Reference Values for Gallbladder Ejection Fraction in a Healthy Indian Cohort Using Fatty Meal Hepatobiliary Scintigraphy

Introduction

The standard method for evaluating gallbladder ejection fraction (GBEF) is through dynamic hepatobiliary scintigraphy, using synthetic cholecystokinin (sincalide) to stimulate gallbladder contraction.[12] While widely accepted, this method has notable drawbacks: (1) limited availability of sincalide, (2) nonphysiological pharmacodynamics due to the use of higher-than-normal doses of sincalide, and (3) the potential for patient discomfort due to side effects such as abdominal cramping and nausea.[3] Furthermore, the procedure requires patients to lie under a scanner for a continuous 60 min, which can be inconvenient.

Beyond the aforementioned limitations of sincalide, concerns about inadequate quality control in pharmacy-compounded versions – which could jeopardize diagnosis and physician responsibility – have led to the exploration of alternative methods for assessing GBEF, such as using fatty meals as a cholecystagogue.[3] Fatty meals stimulate the release of endogenous cholecystokinin from enteroendocrine I cells, distributed throughout the crypts and villi of the duodenum and jejunum, through receptor-mediated increases in intracellular calcium signaling.[4] This approach is considered more physiological and better tolerated by patients, making it a prudent alternative to sincalide.[567] Despite its potential, the widespread adoption of fatty meal protocols is hindered by the lack of standardization and the challenge of establishing normative GBEF values across different populations.

Much of the current literature on GBEF using fatty meals comes from studies conducted outside of India,[89] where dietary habits and the composition of fatty meals differ significantly from those in India. The normative data are contingent on the specific type and quantity of fatty meals employed in these studies. The lack of normative data specific to the Indian population has hindered the clinical application of fatty meal-stimulated GBEF assessments in this region. This study was undertaken to bridge this gap. The primary objective was to establish the reference value of GBEF using a fatty meal protocol tailored to the dietary habits of the Indian population. Secondary objectives included evaluating GBEF at various time points and examining variations based on gender and age.

Materials and Methods

Results

A total of 30 consecutive healthy individuals (19 females, 11 males) were initially enrolled in the study. Seven individuals (6 females and 1 male) had no gallbladder emptying at all time points or initial emptying, followed by no emptying with or without gallbladder refilling at later time points. As the possibility of clinically undiagnosed gallbladder dyskinesia or abnormal GBEF secondary to delayed gastric emptying could not be ruled out, these subjects were excluded from the study. A total of 23 consecutive healthy individuals (13 females and 10 males) with a mean age of 42 ± 12 years (median: 39 years; range: 23–62 years) participated in the study. The reference image for maximum gallbladder activity and minimal liver activity was consistently found at 60 min postradiotracer administration, making it the reference premeal image for analysis. The summary statistics of GBEF are summarized in Table 2.

Gender-based variations in gallbladder ejection fraction

No significant differences were observed in GBEF between females and males at any time point (P ≥ 0.770), with equivalent mean and median GBEF values for both genders at 30, 45, and 60 min [Table 3 and Figure 1].

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Figure 1 Box plots comparing the gallbladder ejection fraction between females and males. GBEF: Gallbladder ejection fraction

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Table 3 Comparison of gallbladder ejection fraction between females and males

Parameter	Females		Males		P*
	Mean±SD	Median (range)	Mean±SD	Median (range)
GBEF (%) at 30 min	37±24	43 (3–81)	36±13	33 (21–63)	0.924
GBEF (%) at 45 min	51±27	48 (12–89)	48±20	43 (25–86)	0.770
GBEF (%) at 60 min	56±26	54 (17–91)	54±19	47 (33–87)	0.874

*P value based on independent samples t-test. GBEF: Gallbladder ejection fraction, SD: Standard deviation

Relationship between age and gallbladder ejection fraction

No significant correlation was found between age and GBEF at any of the time points, with Pearson’s correlation coefficients of 0.017, −0.039, and − 0.050 for 30, 45, and 60 min time points, respectively (P ≥ 0.820) [Figure 2].

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Figure 2 Scatter plots between age and gallbladder ejection fraction. GBEF: Gallbladder ejection fraction

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Gallbladder ejection fraction at different time points

At 30 min, the mean GBEF was 36% ± 20%, increasing to 50% ± 23% at 45 min and 55 ± 23% at 60 min. The differences in GBEF across time points were statistically significant (P < 0.0001). Furthermore, on post hoc pairwise comparison with Bonferroni adjustment between each pair of time points, the differences were statistically significant (P < 0.001) [Table 4 and Figure 3]. Most of the gallbladder emptying occurred during the early phase (30–45 min), with continued emptying observed into the later phase (up to 60 min) [Figure 3].

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Figure 3 Box plot (a) and estimated marginal means (b) of gallbladder ejection fraction across different time points. GBEF: Gallbladder ejection fraction

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Table 4 Comparison of gallbladder ejection fraction between different time points

One-way repeated measures ANOVA
GBEF (%), min		Mean±SD		Median (range)	F	P		Partial eta squared
30		36±20		34 (3–81)	46.565	<0.0001		0.679
45		50±23		48 (12–89)
60		55±23		51 (17–91)
Post hoc paired samples t-test
GBEF (30 vs. 45 min)			GBEF (45 vs. 60 min)			GBEF (30 vs. 60 min)
t	P*	Cohen’s d	t	P*	Cohen’s d	t	P*	Cohen’s d
−5.043	<0.001	1.052	−6.129	<0.001	1.278	−6.824	<0.001	1.423

*P value with Bonferroni adjustment for multiple comparisons. GBEF: Gallbladder ejection fraction, SD: Standard deviation

Reference value of gallbladder ejection fraction

The reference value of GBEF was determined by considering the 5^th percentile value at 60 min (assuming that 95% of the healthy population had values greater than or equal to this threshold). The reference cutoff of GBEF was thus established as ≥20% at 60 min after fatty meal ingestion. Figure 4 shows the representative image of the GBEF estimation of a healthy control.

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Figure 4 Gallbladder ejection fraction (GBEF) assessment in a 52-year-old female healthy control. Selection of the gallbladder reference image (a) where the gallbladder is visualized clearly and the liver activity is minimum (arrows) at 60 min. Results of GBEF assessment (b). EF: Ejection fraction

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Discussion

The findings of this study provide important insights into the assessment of gallbladder function using a fatty meal protocol in a healthy Indian cohort. The premeal image showing maximum gallbladder activity with minimal liver activity was consistently identified at 60 min after radiotracer administration. It aligns with previous studies, ensuring optimal gallbladder visualization and minimal liver activity interference.[1011] This consistency across studies highlights the reliability of the 60-min mark as the reference time to acquire the reference premeal image for the GBEF assessment. Furthermore, the use of a standard fatty meal, specifically tailored to the Indian dietary context, addresses a significant gap in the literature. The results indicate that the GBEF values obtained in this study are within the lower range of those reported in the literature, likely due to the differences in the image acquisition and analysis (namely, dynamic versus static), state of the meal (liquid versus solid), and specific nutritional content of the meal used. The variability in GBEF values reported in the literature underscores the importance of standardizing fatty meal protocols for GBEF assessment.[89] The fatty meal used in this study, composed of 40 g of butter and two slices of white bread, was selected due to its easy availability, low cost, reproducibility, palatability, and acceptance within the Indian population.

Notably, this study found no significant gender-based differences in GBEF, contradicting some previous research that suggested higher ejection fractions in females.[12] This discrepancy could be attributed to differences in meals, methodologies, or ethnic variations, underscoring the need for further research in this area. In addition, the lack of significant age correlation with GBEF in this study contrasts with other findings that have suggested age-related declines in gallbladder function.[13] Our study found a very weak, statistically insignificant positive correlation between age and GBEF at 30 min (r = 0.017, P = 0.939), while negative but insignificant correlations were observed at 45 min (r = −0.039, P = 0.860) and 60 min (r = −0.050, P = 0.820). It is important to note that due to the limited sample size, our study lacks sufficient power to draw definitive conclusions regarding gender- and age-related variations in GBEF.

Our study found that GBEF increased at later time points after fatty meal ingestion, with statistically significant differences observed between each pair of time points [Table 4 and Figure 3]. This aligns with Krishnamurthy and Brown’s findings that GBEF is time dependent and varies with extended data acquisition, suggesting the importance of reporting GBEF with a specific time reference.[11] It has been reported that maximum gallbladder emptying typically occurs 40–60 min after ingesting a fatty meal, with the majority of emptying happening in the early phase, followed by slower emptying over time.[37] Our findings, as shown in Table 4 and Figure 3, are consistent with this, revealing that most gallbladder emptying occurs early on. The literature suggests that GBEF measured at 60 min offers the best diagnostic yield, with minimal to no additional benefit from extending the assessment beyond this time.[1271415] Building on this foundation, our study established GBEF at the 60 min time point after fatty meal ingestion.

Our study focused on exploring alternative methods to stimulate gallbladder ejection using fatty meals. Although this approach has been implemented globally for years, there remains a lack of consensus among major professional societies on the standardization of a well-defined meal and its corresponding imaging protocol.[8] The reproducibility of GBEF estimation with fatty meals is well documented, while mixed results have been reported for sincalide cholescintigraphy, with recent studies suggesting that the latter has poor reproducibility.[16171819] In addition, there has been a recent proposal to shorten the duration of sincalide cholescintigraphy for GBEF estimation to 30 min.[20] Our study offers a more patient-friendly approach, involving short static imaging sessions of just 2 min each, rather than the cumbersome 60 min continuous imaging required by the current recommended method. Recent research also supports the use of GBEF estimation with fatty meals as a more affordable and reliable alternative to sincalide cholescintigraphy.[21] These recent findings further validate our approach to GBEF estimation, which utilizes a low-cost, easily accessible, reproducible, palatable, and culturally appropriate fatty meal. This method is especially relevant given the logistical challenges associated with sincalide, such as its limited availability and the stringent quality control requirements for pharmaceutical-grade compounds.

The reference values established in this study for GBEF in a healthy Indian cohort have direct clinical relevance. Specifically, these values may aid in the diagnostic evaluation of functional gallbladder disorders such as chronic acalculous cholecystitis or gallbladder dyskinesia, conditions often characterized by biliary symptoms without gallstones. In such cases, a reduced GBEF is frequently used to support the diagnosis and guide decisions regarding cholecystectomy.[12] By providing normative data specific to the Indian population, this study makes the GBEF assessment more relevant and reliable in local clinical settings, potentially reducing false positives and improving diagnostic confidence.

While the study offers valuable insights, it is important to acknowledge its limitations. The sample size was relatively modest, comprising just 23 participants, which may not fully reflect the variability in GBEF across a more diverse population. This limited sample size also impacts the generalizability of the findings, especially when accounting for demographic factors such as age and gender. Another limitation is the inability to rule out undiagnosed delayed gastric emptying, which may have influenced GBEF, as gastric emptying was not evaluated in the participants. In addition, the findings may not be applicable to children or individuals under 18 years of age, as the study focused solely on adults. Future studies should consider multicenter validation across diverse geographic and dietary populations to strengthen the external validity of the reference GBEF values established here. Furthermore, incorporating dynamic imaging protocols or hybrid approaches that combine both static and dynamic acquisitions may enhance diagnostic accuracy and allow direct comparisons with sincalide-based methods. These enhancements could contribute to standardizing fatty meal-based cholescintigraphy, furthermore, as a reliable alternative in various clinical settings.

Conclusion

This study established the reference GBEF values at 60 min postfatty meal ingestion in a healthy Indian cohort, aligning with existing clinical recommendations. The use of a culturally appropriate, low-cost, and easily reproducible fatty meal offers a practical and patient-friendly alternative to sincalide-based cholescintigraphy. This approach not only reduces imaging time and patient discomfort but also holds significant clinical utility in settings where sincalide is either unavailable, prohibitively expensive, or difficult to quality control. Importantly, it may serve as a valuable triage tool for identifying patients who require further evaluation, thereby improving access to functional gallbladder assessment in resource-limited or real-world clinical environments.