats with gallbladder sludge (GBS)
All cases of pancreatitis
ALP = alkaline phosphatase; ALT = alanine aminotransferase; SIT = small intestinal thickening
Similarly, among GBS-positive cats, NC/CH was diagnosed in 11/45 (23%) cats with elevated ALP activity, compared with 10/60 (16%) cats with normal ALP activity. This difference was not statistically significant (Fisher’s exact test, P = 0.465), but the OR of 1.53 (95% CI 0.59–3.98) indicates a possible trend toward increased risk that warrants further investigation.
In GBS-positive cats, 10/45 (20%) with elevated total bilirubin were diagnosed with NC/CH, compared with 11/62 (18%) with normal bilirubin levels. This difference was not statistically significant (Fisher’s exact test, P = 0.626) and the OR was 1.32 (95% CI 0.51–3.45), indicating a non-significant trend toward an increased likelihood of NC/CH in cats with hyperbilirubinemia.
Association between GBS and GBW thickening
GBW thickening was reported in 18 (11%) cats, including 12/107 (11%) GBS-positive cats and 6/59 (10%) GBS-negative cats (Table 2). This difference was not statistically significant (Fisher’s exact test, P >0.9999), indicating no association between GBS status and GBW thickening in this population.
Among cats with GBW thickening, 12 (66%) were diagnosed with NC/CH. This represented a statistically significant association (Fisher’s exact test, P <0.0001) with an OR of 11.45 (95% CI 3.75–35.60), indicating a markedly increased likelihood of NC/CH in cats with GBW thickening.
Pancreatitis and SIT, and association with NC/CH in GBS-positive cats
Among GBS-positive cats, the presence of concurrent ultrasonographic findings of either pancreatitis or SIT was not significantly associated with a diagnosis of NC/CH (Table 3). Of the 25 cats with GBS and pancreatitis, 10 had concurrent SIT and 15 did not. NC/CH was diagnosed in 3/10 (30%) cats with SIT and 5/15 (33.3%) without SIT. There was no statistically significant difference between groups (Fisher’s exact test, P >0.9999; OR 0.86, 95% CI 0.18–4.22), suggesting that concurrent SIT and pancreatitis do not meaningfully modify the likelihood of NC/CH in GBS-positive cats.
Culture and cytology results
Bile culture was performed in 142/166 cases, yielding positive results in 26 (18%) cases (Table 4). All but one sample underwent both aerobic and anaerobic culture. A total of 37 bacterial isolates were recovered (Table 5), with monomicrobial growth identified in 19/26 samples (73%) and mixed-microbial growth in 7/26 samples. The most frequently cultured isolate was Enterococcus species (11/37, 30%), followed by Escherichia coli (6/37, 16%). Of the 142 cases in which bile was submitted for culture, 129 also had bile cytology performed. An additional 24 cases were submitted for bile cytology only. A total of 28 cases met the inclusion criteria for NC, based on a positive bacterial culture and/or the presence of bactibilia.
Summary of bile culture submissions and results in cats (2015–2024)
Data are n (%)
One bile sample was submitted for aerobic culture only
Distribution of bacterial isolates from bile samples in cats undergoing cholecystocentesis
Data are n (%)
Liver cytology was performed in 130/166 cases. Among these, six cases with negative bile culture and no evidence of bactibilia demonstrated neutrophilic inflammation on liver cytology and were classified as NCH. In total, 34 cases were classified as having NC/CH.
Discussion
This retrospective study evaluated the presence of GBS in cats undergoing PUC and found no significant association between GBS and positive bile culture, NC/CH or most serum biochemical abnormalities. These findings challenge the clinical assumption that GBS is a reliable marker of infectious or inflammatory hepatobiliary disease in cats.
GBS was present in 64% of cases, consistent with previous reports that it is a common ultrasonographic finding in cats with hepatobiliary disease. However, in the present study, GBS was not significantly associated with bile culture positivity, bactibilia, NC/CH or GBW thickening, in contrast to prior work reporting increased odds of GBS in cats with GBW thickening. 2 This discrepancy may reflect differences in sample size, study population or timing of data collection. Notably, GBW thickening in our cohort was significantly associated with NC/CH, aligning with previous studies1,5 linking GBW thickening to a higher likelihood of positive bile cultures in cats with suspected hepatobiliary disease. These findings suggest that GBS may often be incidental or non-specific, and that its ultrasonographic detection alone should not be used to guide antimicrobial therapy or further diagnostic investigation.1,10
Serum ALT and ALP activity and total bilirubin concentrations did not differ significantly between GBS-positive and GBS-negative cats, except for ALT, which was paradoxically more frequently elevated in cats without GBS. Although a trend toward increased NC/CH was observed among GBS-positive cats with elevated ALT, the difference did not reach statistical significance. These findings underscore the limited utility of biochemical markers alone in predicting biliary infection and highlight the potential influence of concurrent disease processes such as pancreatitis or inflammatory bowel disease.3,8,19
Among GBS-positive cats, the presence of ultrasonographic signs of pancreatitis or SIT did not significantly increase the likelihood of NC/CH. This aligns with previous research indicating that these features, although suggestive of ‘triaditis’, 8 are non-specific and should be interpreted cautiously. The muscularis layer thickening often seen in chronic enteropathies or lymphoma may further complicate interpretation. 9
Notably, several cats without GBS had positive bile cultures or evidence of bactibilia, suggesting that clinicians should not rely on gallbladder appearance alone to determine whether to pursue bile sampling. Our findings support the continued use of PUC when clinical suspicion is high, even in the absence of classic ultrasonographic abnormalities.10–12 Although PUC is minimally invasive and generally well tolerated, 12 sampling should be guided by clinical context rather than imaging findings alone.
In our cohort, 18% of bile cultures were positive – lower than the positive rates of 35–36% previously reported in similar feline studies.1,3 This may reflect differences in case selection or technical variables, such as bile volume submitted, prior antimicrobial exposure or culture methods. Similar to previous studies, Enterococcus species and E coli were the most commonly isolated organisms,1,3,15 and monomicrobial infections predominated. These findings support the generalizability of our microbiological results.
Although histopathology remains the gold standard for diagnosing pancreatitis, it is rarely feasible in clinical settings because of its invasive nature. Its diagnostic utility is further limited by the multifocal distribution of pancreatic lesions and the possibility of detecting subclinical disease. No single diagnostic modality achieves 100% sensitivity and specificity; therefore, ante-mortem diagnosis generally relies on a combination of clinical history, physical examination, pancreatic-specific serologic testing and diagnostic imaging. Serum spec fPLI is a well-validated biomarker for feline pancreatitis, with a diagnostic cutoff of 5.4 µg/l and above shown to optimize accuracy. 20 Ultrasonography remains the most widely used imaging modality for evaluating feline pancreatitis, although its reported sensitivity and specificity have historically varied. More recent studies report sensitivities of 62–80%, likely reflecting advances in ultrasound technology and operator proficiency. 21 Given the retrospective nature of the present study, patient history and clinical signs were not assessed, as they were outside the primary scope of investigation. For this study, pancreatitis was inferred from ultrasonographic findings and, when available, elevated serum spec fPLI concentrations. The authors acknowledge the limitations of both ultrasonography and spec fPLI in diagnosing feline pancreatitis and recognize that, in the absence of histopathology and clinical context, a definitive diagnosis cannot be established.
This study is subject to the inherent limitations of retrospective design, including incomplete records and variability in diagnostic investigations. Cases undergoing PUC may have been pre-selected based on clinical suspicion, introducing potential selection bias. The volume of bile submitted for culture was not standardized and may have contributed to false negatives. In addition, prior antimicrobial administration was not consistently documented. Some cases underwent cytology without culture, possibly leading to underestimation of the prevalence of bacterial disease. Furthermore, the diagnostic accuracy of liver cytology in detecting inflammatory disease is variable and influenced by sampling quality, neutrophilic infiltrates from peripheral blood and the absence of histologic confirmation.13,16,22,23
These findings argue against initiating antimicrobial therapy based solely on the presence of GBS. As veterinary medicine increasingly prioritizes antimicrobial stewardship, identifying reliable and specific indications for bile sampling and treatment is essential. 24 PUC remains a valuable diagnostic procedure when guided by clinical suspicion; however, routine sampling based solely on ultrasonographic evidence of sludge is not supported by the findings of this study.
Conclusions
GBS was a common ultrasonographic finding but was not associated with bile culture positivity, NC/CH, or elevations in liver enzyme activities or bilirubin. Concurrent findings, such as pancreatitis or intestinal thickening, did not increase the likelihood of NC/CH in GBS-positive cats. These results suggest that GBS is a non-specific finding and should not alone prompt antimicrobial therapy or bile sampling without supporting clinical evidence.
Footnotes
Conflict of interest
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.
Ethical approval
The work described in this manuscript involved the use of non-experimental (owned or unowned) animals. Established internationally recognized high standards (‘best practice’) of veterinary clinical care for the individual patient were always followed and/or this work involved the use of cadavers. Ethical approval from a committee was therefore not specifically required for publication in JFMS. Although not required, where ethical approval was still obtained, it is stated in the manuscript.
Informed consent
Informed consent (verbal or written) was obtained from the owner or legal custodian of all animal(s) described in this work (experimental or non-experimental animals, including cadavers, tissues and samples) for all procedure(s) undertaken (prospective or retrospective studies). No animals or people are identifiable within this publication, and therefore additional informed consent for publication was not required.
