Gastric Emptying Scintigraphy Protocols: An Educational Guide to the Rationale for Standardization

Objectives In 2009, SNMMI published Procedure Guideline for Adult Solid-Meal Gastric-Emptying Study 3.0 with the aim of standardizing the performance of gastric emptying scintigraphy (GES) protocols and avoiding issues of unreliable test results, non-valid clinical interpretations and problematic variations between nuclear medicine sites.1 This guideline reflected the consensus of several professional societies.2 Data obtained from laboratories applying for accreditation from the Intersocietal Accreditation Commission (IAC) show that >6 years after publication of the guidelines, there is a low rate of compliance with the consensus GES protocol, e.g. at 129 sites, compliance with the recommended meal was 31%. Only a minority (13.2%) of protocols were fully compliant with the major consensus protocol elements. This may be due to a lack of knowledge concerning the importance of these factors. The learning objectives of this educational abstract are: - Explain the concepts/rationale underlying important aspects of the GES consensus guidelines -Provide a practical technical guide to creating a standardized protocol Here follows a brief outline of topics. We will illustrate these with case examples and a variety of useful references. Withholding Medications: In general, unless a treatment response is the purpose of the GES study, patients should withhold medications that alter GE for 48-72 hours, depending on drug half-life. While there is an awareness of the effects of prokinetic drugs e.g. metaclopramide, less consideration is given for drugs not specifically prescribed for their gastrointestinal action, e.g opiates, erthyromycin, atropine, theophylline, and benzodiazepines.1 Blood Glucose: Hyperglycemia is an important cause of GE delay. In diabetics, control of fasting hyperglycemia to <275 mg/dL is recommended.2 Composition of the test meal is the major source of variability. GE depends on meal composition (caloric content and volume). Solids, indigestible foods, and fats empty more slowly than liquids, highly digestible foods, proteins or carbohydrates. The liquid egg whites must be cooked together with the sulfur colloid forming a bond to trace true solid GE. It cannot be emphasized more strongly that alternative meals have no validity in establishing GES results unless specific normal databases have been developed. A common error is to simply add tracer to an already prepared solid food, e.g., meat stew. However, the tracer does not remain associated with the solid particles. Another common protocol variant is to use whole eggs rather than the recommended liquid egg product but tracer binding is reduced for the former.3 Incomplete meal ingestion or vomiting can lead to confounding results (apparently more rapid emptying) and must be reported. Imaging intervals and duration -The consensus protocol recommends imaging up to 4 hours for greater sensitivity in detecting delayed GE. The literature has suggested that retention >10% of the meal at 4 hours is abnormal and is the best discriminator between normal and abnormal results.4 New literature suggesting that a shortened protocol may be a satisfactory compromise will be addressed. This issue is complex because of differences in gastric fundal and antral actions. Many labs persist in using half-time of emptying (T1/2) for assessing GE but this should be discouraged as the ideal methodology takes into account the entire curve (non-exponential for solids). This educational abstract will assist technologists and physicians to develop GES protocols that are not only customized for their specific equipment, but are also compliant with the consensus recommendations. Consistent national/international use of the consensus GES protocols

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