13C mixed triglyceride breath test: a noninvasive method to assess lipase activity in children

A standardised nutritional drink as a test meal for the 13 C mixed triglyceride breath test for pancreatic exocrine insufficiency: A randomised, two-arm crossover comparative study

BACKGROUND

The 13 C mixed triglyceride breath test (13 C MTGT) is a diagnostic test for pancreatic exocrine insufficiency (PEI). It is poorly standardised with much heterogeneity of the test meal, the commonest being toast and butter. A standardised oral nutritional supplement that could be easily transported, stored and made up would be valuable for making this test accessible outside of specialist centres.

METHODS

A prospective, randomised, two-arm crossover study of different test meals was carried out in 14 healthy controls. The 13 C MTGT was performed in identical conditions on two separate days. Two test meals were given in random order, either standard (toast and butter) or novel (oral nutritional supplement), with 250 mg of 13 C-labelled mixed triglyceride incorporated. Breath samples were taken postprandially to calculate cumulative percentage dose recovery (cPDR) of 13 C at 6 h.

RESULTS

All 14 participants completed both arms of the study with no protocol deviations. The mean cPDR was 39.39% (standard deviation [SD] 5.19) for the standard test meal and 39.93% (SD 5.20) for the novel test meal. A one-way repeated measures analysis of variance (ANOVA) found no significant difference in cPDR between the two meals, F(1, 13) = 0.18, p = 0.68 (minimum detectable difference of 0.81 at 80% power).

CONCLUSION

This study demonstrates that a standardised oral nutritional supplement can be used without compromising 13 C recovery. Using this test meal provides a standardised dietary stimulus to the pancreas, avoiding possible variation in quantity of dietary components with other test meals. Further, the ease of use of this method would help establish the 13 C MTGT test more widely.

Estimation of exocrine pancreatic insufficiency in children with acute pancreatitis using the 13C mixed triglyceride breath test

BACKGROUND

/Objective: The extent of exocrine pancreatic insufficiency (EPI) in the paediatric population with acute pancreatitis (AP) is unknown. The primary objective was to use a 6 h stable-isotope breath test to determine the prevalence of EPI in children with AP. The secondary objective was to determine the diagnostic ability of a 4 h abbreviated breath test in the detection of EPI.

METHODS

13C-mixed triglyceride (MTG) breath test was used to measure fat digestibility in 12 children with AP and 12 normal children. EPI was diagnosed based on a cumulative dose percentage recovery (cPDR) cut-off value < 26.8% present in literature. To reduce the test burden, the diagnostic accuracy of an abbreviated 4 h test was evaluated, using a cPDR cut-off that was the 2.5th percentile of its distribution in control children.

RESULTS

The cPDR of cases was significantly lower than that of controls (27.71 ± 7.88% vs 36.37 ± 4.70%, p = 0.005). The cPDR during acute illness was not significantly different to that at 1 month follow up (24.69 ± 6.83% vs 26.98 ± 11.10%, p = 0.52). The 4 h and 6 h breath test results correlated strongly (r = 0.93, p < 0.001) with each other. The new 4 h test had 87.5% sensitivity and 93.8% specificity for detecting EPI.

CONCLUSION

Two-thirds (66.7%) of this sample of children with AP had EPI during admission, which persisted at 1 month follow up. The 4 h abbreviated 13C-MTG breath test has good diagnostic ability to detect EPI in children and may improve its clinical utility in this age group.

High prevalence of gastrointestinal symptoms in patients with primary Sjögren's syndrome cannot be attributed to pancreatic exocrine insufficiency

INTRODUCTION

Pancreatic exocrine insufficiency (PEI) results in maldigestion of fat, leading to steatorrhea, malabsorption and weight loss. Sjögren's syndrome (SS) is a chronic autoimmune rheumatic disease with unknown etiology. The exocrine pancreas and the salivary glands are functionally and histologically comparable, and pancreatic dysfunction in SS has been hypothesized.

METHODS

Patients were recruited from the Department for Rheumatology at the Karolinska University Hospital in Stockholm, Sweden, between June and December 2019. PEI was assessed by fecal elastase-1 (FE-1) and ¹³C-mixed triglyceride breath test (¹³C-MTG-BT). The presence and severity of gastrointestinal symptoms were assessed by a well-established and validated survey based on a seven-point Likert scale.

RESULTS

Fifty-seven patients with primary SS were included in the study, comprising 92% females with a median age of 63 years. In total, 87% of SS patients were tested for FE-1 and all had normal results. All patients who underwent a ¹³C-MTG-BT had a normal cumulative ¹³C-exhalation. Compared to the control group, significantly more patients suffered from gastrointestinal (GI) symptoms (p < .01). The same number of patients noted moderate to severe loose bowel movements or constipation (38%). Eleven GI symptom parameters were compared to controls and the highest odd ratios were noted for the following moderate to severe symptoms: bloating, feeling of incompletely emptied bowel after defecation and abdominal pain relieved by bowel action.

CONCLUSION

In our study, most SS patients suffered from irritable bowel syndrome (IBS)-like GI symptoms that could not be attributed to PEI.

Review of paediatric gastrointestinal physiology relevant to the absorption of orally administered medicines

Despite much progress in regulations to improve paediatric drug development, there remains a significant need to develop better medications for children. For the design of oral dosage forms, a detailed understanding of the specific gastrointestinal (GI) conditions in children of different age categories and how they differ from GI conditions in adults is essential. Several review articles have been published addressing the ontogeny of GI characteristics, including luminal conditions in the GI tract of children. However, the data reported in most of these reviews are of limited quality because (1) information was cited from very old publications and sometimes low quality sources, (2) data gaps in the original data were filled with textbook knowledge, (3) data obtained on healthy and sick children were mixed, (4) average data obtained on groups of patients were mixed with data obtained on individual patients, and (5) results obtained using investigative techniques that may have altered the outcome of the respective studies were considered. Consequently, many of these reviews draw conclusions that may be incorrect. The aim of the present review was to provide a comprehensive and updated overview of the available original data on the ontogeny of GI luminal conditions relevant to oral drug absorption in the paediatric population. To this end, the PubMed and Web of Science metadatabases were searched for appropriate studies that examined age-related conditions in the oral cavity, esophagus, stomach, small intestine, and colon. Maturation was observed for several GI parameters, and corresponding data sets were identified for each paediatric age group. However, it also became clear that the ontogeny of several GI traits in the paediatric population is not yet known. The review article provides a robust and valuable data set for the development of paediatric in vitro and in silico biopharmaceutical tools to support the development of age-appropriate dosage forms. In addition, it provides important information on existing data gaps and should provide impetus for further systematic and well-designed in vivo studies on GI physiology in children of specific age groups in order to close existing knowledge gaps and to sustainably improve oral drug therapy in children.

An ESPGHAN Position Paper on the Use of Breath Testing in Paediatric Gastroenterology

OBJECTIVES

Given a lack of a systematic approach to the use of breath testing in paediatric patients, the aim of this position paper is to provide expert guidance regarding the indications for its use and practical considerations to optimise its utility and safety.

METHODS

Nine clinical questions regarding methodology, interpretation, and specific indications of breath testing and treatment of carbohydrate malabsorption were addressed by members of the Gastroenterology Committee (GIC) of the European Society for Paediatric Gastroenterology Hepatology and Nutrition (ESPGHAN).A systematic literature search was performed from 1983 to 2020 using PubMed, the MEDLINE and Cochrane Database of Systematic Reviews. Grading of Recommendations, Assessment, Development, and Evaluation was applied to evaluate the outcomes.During a consensus meeting, all recommendations were discussed and finalised. In the absence of evidence from randomised controlled trials, recommendations reflect the expert opinion of the authors.

RESULTS

A total of 22 recommendations were voted on using the nominal voting technique. At first, recommendations on prerequisites and preparation for as well as on interpretation of breath tests are given. Then, recommendations on the usefulness of H2-lactose breath testing, H2-fructose breath testing as well as of breath tests for other types of carbohydrate malabsorption are provided. Furthermore, breath testing is recommended to diagnose small intestinal bacterial overgrowth (SIBO), to control for success of Helicobacter pylori eradication therapy and to diagnose and monitor therapy of exocrine pancreatic insufficiency, but not to estimate oro-caecal transit time (OCTT) or to diagnose and follow-up on celiac disease.

CONCLUSIONS

Breath tests are frequently used in paediatric gastroenterology mainly assessing carbohydrate malabsorption, but also in the diagnosis of small intestinal overgrowth, fat malabsorption, H. pylori infection as well as for measuring gastrointestinal transit times. Interpretation of the results can be challenging and in addition, pertinent symptoms should be considered to evaluate clinical tolerance.

Assessment of exocrine pancreatic function in children and adolescents with direct and indirect testing

The exocrine pancreas plays an important role in digestion. Understanding of the physiology and regulation of exocrine function provides insight into disease processes and basis of functional testing. Specifically, exocrine pancreatic insufficiency (EPI) can cause maldigestion and thus a proper assessment of exocrine pancreatic function is important. There are indirect and direct methods for evaluating pancreatic function. Indirect methods are varied and include stool, serum, urine, and breath tests. Fecal elastase is a commonly used indirect test today. Direct methods involve stimulated release of pancreatic fluid that is collected from the duodenum and analyzed for enzyme activity. The most used direct test today is the endoscopic pancreatic function test. Indirect pancreatic function testing is limited in identifying cases of mild to moderate EPI, and as such in these cases, direct testing has higher sensitivity and specificity in diagnosing EPI. This review provides a comprehensive guide to indirect and direct pancreatic function tests as well as an in-depth look at exocrine pancreatic function including anatomy, physiology, and regulatory mechanisms.

European guideline on indications, performance and clinical impact of 13 C-breath tests in adult and pediatric patients: An EAGEN, ESNM, and ESPGHAN consensus, supported by EPC

Introduction

¹³C‐breath tests are valuable, noninvasive diagnostic tests that can be widely applied for the assessment of gastroenterological symptoms and diseases. Currently, the potential of these tests is compromised by a lack of standardization regarding performance and interpretation among expert centers.

Methods

This consensus‐based clinical practice guideline defines the clinical indications, performance, and interpretation of ¹³C‐breath tests in adult and pediatric patients. A balance between scientific evidence and clinical experience was achieved by a Delphi consensus that involved 43 experts from 18 European countries. Consensus on individual statements and recommendations was established if ≥ 80% of reviewers agreed and <10% disagreed.

Results

The guideline gives an overview over general methodology of ¹³C‐breath testing and provides recommendations for the use of ¹³C‐breath tests to diagnose Helicobacter pylori infection, measure gastric emptying time, and monitor pancreatic exocrine and liver function in adult and pediatric patients. Other potential applications of ¹³C‐breath testing are summarized briefly. The recommendations specifically detail when and how individual ¹³C‐breath tests should be performed including examples for well‐established test protocols, patient preparation, and reporting of test results.

Conclusion

This clinical practice guideline should improve pan‐European harmonization of diagnostic approaches to symptoms and disorders, which are very common in specialist and primary care gastroenterology practice, both in adult and pediatric patients. In addition, this guideline identifies areas of future clinical research involving the use of ¹³C‐breath tests.

13 C Breath Tests in Infections and Beyond

Stable isotope labeled compounds are widely used as diagnostic probes in medicine. These diagnostic stable isotope probes are now being expanded in their scope, to provide precise indications of the presence or absence of etiologically significant change in metabolism due to a specific disease. This concept exploits a labeled tracer probe that is a specifically designed substrate of a “gateway” enzyme in a discrete metabolic pathway, whose turnover can be measured by monitoring unidirectional precursor product mass flow. An example of such a probe is the 13C-urea breath test, where labeled urea is given to patients with H. pylori infection. Another example of this kind of probe is used to study the tripeptide glutathione (glu-cys-gly, GSH), which is the most abundant cellular thiol, and protects cells from the toxic effects of reactive oxygen species. Within the gamma glutamyl cycle, 5-oxoproline (L-pyroglutamic acid) is a metabolite generated during GSH catabolism, and is metabolized to glutamic acid by 5-oxoprolinase. This enzyme can also utilize the substrate L-2-oxothiazolidone-4-carboxylate (OTC), to generate intracellular cysteine, which is beneficial to the cell. Thus, labeled (13C) OTC would, under enzymatic attack yield cysteine and 13CO2, and can thus track the state and capacity of glutathione metabolism. Similarly, stable isotope labeled probes can be used to track the activity of the rate of homocysteine clearance, lymphocyte CD26, and liver CYP (cytochrome P450) enzyme activity. In the future, these applications should be able to titrate, in vivo, the characteristics of various specific enzyme systems in the body and their response to stress or infection as well as to treatment regimes.

13C-Mixed Triglyceride Breath Test and Fecal Elastase as an Indirect Pancreatic Function Test in Cystic Fibrosis Infants

BACKGROUND

The 'gold standard' test for the indirect determination of pancreatic function status in infants with cystic fibrosis (CF), the 72-hour fecal fat excretion test, is likely to become obsolete in the near future. Alternative indirect pancreatic function tests with sufficient sensitivity and specificity to determine pancreatic phenotype need further evaluation in CF infants.

OBJECTIVE

Evaluation of the clinical utility of both the noninvasive, nonradioactive C-mixed triglyceride (MTG) breath test and fecal elastase-1 (FE1) in comparison with the 72-hour fecal fat assessment in infants with CF.

METHODS

C-MTG breath test and the monoclonal and polyclonal FE1 assessment in stool was compared with the 72-hour fecal fat assessment in 24 infants with CF. Oral pancreatic enzyme substitution (PERT; if already commenced) was stopped before the tests.

RESULTS

Sensitivity rates between 82% and 100% for CF patients with pancreatic insufficiency assessed by both the C-MTG breath test and the FE1 tests proved to be high and promising. The C-MTG breath test (31%-38%) as well as both FE1 tests assessed by the monoclonal (46%-54%) and the polyclonal (45%) ELISA kits, however, showed unacceptably low-sensitivity rates for the detection of pancreatic-sufficient CF patients in the present study.

CONCLUSIONS

The C-MTG breath test with nondispersive infrared spectroscopy (NDIRS) technique, as well as both FE1 tests, are not alternatives to the fecal fat balance test for the evaluation of pancreatic function in CF infants during the first year of life.

Chronic Pancreatitis: Current Status and Challenges for Prevention and Treatment

This paper reviews the current status of our understanding of the epidemiology, diagnosis, and management of the continuum of pancreatic diseases from acute and recurrent acute pancreatitis to chronic pancreatitis and the diseases that are often linked with pancreatitis including diabetes mellitus and pancreatic cancer. In addition to reviewing the current state of the field, we identify gaps in knowledge that are necessary to address to improve patient outcomes in these conditions.

Preliminary report of the (13)C-mixed triglyceride breath test to assess timing of pancreatic enzyme replacement therapy in children with cystic fibrosis

BACKGROUND

Despite guidelines suggesting pancreatic enzyme replacement therapy (PERT) should be taken before or during a meal, it is currently unknown whether this has benefits over administration after a meal in individuals with cystic fibrosis (CF).

METHODS

18 children with pancreatic insufficient CF were randomised to two (13)C-mixed triglyceride ((13)C-MTG) breath tests to assess lipase activity with PERT administered 10min before and 10min after a meal. Results were expressed as percentage cumulative dose recovered (PCDR) of (13)CO2 and were compared with established values in healthy subjects. Gastric half emptying time (T½) was also assessed by a (13)C-octanoate breath test.

RESULTS

There was no difference in mean PCDR of (13)CO2 between taking PERT before versus after the meal (p=0.68). Eleven subjects had a greater PCDR when PERT was taken before and 7 when PERT was taken after the meal. 6/8 subjects (75%) with a lower than normal PCDR at one time point normalised PCDR when PERT timing was changed. When PERT was taken after the meal, PCDR was higher in normal vs. fast T½ (p=0.04).

CONCLUSIONS

Changing PERT timing can result in normalised lipase activity. Gastric emptying rate may influence optimal timing of PERT. Clinical Trial Registration Number - This study was undertaken prior to the registration process being a commonly required practice.

Assessment of intestinal malabsorption

Significant efforts have been made in the last decade to either standardize the available tests for intestinal malabsorption or to develop new, more simple and reliable techniques. The quest is still on and, unfortunately, clinical practice has not dramatically changed. The investigation of intestinal malabsorption is directed by the patient's history and baseline tests. Endoscopy and small bowel biopsies play a major role although non-invasive tests are favored and often performed early on the diagnostic algorithm, especially in paediatric and fragile elderly patients. The current clinically available methods and research tools are summarized in this review article.

(13)C mixed triglyceride breath testing using infrared spectrometry: comparison of two devices in early infancy

BACKGROUND/OBJECTIVES

The (13)C mixed triglyceride (MTG) breath test has been proposed for the non-invasive assessment of fat digestion and absorption. To evaluate whether reference values for the adequacy of fat absorption, set in the non-dispersive infrared spectrometry (NDIRS) system software proposed for healthy children and adults using the (13)C MTG breath test, are also applicable to infants of <5 months of age.

SUBJECTS/METHODS

(13)C MTG breath testing with the NDIRS technique was performed in 54 healthy infants <5 months of age (38 breast-fed, 16 formula-fed) and six infants diagnosed with cystic fibrosis (CF) using two NDIRS devices, IRIS and FANci2.

RESULTS

The IRIS results were slightly higher compared with those assessed by the FANci2 device. The minimum cutoff value for pancreatic sufficiency (PS) is set as a cumulative percentage dose of (13)C recovered (cPDR) after 5 h of 13.0%. Pancreatic function status of six CF infants, three with PS and three with pancreatic insufficiency (PI), according to the 72 h-faecal fat balance test could be correctly determined with the (13)C MTG breath test using two NDIRS techniques. However, if these reference values had been used to determine pancreatic function status in healthy infants, 26 out of 54 infants would have been misclassified as pancreatic insufficient.

CONCLUSIONS

Although the (13)C MTG breath test with the MS technique has the potential to be a suitable assessment of fat absorption in infants, the technique of NDIRS appears too insensitive in an infant population group.

ESPGHAN and NASPGHAN Report on the Assessment of Exocrine Pancreatic Function and Pancreatitis in Children

The purpose of this clinical report is to discuss several recent advances in assessing exocrine pancreatic insufficiency (EPI) and pancreatitis in children, to review the array of pancreatic function tests, to provide an update on the inherited causes of EPI, with special emphasis on newly available genetic testing, and to review newer methods for evaluating pancreatitis.

Malabsorption blood test: Assessing fat absorption in patients with cystic fibrosis and pancreatic insufficiency

The malabsorption blood test (MBT), consisting of pentadecanoic acid (PA), a free fatty acid, and triheptadecanoic acid (THA), a triglyceride that requires pancreatic lipase for absorption of the heptadecanoic acid (HA), was developed to assess fat malabsorption in patients with cystic fibrosis (CF) and pancreatic insufficiency (PI). The objective was to construct a population pharmacokinetic (PK) model to describe PA and HA disposition in healthy subjects and CF subjects. A model was simultaneously fit to PA and HA concentrations, consisting of 1-compartment disposition and a transit model to describe absorption. PA bioavailability estimates for CF subjects without pancreatic enzyme administration (1.07 [0.827, 1.42]) and with enzymes (0.88 [0.72, 1.09]) indicated PA absorption comparable to healthy subjects. HA bioavailability in CF without enzyme administration was 0.0292 (0.0192, 0.0459) and with enzymes increased to 0.606 (0.482, 0.823). In CF, compared with taking enzymes with the MBT, HA bioavailability was further decreased by factors of 0.829 (0.664, 0.979) and 0.78 (0.491, 1.13) with enzymes taken 30 and 60 minutes after MBT, respectively. The MBT detected differences in fat absorption in subjects with CF with and without enzyme administration and with changes in enzyme timing. Future studies will address application of the MBT in CF and other malabsorption diagnoses.

Treatment of infants and toddlers with cystic fibrosis-related pancreatic insufficiency and fat malabsorption with pancrelipase MT

BACKGROUND

Pancreatic enzyme replacement therapy (PERT) improves nutritional status and growth in patients with cystic fibrosis (CF) with pancreatic insufficiency (PI). The current recommendation for infants and young children, who are not able to swallow the whole capsule, is to open the capsule and mix the beads in a spoon with some applesauce; however, the efficacy and safety data of this approach are currently lacking. The aim of this study was to assess the efficacy, palatability (ease of swallowing), and safety of 4 dose levels of pancrelipase microtablets (Pancrease MT) in infants and young children with CF-related PI.

PATIENTS AND METHODS

This study was a phase II randomized, investigator-blinded, parallel-group pilot study in DNA-proven infants with CF and PI. The study design included a run-in period (days 1-5) and an experimental period (days 6-11). Pancrelipase microtablets (2-mm, enteric coated) were provided orally. Sixteen subjects, 6 to 30 months of age, were provided 500 U lipase/kg/meal for 5 days (baseline period). Subsequently, subjects were randomly assigned to 1 of 4 treatment groups (each n = 4), receiving 500, 1000, 1500, or 2000 U (Ph. EUR) of lipase/kg/meal, respectively, for 5 days (experimental period). The primary endpoint was medication efficacy assessed by the 72-hour fecal fat excretion, expressed as coefficient of fecal fat absorption (CFA), and 13C mixed triglyceride breath test. Secondary endpoints were safety and palatability.

RESULTS

Overall compliance, defined as used study medication, was 89% to 99% for the entire study. None of the 4 dose regimens significantly influenced the CFA, relative to the baseline period (median range 83%-93%). During the run-in period the median cumulative % 13C was 11 (range -8 to 59). After randomization the median cumulative % 13C was 18 (range 14-23) in the 500-U, 14 (range -1 to 17) in the 1000-U, 10 (range 10-27) in the 1500-U, and 3 (range 1-49) in the 2000-U groups. Palatability was scored fair to good by the parents in each of the treatment groups. Gastrointestinal symptoms were reported in some patients, including common adverse events reported in clinical trials involving pancreatic enzyme therapy. No serious or other adverse events were reported.

CONCLUSION

Treatment with Pancrease MT at a dosage of 500 U lipase/kg/meal resulted in a CFA of approximately 89% in pediatric subjects ages 6 to 30 months with PI resulting from CF. Pancrease MT doses were well tolerated and mean palatability was scored as fair to good. Present results do not indicate that a dosage higher than 500 U (Ph. EUR) lipase/kg/meal increases the coefficient of fat absorption in a cohort of infants 6 to 30 months of age.

On a refinement of the ¹³C-mixed TAG breath test

The present study was aimed to improve and simplify the 13C-mixed TAG (13C-MTG) breath test while keeping it acceptable for the patient. Healthy volunteers (ten women and eight men) were examined on four occasions, receiving in a random order 300 mg 13C-MTG: (1) contained in two wafers; (2) administered with a 50 g wheat roll; as well as given with either (3) 10 or (4) 30 g butter, spread onto a 50 g wheat roll, as the test meal, respectively. Samples of expiratory air were taken for 6 h postprandially for the mass spectroscopic measurement of 13CO2 enrichment. After intake of the sole 13C-MTG, the cumulative 13C recovery in breath air (AUC) appeared to be unsatisfactory, as after 6 h it did not exceed 10 %. Application of the substrate with the 50 g wheat roll did not bring about any improvement in this parameter. The addition of the unlabelled fat to the test meal dramatically increased the cumulative 13C recovery. However, we found higher values for the momentary 13C recovery and AUC with 10 g butter compared with 30 g. It can be concluded that: (1) addition of unlabelled fat is indispensable to obtain a proper course of the breath 13C elimination during the conduct of the 13C-MTG breath test and (2) it is possible to apply a considerably smaller amount of the unlabelled fat than has previously been recommended for this test.

(13)C breath tests for the assessment of exocrine pancreatic function

The secretin-pancreozymin test is regarded as the most accurate of the pancreatic exocrine function tests but is cumbersome, time consuming, and invasive because it requires duodenal intubation and hormonal stimulation of the pancreas. Fecal analysis of fat, fecal elastase, or chymotrypsin are more practicable but far less sensitive to detect early stages of pancreatic exocrine insufficiency. Several (13)C-labeled substrates that are digested by pancreatic enzymes have been proposed for breath tests, thus assessing the intraluminal activity of pancreatic enzymes and therewith the pancreatic exocrine function. Particularly in pediatrics, (13)C breath tests are suited not only for diagnosis of pancreatic exocrine disorder, but also for therapy control under pancreatic enzyme substitution. However, the costs of substrates, the high time expenditure, and the lack of standardization still limit the clinical use of these breath tests. This review aims to place into perspective the traditional pancreatic exocrine function tests and the newer (13)C breath tests.

Estimation of postoperative fat absorption using the 13C mixed-triglyceride breath test in children with choledochal cyst

No previous studies have focused on postoperative fat malabsorption in children with choledochal cyst (CC) who undergo cyst excision and Roux-en-Y (RY) hepatico-jejunostomy (HJ), a combination of procedures that can lead to the non-physiological mixture of food and bile juice. To examine the effect of RYHJ with cholecystectomy on the fat absorption ability of children with CC, we estimated postoperative fat-absorption ability using the carbon 13-labeled mixed triglyceride (13C-MTG) breath test. Twelve postoperative children with CC and 12 normal control children were administered 13C-MTG orally and asked to give breath samples at six time points: once before the 13C-MTG ingestion and at five 60-min intervals postingestion. Fecal chymotrypsin activity and fecal fat excretion were also measured. The delta value of breath 13CO2 at 3, 4, and 5 h after administration and the 5-h cumulative breath 13CO2 were significantly lower in the CC children than in the controls. There were no significant differences in the fecal chymotrypsin activity or fecal fat excretion of the two groups. Conclusion. Occult fat malabsorption occurs in patients with CC after RYHJ, even in the absence of clinical symptoms or abnormal laboratory data.

13C-breath tests: current state of the art and future directions

13C-breath tests provide a non-invasive diagnostic method with high patient acceptance. In vivo, human and also bacterial enzyme activities, organ functions and transport processes can be assessed semiquantitatively using breath tests. As the samples can directly be analysed using non-dispersive isotope selective infrared spectrometers or sent to analytical centres by normal mail breath tests can be easily performed also in primary care settings. The 13C-urea breath test which detects a Helicobacter pylori infection of the stomach is the most prominent application of stable isotopes. Determination of gastric emptying using test meals labelled with 13C-octanoic or 13C-acetic acid provide reliable results compared to scintigraphy. The clinical use of 13C-breath tests for the diagnosis of exocrine pancreatic insufficiency is still limited due to expensive substrates and long test periods with many samples. However, the quantification of liver function using hepatically metabolised 13C-substrates is clinically helpful in special indications. The stable isotope technique presents an elegant, non-invasive diagnostic tool promising further options of clinical applications. This review is aimed at providing an overview on the relevant clinical applications of 13C-breath tests.

Acetate correction for postabsorption metabolism does not improve the [13C]mixed triacylglycerol breath test

OBJECTIVE

The [C]mixed triacylglycerol (MTG) breath test is a noninvasive measure of fat digestion. After absorption and oxidation, C appears in breath CO2. Recovery is no more than 50% in healthy subjects because of sequestration of acetate in intermediary metabolism. The aims of this study were to investigate interindividual variation and postabsorptive metabolism of MTG using oral [1-C]acetate and to examine the use of correction factors to account for the "missing" label.

PATIENTS AND METHODS

[C]mixed triacylglycerol and [1-C]acetate breath tests were performed on 8 healthy adults, 9 healthy children and 3 children with cystic fibrosis. Breath was sampled for 6 hours on each occasion. The enrichment of CO2 in breath was measured by isotope ratio mass spectrometry. Cumulative percentage dose recovered CO2 during the MTG test was corrected for label absorbed, but not completely oxidized using the cumulative percentage dose recovered during the acetate test.

RESULTS

Mean recovery of C during the [C]MTG test with an acetate correction was close to 100% in healthy subjects: 103.1% (SD, 11.6%) in adults and 98.9% (SD, 30.3%) in children, but the wide variance indicated that some of the assumptions governing the use of acetate corrections with oral tracers may not be valid.

CONCLUSION

The need to perform 2 tests, variation in physical activity between tests and differences in intermediary metabolism preclude the use of acetate correction factors when using [C]MTG to assess intraluminal fat digestion, especially in children.

Improving the specificity of the [13C]mixed triacylglycerol breath test by estimating carbon dioxide production from heart rate

BACKGROUND

The [13C]mixed triacylglycerol (MTG) breath test is a non-invasive measure of fat digestion and can be used to assess the need for enzyme replacement therapy in children with cystic fibrosis (CF). However, it lacks specificity. Quantitation of cumulative percent dose recovered (cPDR) requires knowledge of carbon dioxide production rate (VCO2). A resting value is assumed, but children are unlikely to remain at rest during the test.

OBJECTIVE

To improve the specificity and therefore the positive predictive value (PPV) of the MTG breath test using calibrated heart rate monitors to estimate non-resting VCO2.

DESIGN

Proof of concept study.

SUBJECTS

Six children with CF, 10 healthy children and eight healthy adults performed [13C]MTG breath tests.

METHODS

Heart rate monitors were worn throughout the test. Non-resting VCO2 was estimated continuously from heart rate. Percentage dose recovered was calculated using predicted resting VCO2, measured resting VCO2 and non-resting VCO2 estimated from heart rate. Physical activity level (PAL) was taken as cPDR calculated using non-resting VCO2 divided by cPDR calculated using measured resting VCO2. The cutoff point was determined using two graph-receiver operator characteristics.

RESULTS

Use of calibrated heart rate monitors to estimate non-resting VCO2 improved the specificity of the test. The PPV increased from 0.67 to 0.99. PAL was 1.3 in adults and children who performed the test in hospital, and 1.7 in children who performed the test at home.

CONCLUSION

Individually calibrated heart rate monitors are useful tools to estimate non-resting VCO2 during the [13C]MTG breath test.

Advantages of deuterium-labelled mixed triacylglycerol in studies of intraluminal fat digestion

The (13)C-mixed triacylglcerol (MTG, 1,3-distearyl, 2-[1-(13)C]octanoyl glycerol) breath test is a non-invasive measure of intraluminal fat digestion. Recovery of (13)C in breath CO(2) is incomplete (<50%) owing to sequestration of (13)C into organic molecules via the tricarboxylic acid (TCA) cycle. In addition lack of knowledge of CO(2) production rate (VCO(2)) during the test leads to errors in the calculated percentage dose recovered (PDR). (2)H sequestration into organic molecules is low ( approximately 4%) and is not influenced by factors that affect VCO(2) such as food intake or physical activity. After oxidation of (2)H-labelled macromolecules, the label appears in body water, which can be sampled non-invasively in urine or saliva. After an overnight fast, two healthy adults consumed [(2)H]MTG (1,3-distearyl, 2-[(2)H(15)]octanoyl glycerol) and [(13)C]MTG (1,3 distearyl, 2-[1-(13)C]octanoyl glycerol) simultaneously. Total body water (TBW) was measured by (18)O dilution and also estimated from height and weight. Urine and saliva were sampled at baseline and for 10 h after consumption of the test meal. The abundance of (2)HOH and H(2) (18)O in urine and saliva was measured by continuous-flow isotope-ratio mass spectrometry. Cumulative PDR of (2)H and (18)O was calculated from the plateau enrichment, which was reached by 6 h in both saliva and urine. Recovery of (2)H calculated using measured TBW was compared with that using an estimated value of TBW. Mean recovery of (2)H in saliva was 99.3% and in urine was 96.4%. Errors introduced by estimating TBW were <5%. [(2)H]MTG could provide a simpler, more robust, indirect test of intraluminal fat digestion compared with the (13)C-breath test. Further studies are required in pancreatic insufficient patients.

Rapid identification of dihydropyrimidine dehydrogenase deficiency by using a novel 2-13C-uracil breath test

PURPOSE

Dihydropyrimidine dehydrogenase (DPD)-deficient cancer patients have been shown to develop severe toxicity after administration of 5-fluorouracil. Routine determination of DPD activity is limited by time-consuming and labor-intensive methods. The purpose of this study was to develop a simple and rapid 2-(13)C-uracil breath test, which could be applied in most clinical settings to detect DPD-deficient cancer patients.

EXPERIMENTAL DESIGN

Fifty-eight individuals (50 "normal," 7 partially, and 1 profoundly DPD-deficient) ingested an aqueous solution of 2-(13)C-uracil (6 mg/kg). (13)CO(2) levels were determined in exhaled breath at various time intervals up to 180 min using IR spectroscopy (UBiT-IR(300)). DPD enzyme activity and DPYD genotype were determined by radioassay and denaturing high-performance liquid chromatography, respectively.

RESULTS

The mean (+/-SE) C(max), T(max), delta over baseline values at 50 min (DOB(50)) and cumulative percentage of (13)C dose recovered (PDR) for normal, partially, and profoundly DPD-deficient individuals were 186.4 +/- 3.9, 117.1 +/- 9.8, and 3.6 DOB; 52 +/- 2, 100 +/- 18.4, and 120 min; 174.1 +/- 4.6, 89.6 +/- 11.6, and 0.9 DOB(50); and 53.8 +/- 1.0, 36.9 +/- 2.4, and <1 PDR, respectively. The differences between the normal and DPD-deficient individuals were highly significant (all Ps <0.001).

CONCLUSIONS

We demonstrated statistically significant differences in the 2-(13)C-uracil breath test indices (C(max), T(max), DOB(50), and PDR) among healthy and DPD-deficient individuals. These data suggest that a single time-point determination (50 min) could rapidly identify DPD-deficient individuals with a less costly and time-consuming method that is applicable for most hospitals or physicians' offices.

Splanchnic bed metabolism of glucose in preterm neonates

BACKGROUND

Glucose is a major oxidative substrate for intestinal energy generation in neonatal animals; however, few data in preterm infants are available. Early administration of enteral nutrition, including glucose, may be an effective strategy to support intestinal adaptation to extrauterine life in preterm neonates.

OBJECTIVE

The purpose of the present study was to quantify the first-pass uptake and oxidation of glucose by the splanchnic tissues (intestine and liver) in human neonates.

DESIGN

Eight preterm infants [birth weight ( +/- SD): 1.19 +/- 0.22 kg, gestational age: 29 +/- 1 wk] were studied while they received 2 different enteral intakes (A: 40% enteral, 60% parenteral, total glucose intake = 7.5 +/- 0.5 mg. kg(-1). min(-1), and B: 100% enteral, total glucose intake = 7.8 +/- 0.4 mg. kg(-1). min(-1)). Splanchnic and whole-body glucose kinetics were measured by use of dual-tracer techniques.

RESULTS

During both feeding periods, approximately one-third of dietary glucose intake was utilized during the first pass by the splanchnic tissues. More than three-quarters of this utilized glucose was oxidized in both periods (79 +/- 36% with A and 84 +/- 45% with B). Whole-body glucose oxidation was substantial under both circumstances: 72 +/- 5% and 77% +/- 6% of the glucose flux was oxidized during partial (A) and full (B) enteral feeding, respectively.

CONCLUSIONS

Approximately one-third of dietary glucose is utilized during the first pass by the splanchnic tissues, irrespective of the dietary intake. Most of the utilized glucose is used for energy generation.

Measuring gastric emptying of semisolids in children using the 13C-acetate breath test: a validation study

BACKGROUND AND AIM

Radioscintigraphy is the gold standard for evaluation of gastric emptying in children, but requires exposure to ionising radiation. Therefore, the aim of the study was to validate the non-radioactive 13C-acetate breath test in children in comparison to radioscintigraphy as reference method.

PATIENTS

Twenty-nine children with dyspeptic or respiratory symptoms were tested for gastric emptying disorders simultaneously performing the 13C-acetate breath test and radioscintigraphy.

METHODS

A semisolid oatmeal was doubly labelled with 150 mg 13C-acetate and 50 MBq 99mTechnetium. Breath samples were collected every 5-10 min for 4 h. After mass spectrometrical 13C-analysis, curve fitting of the 13C-cumulative recovery to the modified power exponential function Y = m(1 - e(-kt) calculated the half emptying times of the breath test (t 1/2 (breath)). Scintigraphic image acquisition began immediately after the ingestion of the 99mTechnetium-labelled testmeal at a rate of one frame every 60 s for 1 h.

RESULTS

Six children showed delayed gastric emptying in scintigraphy (t 1/2(scinti) > 60 min). All these children had prolonged half emptying times t 1/2 (breath) in the 13C-acetate breath test. Using a cut-off t 1/2(breath) > 90 min, the 13C-acetate breath test had a sensitivity of 100% and a specificity of 85%. Scintigraphic and breath test half emptying times were linearly correlated (Y = 0.80x + 47.68, r = 0.76, P < 0.00001).

CONCLUSIONS

The 13C-acetate breath test proves to be a reliable, non-radioactive alternative for measuring gastric emptying in children.

Validation of the direct nasopharyngeal sampling method for collection of expired air in preterm neonates

In clinical studies, the oxidation of 13C-labeled substrates to 13CO2 and the measurement of the appearance of excess 13CO2 in expiratory air has progressed to an increasingly common method as it is noninvasive and lacks the radiation exposure associated with the use of 14C. The collection of respiratory CO2 currently used occurs via trapping of CO2 in sodium hydroxide (trapping method), sometimes in conjunction with indirect calorimetry. The aim of the present study was to determine the accuracy of our direct nasopharyngeal sampling method for the collection of breath samples in preterm infants compared with the currently used trapping method. We present a method that simplifies the collection of breath samples in preterm infants. Seven preterm infants with a gestational age of 26-29 wk were studied on different postnatal days (range, 8-52 d) while receiving full enteral feeding. A primed constant 3-h intragastric infusion of [13C]bicarbonate was given, and breath samples were collected by means of direct nasopharyngeal sampling and by a sodium hydroxide trap simultaneously. Breath CO2 isotopic enrichments rose rapidly to reach a plateau by 120 min with <5% variation of plateau in both methods. 13CO2 breath isotopic enrichments obtained by the direct nasopharyngeal sampling method correlated highly (r2 = 0.933; p < 0.0001) with the trapping method. The Bland-Altman analysis showed no significant variability between the two methods and demonstrated that the 95% confidence interval is within +/- 4.68 delta per thousand. These findings validate the simple method of direct nasopharyngeal sampling of expired air in neonates.

Methods for measuring lipid metabolism in vivo

PURPOSE OF REVIEW

This review discusses diverse methods that have been used in several recent papers for the qualitative and quantitative analysis of lipids, studies of lipid oxidation, lipoprotein fractionation, and studies of lipid metabolism and metabolic kinetics using tracers. Papers for this review were selected on the basis of their timeliness, novelty, and/or their potential impact on diverse fields of lipid metabolism.

RECENT FINDINGS

Many methods used for studies of lipid metabolism employ advanced chromatographic and mass spectrometric techniques to characterize lipids. In particular, the use of stable isotopically labeled tracers has become increasingly important to study metabolic kinetics.

SUMMARY

Such developments in methodology will continue to advance studies of lipid metabolism in many areas of clinical interest, including heart disease, obesity, and diabetes.