13Carbon mixed triglyceride breath test and pancreatic enzyme supplementation in cystic fibrosis

Diagnosis and Management of Gastrointestinal Manifestations in Children with Cystic Fibrosis

Cystic fibrosis (CF) is primarily known for its pulmonary consequences, which are extensively explored in the existing literature. However, it is noteworthy that individuals with CF commonly display gastrointestinal (G-I) manifestations due to the substantial presence of the cystic fibrosis transmembrane conductance regulator (CFTR) protein in the intestinal tract. Recognized as pivotal nonpulmonary aspects of CF, G-I manifestations exhibit a diverse spectrum. Identifying and effectively managing these manifestations are crucial for sustaining health and influencing the overall quality of life for CF patients. This review aims to synthesize existing knowledge, providing a comprehensive overview of the G-I manifestations associated with CF. Each specific G-I manifestation, along with the diagnostic methodologies and therapeutic approaches, is delineated, encompassing the impact of innovative treatments targeting the fundamental effects of CF on the G-I tract. The findings underscore the imperative for prompt diagnosis and meticulous management of G-I manifestations, necessitating a multidisciplinary team approach for optimal care and enhancement of the quality of life for affected individuals. In conclusion, the authors emphasize the urgency for further clinical studies to establish a more robust evidence base for managing G-I symptoms within the context of this chronic disease. Such endeavors are deemed essential for advancing understanding and refining the clinical care of CF patients with G-I manifestations.

Coefficient of Fat Absorption to Measure the Efficacy of Pancreatic Enzyme Replacement Therapy in People With Cystic Fibrosis: Gold Standard or Coal Standard?

OBJECTIVES

We sought data on the validity, reliability, responsiveness, and feasibility of the coefficient of fat absorption (CFA) as a measure of pancreatic enzyme replacement therapy (PERT) efficacy in people with cystic fibrosis (pwCF) and reviewed the literature for alternative measures.

METHODS

We searched PubMed for the Medical Subject Heading cystic fibrosis and the key words cystic fibrosis, fat absorption, CFA, and fecal fat imbalance; historical articles; and citations in bibliographies.

RESULTS

The lower the CFA, the greater its variability; thus, it is less variable in healthy individuals who have higher CFA than pwCF. In addition, the test-retest values for CFA are more variable in pwCF than the general population. There is no correlation between CFA and body mass index or PERT dose but CFA is related to gastrointestinal signs and symptoms. Research-quality CFA studies are expensive, time consuming, and odious to pwCF and research staff. Sparse stool tests, breath tests, and blood tests of fat absorption have been studied as potential alternatives to CFA to measure PERT efficacy.

CONCLUSIONS

Based on the evidence, we conclude that CFA as a measure of the efficacy of PERT is more of a "coal standard" than a gold standard; developing suitable alternatives should be a priority.

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.

Bulk and Compound Specific Analysis of Stool Lipid Confirm that the “Missing” 13C in the Mixed Triacylglycerol Breath Test is not in the Stool

The 13C-mixed triacylglycerol (MTG) breath test is used to measure intraluminal fat digestion. In normal digestion 20% to 40% of the ingested 13C label is recovered in breath CO2. We aimed to identify the proportions of ingested label excreted in stool as well as breath following ingestion of 13C-MTG by children with impaired exocrine pancreatic function and healthy controls. 13C enrichment of breath samples was measured by continuous flow isotope ratio mass spectrometry (IRMS) and the cumulative percent dose recovered (cPDR) in 10 hours was calculated. Total 13C of a fecal fat extract from each stool was measured by combustion-IRMS, and 13C enrichment and concentration of the tert.-butyldimethylsilyl (TBDMS) derivative of octanoic acid was measured by gas chromatography-mass spectrometry (GC/MS) after hydrolysis of the fat extract. Stool 5-day cPDR was calculated. Mean breath cPDR was 33% for children with cystic fibrosis and 45% for controls. Mean cPDR in stool by combustion-IRMS and GC/MS, respectively, was 0.7% and 0.3% for children with cystic fibrosis and 1.4 and 4.2% for controls.

Metabolic markers of protein maldigestion after a 15N test meal in minipigs with pancreatic exocrine insufficiency

The effect of pancreatic exocrine insufficiency (PEI) on protein malabsorption is little documented, partly due to methodological barriers. We aimed to validate biomarkers of protein malabsorption using a ¹⁵N test meal in a minipig model of PEI. Six pancreatic duct-ligated minipigs were used as a model of PEI and four nonoperated animals as a control. All animals were equipped with an ileocecal reentrant cannula. Minipigs were given a test meal containing [¹⁵N]casein. The PEI animals repeated the test three times, in the absence of any pancreatic enzymes, or after pancreatic substitution at two levels [ A or B: 7,500 or 75,000 (lipase) and 388 or 3881 (protease) FIP U]. Ileal chyme, urine, and blood were collected postprandially. Nitrogen and ¹⁵N were measured in digestive and metabolic pools. We obtained a gradient of ileal protein digestibility from 29 ± 11% in PEI to 89 ± 6% in the controls and a dose- dependent response of enzymes. Insulin and gastric inhibitory polypeptide secretions were decreased by PEI, an effect that was counteracted with the enzymes at level B. The total recovery of ¹⁵N in urinary urea and plasma proteins was 14 ± 5.1% in the control group and decreased to 5.5 ± 2.1% by PEI. It was dose dependently restored by the treatment. Both ¹⁵N recovery in plasma and urine were correlated to protein digestibility. We confirm that the ¹⁵N transfer in those pools is a sensitive marker of protein malabsorption. Nevertheless, an optimization of the test meal conditions would be necessary in the view of implementing a clinical test. NEW & NOTEWORTHY We designed an intervention study to create a gradient of ileal protein digestibility in minipigs with pancreatic exocrine insufficiency and to validate reliable metabolic markers using a ¹⁵N oral meal test. ¹⁵N recovery in plasma proteins and to a higher extent in urine was sensitive to protein malabsorption. This test is minimally invasive and could be used to reveal protein malabsorption in patients.

Stable Isotope Techniques for the Assessment of Host and Microbiota Response During Gastrointestinal Dysfunction

The International Atomic Energy Agency convened a technical meeting on environmental enteric dysfunction (EED) in Vienna (October 28-30, 2015; https://nucleus.iaea.org/HHW/Nutrition/EED_Technical_Meeting/index.html) to bring together international experts in the fields of EED, nutrition, and stable isotope technologies. Advances in stable isotope-labeling techniques open up new possibilities to improve our understanding of gastrointestinal dysfunction and the role of the microbiota in host health. In the context of EED, little is known about the role gut dysfunction may play in macro- and micronutrient bioavailability and requirements and what the consequences may be for nutritional status and linear growth. Stable isotope labeling techniques have been used to assess intestinal mucosal injury and barrier function, carbohydrate digestion and fermentation, protein-derived amino acid bioavailability and requirements, micronutrient bioavailability and to track microbe-microbe and microbe-host interactions at the single cell level. The noninvasive nature of stable isotope technologies potentially allow for low-hazard, field-deployable tests of gut dysfunction that are applicable across all age groups. The purpose of this review is to assess the state-of-the-art use of stable isotope technologies and to provide a perspective on where these technologies can be exploited to further our understanding of gut dysfunction in EED.

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.

Study design considerations for evaluating the efficacy and safety of pancreatic enzyme replacement therapy in patients with cystic fibrosis

In 2006, the US FDA issued a 'Guidance for Industry' regarding submission of New Drug Applications for pancreatic enzyme replacement therapy (PERT) products. Five oral delayed-release PERT products have been approved by the FDA, and several others are under development and/ or evaluation for New Drug Application submission. We present in this paper recommendations of the Cystic Fibrosis Foundation's Cystic Fibrosis (CF) Therapeutics Development Network and Data Safety Monitoring Board regarding study design considerations for evaluating PERT products in patients with CF. Careful attention to study design and accuracy of the outcome measures has confirmed our understanding of the efficacy and safety of PERT for the treatment of exocrine pancreatic insufficiency of CF.

Diagnosing malabsorption with systemic lipid profiling: pharmacokinetics of pentadecanoic acid and triheptadecanoic acid following oral administration in healthy subjects and subjects with cystic fibrosis

Objective: A Malabsorption Blood Test (MBT) is proposed as an alternative method to the 72-hour stool and dietary collection for assessing the degree of fat malabsorption in people with pancreatic insufficiency. The MBT consists of a simultaneous oral dose of pentadecanoic acid (PA), a free fatty acid, and triheptadecanoic acid (THA), a triglyceride with three heptadecanoic (HA) saturated fatty acids requiring hydrolysis by pancreatic lipase before HA can be intestinally absorbed. The aim of this study is to demonstrate the ability of MBT to detect fat malabsorption in healthy adult subjects using the pancreatic lipase (PL) inhibitor Orlistat (Xenical^®), and in subjects with CF and PI while on and off routine pancreatic enzyme doses. Materials and methods: The MBT with the PA and THA were delivered in a breakfast test meal (2.5 g PA and either 5 g or 8 g THA) to healthy adult subjects (ages 18 – 50 years, BMI 21 – 30) and to subjects with CF (> 12 years, FEV_1% predicted > 40%), after a 12-hour fast and 24 hours without dairy foods. Serum levels of PA and HA were assessed by gas-liquid chromatography, from blood samples drawn prior to MBT and then hourly for 8 hours. For healthy subjects, the MBT was administered before and after Orlistat treatment, and in subjects with CF, both with subjects receiving routine pancreatic lipase treatment (“on enzyme”) and also “off enzyme” treatment. Treatment groups were compared for baseline (C₀) and maximum (C_max) plasma concentrations of PA and HA over 8 hours: area under the curve (AUC) was calculated using linear trapezoid method. The ratio of HA to PA C_max and AUC was also calculated and compared. Results: For the healthy subjects (n = 15, 60% female, ages 21 – 49 years), absorption of HA was reduced 71% for C_max (p < 0.001) and 65% for AUC (p = 0.001) after Orlistat treatment, and absorption of PA was unchanged. For subjects with CF (n = 6, 50% female, ages 13 – 19 years), absorption of HA was minimal with subjects “off enzymes” and increased significantly with subjects “on enzymes” while absorption of PA did not differ between groups. Enzyme administration resulted in increased C_max HA/PA ratios from 0.02 to 0.92 and from 0.05 to 0.73 in subjects with CF receiving 5.0 g and 8.0 g of THA, respectively. AUC HA/PA ratios showed similar increases. Conclusions: In this pilot and feasibility proof-of-concept study, the MBT, utilizing the relative absorption of HA to PA, two odd-chained fatty acids, responds to changes in fat absorption in healthy subjects using a lipase inhibitor and in subjects with CF while on or off enzyme therapy. The MBT holds promise to provide a more accurate, specific and acceptable alternative to the 72-hour stool collection to quantify pancreatic-based fat malabsorption in a variety of clinical and research contexts.

Clinical utility of 13C-liver-function breath tests for assessment of hepatic function

13C-Liver-function breath tests have been used in clinical diagnostics and, to a limited extent, to investigate hepatic function. From a practical perspective, tests such as the 13C-aminopyrine and 13C-methacetin breath tests are simple to administer, safe, and relatively inexpensive to perform. Surprisingly, they have not entered the mainstream of clinical practice, because they are perceived to lack the specificity and adequate precision needed to give accurate results in real time. The dynamic nature of 13C-liver-function breath tests, their possible versatility in terms of assessing a range of different liver functions, and the ease with which they can be repeated to follow relative changes in liver function with time, all imply the potential for wider clinical application. Therefore, there is a need for these tests to be critically evaluated and their potential clinical application be tested systematically against defined objectives. We describe refinements in the methodology of the tests and propose several situations in which currently reliable methods for assessment of liver function do not exist and where 13C-liver-function breath tests might be of use. We propose that use has been constrained by practical methodological considerations which could be addressed to offer tests better suited to routine application in the out-patient or community setting.

(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.

Usefulness of a 13C-labeled mixed triglyceride breath test for assessing pancreatic exocrine function after pancreatic surgery

BACKGROUND

Although the fecal elastase-1 test is a satisfactory pancreatic exocrine function test, breath tests that use stable isotopes have been developed recently as alternatives. We evaluated the usefulness of a (13)C-labeled mixed triglyceride breath test for assessing pancreatic exocrine function after pancreatic surgery.

METHODS

The breath test and the fecal elastase-1 test were performed on 7 healthy volunteers, 10 patients with chronic pancreatitis, and 95 patients after pancreatic surgery. The breath test was analyzed with isotope ratio mass spectrometry and the cumulative recovery of (13)CO(2) at 7 hours (% dose (13)C cum 7h) was calculated. The fecal elastase-1 concentration was determined immunoenzymatically.

RESULTS

Both the fecal elastase-1 concentration and the % dose (13)C cum 7h of chronic pancreatitis patients and pancreatic resection patients were less than those of healthy volunteers. In all subjects, % dose (13)C cum 7h correlated with the fecal elastase-1 concentration (n = 112, R(2) = 0.14, P < .01). Accuracy rates for clinical symptoms, including clinical steatorrhea, for the fecal test and the breath test were 62 and 88%, respectively.

CONCLUSION

The (13)C-labeled mixed triglyceride breath test might be more useful than the fecal elastase-1 test for evaluating pancreatic exocrine function after pancreatic resection.

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.

An extract of black, green, and mulberry teas causes malabsorption of carbohydrate but not of triacylglycerol in healthy volunteers

BACKGROUND

In vitro studies suggest that extracts of black, green, and mulberry teas could interfere with carbohydrate and triacylglycerol absorption via their ability to inhibit alpha-amylase, alpha-glucosidase, sodium-glucose transporters, and pancreatic lipase.

OBJECTIVE

We measured breath hydrogen and 13CO2 to investigate the ability of an extract of black, green, and mulberry tea leaves to induce malabsorption of carbohydrate and triacylglycerol in healthy volunteers.

DESIGN

In a crossover design, healthy adult volunteers randomly ingested test meals with a placebo beverage or a preparation containing an extract of black (0.1 g), green (0.1 g), and mulberry (1.0 g) teas. One test meal contained 50 g carbohydrate as white rice, 10 g butter, and 0.2 g [13C]triolein, and the beverages contained 10 g sucrose. The calorie content of the second test meal consisted entirely of lipid (30 g olive oil and 0.2 g [13C]triolein). Breath-hydrogen and 13CO2 concentrations were assessed hourly for 8 h, and symptoms were rated on a linear scale.

RESULTS

With the carbohydrate-containing meal, the tea extract resulted in a highly significant increase in breath-hydrogen concentrations, which indicated appreciable carbohydrate malabsorption. A comparison of hydrogen excretion after the carbohydrate-containing meal with that after the nonabsorbable disaccharide lactulose suggested that the tea extract induced malabsorption of 25% of the carbohydrate. The tea extract did not cause triacylglycerol malabsorption or any significant increase in symptoms.

CONCLUSION

This study provides the basis for additional experiments to determine whether the tea extract has clinical utility for the treatment of obesity or diabetes.

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.

Diagnosis and treatment of intestinal malabsorption in cystic fibrosis

Intestinal malabsorption is severe and of early onset in virtually all people who have cystic fibrosis. The main cause is deficiency of pancreatic enzymes. Bicarbonate deficiency, abnormal bile salts, mucosal transport problems, motility differences, and anatomical structural changes are other contributory factors. Effective treatment should allow a normal to high-fat diet to be taken, control symptoms, correct malabsorption, and achieve a normal nutritional state and growth. Appropriate pancreatic enzyme replacement therapy will achieve normal or near-normal absorption in most people with cystic fibrosis. Early identification and treatment of intestinal malabsorption is critical to achieving optimal nutritional status. The occurrence of fibrosing colonopathy in a few patients on very high doses of those enzymes which have the copolymer Eudragit L30 D55 in their covering resulted in guidelines in the UK to avoid doses equivalent to more than 10,000 IU lipase per kg per day, and also to avoid preparations containing this copolymer in children and adolescents. For patients not responding to 10,000 IU lipase per kg per day review of adherence to treatment, change of enzyme preparation, variation in time of administration, and reduction in gastric acid may improve absorption. The importance of early investigation to exclude other gastrointestinal disorders as a cause of the patient's symptoms, rather than merely increasing the dose of enzymes, is stressed. With modern pancreatic enzymes in doses up to or only slightly in excess of 10,000 IU lipase per kg per day, adequate control of gastrointestinal symptoms and absorption can be achieved, and a normal nutritional state and growth rate maintained in most people with cystic fibrosis.

Analytical techniques in biomedical stable isotope applications: (isotope ratio) mass spectrometry or infrared spectrometry?

An overview is presented of biomedical applications of stable isotopes in general, but mainly focused on the activities of the Center for Liver, Digestive and Metabolic Diseases of the University Medical Center Groningen. The aims of metabolic studies in the areas of glucose, fat, cholesterol and protein metabolism are briefly explained, as well as the principle of breath testing and the techniques to study body composition and energy expenditure. Much attention is paid to the analytical considerations based upon metabolite concentrations, sample size restrictions, the availability of stable isotope labelled substrates and dose requirements in relation to compound-specific isotope analysis. The instrumental advantages and limitations of the generally used techniques gas chromatography/reaction/isotope ratio mass spectrometry and gas chromatography/mass spectrometry are described as well as the novelties of the recently commercialised liquid chromatography/combustion/isotope ratio mass spectrometry. The present use and future perspective of infrared (IR) spectrometry for clinical and biomedical stable isotope applications are reviewed. In this respect, the analytical demands on IR spectrometry are discussed to enable replacement of isotope ratio mass spectrometry by IR spectrometry, in particular, for the purpose of compound-specific isotope ratio analysis in biological matrices.

Comparison of accuracy and precision of heart rate calibration methods to estimate total carbon dioxide production during 13C-breath tests

BACKGROUND

13C-breath tests are noninvasive tools to measure gastrointestinal function and nutritional interventions. Calculation of percentage dose recovered of 13C in exhaled breath requires knowledge of CO2 production rate (VC02). A resting value is usually assumed, but this can underestimate VC02 because subjects are unlikely to remain at rest during tests that last for many hours. There is a need for a method to estimate nonresting VC02 during 13C-breath tests.

OBJECTIVE

To calibrate a heart rate monitor to continually estimate VC02 during 13C-breath tests.

DESIGN

Proof of concept study.

SUBJECTS

Eight healthy adults, 10 healthy children and six children with cystic fibrosis.

METHODS

Heart rate and VC02 were measured simultaneously at resting and nonresting levels. A new calibration method (smoothing heart rate and fitting a sigmoid function) was compared with published methods. A [ 3C]acetate breath test was used to demonstrate the range of physical activity during breath tests.

RESULTS

The new calibration method was more accurate than existing methods (mean bias -0.0002%, 95% confidence interval (CI) -0.0007, 0.0003% of the mean measured VC02). Smoothing heart rate gave a more precise estimate of VC02 and a more accurate estimate of resting energy expenditure (mean bias -0.09, 95% Cl -0.22, 0.05 mmol CO2 min-' m-2 body surface area) than using raw data (mean bias -0.21, 95% Cl -0.38, -0.04 mmol CO2 min' m-2 body surface area). Physical activity level ranged from 1.0 to 2.5 in children, and 1.0 to 1.5 in adults.

CONCLUSION

Use of smoothed HR with a sigmoid function provides an accurate method of estimating nonresting VC02 during 13C-breath tests.

Nutrition in patients with cystic fibrosis: a European Consensus

This document is the result of an European Consensus conference which took place in Artimino, Tuscany, Italy, in March 2001 involving 33 experts on nutrition in patients with cystic fibrosis, organised by the European Cystic Fibrosis Society, and sponsored by Axcan-Scandipharm, Baxter, Dr Falk Pharma, Fresenius, Nutricia, SHS International, Solvay Pharmaceuticals (major sponsor). The purpose of the conference was to develop a consensus document on nutrition in patients with cystic fibrosis based on current evidence.

Evaluation of the 13C-triolein breath test for fat malabsorption in adult patients with cystic fibrosis

BACKGROUND AND AIMS

A simple non-invasive test not requiring the use of radioactive isotopes is required to assess fat malabsorption in adult cystic fibrosis (CF) patients. Breath tests using substrates labeled with 13C meet these conditions. The 14C-triolein breath test is sensitive and specific for measuring fat malabsorption, but involves radiation exposure. The aim of this study was to examine the utility of a test using a 13C label and to determine whether pancreatic replacement therapy would return the test to the values of a normal control group.

METHODS

13CO2 recovery was assessed after an overnight fast in six adult patients with CF, both with and without pancreatic enzyme replacement therapy (PERT) in the usual dose for a light snack, in a randomized order, on different days. Studies were also performed in eight healthy volunteers after oral ingestion. Subjects drank 50 mL of a liquid meal mixed with 200 microL 13C-triolein and breath samples were collected by blowing through a straw into collection tubes every 30 min for 6 h. The effect of gastric emptying was assessed by comparison of oral ingestion with intraduodenal infusion. Intra-individual variability was assessed in nine volunteers by repeating the breath test after drinking the test meal on a separate day.

RESULTS

Compared with healthy subjects there was virtually no recovery of 13CO2 in CF patients without PERT. The median (interquartile range) cumulative percentage dose recovery (cPDR) at 6 h was 3% (0-8) in CF patients compared with 28% (22-41) in healthy controls (P < 0.01). Fat absorption was normalized (37%) (36-43) after ingestion of PERT. Gastric emptying delayed the peak in 13CO2 recovery, but there was no difference in the cPDR at 6 h. There was no difference in recovery between days 1 and 2.

CONCLUSIONS

The 13C-triolein breath test is a simple and reproducible method to measure fat malabsorption. The test provides a screening technique for fat malabsorption in adult CF patients and may be useful for monitoring the lowest effective dose of PERT.

Transient exocrine pancreatic insufficiency as a possible complication of an enterovirus infection

Exocrine pancreatic insufficiency is an exceptional problem in children, mostly associated with diseases like cystic fibrosis, Shwachman-Diamond syndrome or chronic pancreatitis, as is the case in idiopathic fibrosing pancreatitis. Many viral infections are known to cause acute pancreatitis. Most of them, however, are transient with no remaining damage. The differential diagnosis of persisting diarrhoea after gastrointestinal infection does not routinely include a search for exocrine pancreatic insufficiency.

CONCLUSION

This is the first description of a child with a transient but severe exocrine pancreatic insufficiency probably induced by an ordinary enterovirus infection

Production of 13C labelled pea flour for use in human digestion and fermentation studies

Stable isotope breath tests offer a new approach to the study of digestion and fermentation of carbohydrates in man. In this study, 13C labelled peas were grown by pulsing 250 ml 13CO2 into a sealed growth chamber. A second pulse was added to a portion of the peas to increase the 13C enrichment. This generated pea flour with an enrichment of 2.36 at.% excess (range 2.09-2.71 n = 3) and 8.64 atom % excess (range 7.37-9.78 n = 3) respectively. This represented incorporation of an absolute yield of 3.8% of the 13CO2 into peas in the 'once-labelled' treatment and 7.5% in the 'twice-labelled' treatment. Ingestion of a mixture of the labelled pea flour (300 mg) by two volunteers generated measurable 13CO2 excretion for breath test analysis. The profile of breath 13CO2 enrichment increased to a maximum within three hours after consuming the pea flour followed by a decrease almost back to baseline by 13 hours. Breath 13CO2 appeared to rise again after this apparent nadir at 13 hours until the end of the sampling period. Mathematical analysis of the data suggested that two peaks best described the profile of breath 13CO2 up to 13 hours. A third peak was necessary to describe the late rise in breath 13CO2 enrichment. This use of 13C enriched pea flour may provide a useful non invasive method for measurement of digestion and fermentation in vivo.

Analysis of 13C-mixed triacylglycerol in stool by bulk (EA-IRMS) and compound specific (GC/MS) methods

This paper was presented in poster form at the 17th International Congress of Nutrition, August 27-31, Vienna, Austria (Annals of Nutrition & Metabolism 2001; 45(Suppl.1):349). Some of the data were also presented in poster form at the British Society of Gastroenterology Meeting, March 18-21, Glasgow, UK (Gut 2001; 48(Suppl.1):A91). The 13C-mixed triacylglycerol (MTG) breath test is used to measure intraluminal fat digestion. In normal digestion, 20-40% of the ingested 13C label is recovered in breath CO2. We aimed to identify the proportions of ingested label excreted in stool, as well as breath following ingestion of 13C-MTG by children with impaired exocrine pancreatic function and healthy controls. 13C enrichment of breath samples was measured by continuous flow isotope ratio mass spectrometry (IRMS) and cumulative percent dose recovered (cPDR) in 10 h was calculated. Total 13C of a faecal fat extract from each stool was measured by elemental analyser-IRMS, and 13C enrichment and concentration of the TBDMS derivative of octanoic acid was measured by GC/MS after hydrolysis of the fat extract. Stool 5-day cPDR was calculated. Mean breath cPDR was 35%. Mean cPDR in stool by combustion-IRMS and GC/ MS, respectively, was 0.8% and 1.0%. Therefore, the remaining 64% of the 13C label must remain in the body and variability in breath cPDR is due to postabsorptive rather than predigestive factors.

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

BACKGROUND

Results from the 13C mixed triglyceride (MTG) breath test correlate with duodenal lipase activity in adults. This noninvasive test is a potential screening and diagnostic tool for children with fat malabsorption. The aim of this study was to adapt the methodology of the MTG breath test to study test meals and sampling methods and to define normal values for healthy children of all age groups; premature and full-term infants have similar pancreatic lipase deficiencies.

METHODS

After parental consent was obtained, 12 premature infants (< 37 weeks gestation and with body weights > 2 kg), 12 full-term infants (1-6 months old), 20 children (3-10 years old), and 20 teenagers (11-17 years old) were tested. All children were thriving well, had no gastrointestinal or respiratory problems, and had not received any medication that contained natural 13C. For the premature and full-term infants, a formula was prepared that had a low and stable natural 13C content mixed with 100 mg 13C-labeled MTG (1,3-distearyl, 2-[13C-carboxyl] octanoyl glycerol) and 1 g polyethylene-glycol 3350. The best accepted test meal for children over 3 years old was a slice of white bread with 5 g butter and 15 g chocolate paste, mixed with 250 mg 13C-labeled MTG, and a glass of 100 mL whole-fat milk. Children over 3 years old were able to blow through a straw in a vacutainer for collecting the breath samples. In children under 3 years old, expired air was collected by aspirating breath via a nasal prong. Carbon dioxide production was calculated according to weight, age, and sex.

RESULTS

For healthy pediatric control participants, the mean values for cumulative excretion of 13CO2 as a percentage of the administered dose after 6 hours were 23.9 +/- 5.2% in premature infants, 31.9 +/- 7.7% in full-term infants, 32.5 +/- 5.3% in children, and 28.0 +/- 5.4% in teenagers. The mean value for healthy adults is 35.6% with a lower reference limit of 22.8%.

CONCLUSIONS

Age-specific test meals and breath-sampling techniques for the MTG breath test were defined. The mean values for different age groups may serve as guidelines for normal values in the pediatric population. The cumulative values for expired 13CO2 were above the lower limit for adults, which suggests that preduodenal lipases compensates for pancreatic lipase deficiency in premature and full-term infants.

Control of malabsorption in cystic fibrosis

Intestinal malabsorption is severe and of early onset in virtually all people who have cystic fibrosis. The main cause is deficiency of pancreatic enzymes, but bicarbonate deficiency, abnormalities of bile salts, mucosal transport and motility, and anatomical structural changes are other contributory factors. Appropriate pancreatic replacement therapy will achieve normal or near normal absorption in many patients. It is important to identify both malabsorption and evidence of a pancreatic lesion in all patients who are to receive pancreatic enzymes. All who have evidence of fat malabsorption are deemed pancreatic insufficient and candidates for enzyme replacement therapy. Effective treatment should allow a normal diet to be taken, control symptoms, correct malabsorption and achieve a normal nutritional state and growth. The occurrence of fibrosing colonopathy in some patients receiving very high doses of those enzymes that have the copolymer Eudragit L30 D55 in their covering has resulted in guidelines in the UK to avoid dosages greater than the equivalent of 10,000 IU lipase/kg/day for all patients and also to avoid preparations containing this copolymer in children and adolescents. For patients not responding to 10,000 IU lipase/kg/day, review of adherence to treatment, change of enzyme preparation, variation of the time of administration and reduction in gastric acid may improve absorption. The importance of excluding other gastrointestinal disorders as a cause of the patient's symptoms and the need for early investigations, rather than merely increasing the dosage of enzymes, is stressed. With modern enzymes, adequate control of gastrointestinal symptoms and absorption can be achieved at dosages of 10,000 IU lipase/kg/day or only slightly more, and a normal nutritional state and growth rate maintained in most patients with cystic fibrosis.

Liver disease does not affect lipolysis as measured with the 13C-mixed triacylglycerol breath test in children with cystic fibrosis

BACKGROUND

Liver disease associated with cystic fibrosis may not only limit the solubilisation and absorption of the products of fat digestion, but also may depress the activity of pancreatic lipase. The purpose of this study was to measure the effect of liver disease on triacylglycerol lipolysis using the 13C-mixed triacylglycerol breath test.

METHODS

Forty children with cystic fibrosis took 13C-mixed triacylglycerol with a standard breakfast and the child's normal pancreatic enzyme replacement therapy. Breath samples were collected before and every 30 minutes after ingestion for 6 hours. The cumulative percentage dose of 13C recovered at 6 hours was calculated from sequential measurements of 13C enrichment of breath CO2, measured by isotope ratio mass spectrometry. Liver abnormalities and portal hypertension were defined by ultrasound scan and clinical examination.

RESULTS

Twenty-four children had liver abnormalities, including 5 with portal hypertension. No difference was found between cumulative percentage dose of 13C recovered at 6 hours in 16 children with no liver abnormality (mean, 21.4%+/-11.1%), 19 children with liver abnormalities (22.2%+/-10.0%) and 5 children with portal hypertension (20.9%+/-7.1%).

CONCLUSION

Intestinal lipolysis is not reduced in cystic fibrosis liver disease when measured using the 13C mixed triacylglycerol breath test. These findings affirm the test's use as an indirect measure of fat digestion that is not affected by inadequate intraluminal bile salts or liver disease.

Validation in an animal model of the carbon 13-labeled mixed triglyceride breath test for the detection of intestinal fat malabsorption

OBJECTIVE

To determine, in a rat model of fat malabsorption, the potency of the carbon 13-labeled mixed triglyceride ((13)C-MTG) breath test as a noninvasive, patient-friendly replacement for classic fat balance studies.

STUDY DESIGN

Comparison of the percentage of fat absorption, detected by fat balance, with the (13)CO(2) recovery of the (13)C-MTG breath test in rats fed high-fat chow and varying amounts of the lipase inhibitor, orlistat (0, 50, 200, and 800 mg per kilogram of chow), for 5 days.

RESULTS

On orlistat administration, total fat absorption decreased from 80.2% +/- 2.2% to 32.8% +/- 3.7% (mean +/- SEM, 0 mg and 800 mg of orlistat per kilogram of chow, respectively; P <.001). Correspondingly, breath (13)CO(2) recovery from (13)C-MTG at 6 hours decreased from 84.5% +/- 7.8% to 42.0% +/- 1.5% of the dose (0 mg and 800 mg of orlistat per kilogram of chow, respectively; P <.001). The 6-hour recovery of breath (13)CO(2) appeared to be highly correlated with the percentage of fat absorption (r = 0.88, P <.001). In rats with fat absorption higher than 70%, however, the coefficient of variation of the (13)C-MTG breath test was 3-fold larger than that of the fat balance.

CONCLUSIONS

The (13)C-MTG breath test could potentially replace the fat balance method for comparing fat absorption efficacy between groups. Yet, a considerable interindividual variation of the (13)C-MTG breath test under conditions of relatively mild fat malabsorption does not support its application for diagnostic purposes in individuals.

Triglyceride oxidation in cystic fibrosis: a comparison between different 13C-labeled tracer substances

BACKGROUND

For indirect evaluation of pancreatic lipase activity in cystic fibrosis, different 13C-labeled triglycerides may be used.

METHODS

Triglyceride oxidation in patients with cystic fibrosis was investigated after administration of different 13C-labeled triglycerides by comparing 13CO2 breath exhalation. In the comparative study, five patients with cystic fibrosis (age, 8-15 years; body weight, 22.5-39.8 kg) were treated with Pangrol (individual dosages: 1-3 capsules per morning meal; Berlin-Chemie, Berlin, Germany). [1,1,1-13C3]Glyceryl tripalmitate and [1,1,1-13C3]glyceryl trioleate were administered as a single oral pulse at 8:00 A.M. (dosage, 4 mg/kg each) with the standard diet Fresubin (dosage, 10 ml/kg; Fresenius, Bad Homburg, Germany). Alternately, the same subjects were given the synthetic mixed triglyceride 1,3-distearyl, 2[13C]octanoyl glycerol (dosage, 12.5 mg/kg) contained in the standard diet Nutri-Mix (dosage, 10 ml/kg; Nutricia, Zoetemeer, The Netherlands). Breath samples were taken in 15- and 30-minute intervals over 8 hours. The 13CO2 enrichment was measured by continuous-flow isotope ratio mass spectrometry.

RESULTS

After administration of the 13C-labeled tripalmitin-triolein mixture and the mixed triglyceride, mean maximum 13CO2 enrichments were 4.70 and 7.37 delta over baseline, occurring at 7.0 and 3.5 hours, respectively. The corresponding percentage cumulative 13CO2 exhalations were 12.25% and 29.19%, respectively, and differed significantly in the five paired subjects (p = 0.003).

CONCLUSIONS

After using different 13C-labeled triglycerides the resultant 13CO2 exhalation reflected the triglyceride hydrolysis and subsequent oxidation. It is concluded that the different cumulative 13CO2 exhalations were mainly caused by the rate-limiting step of triglyceride hydrolysis to free fatty acids and 2-monoglycerides and by fat deposition. Noninvasive 13C breath tests using different 13C-labeled triglycerides can be used for evaluation of pancreatic lipase activity before and during enzyme supplementation.

Development of fat digestion in infancy

AIM

To measure the development of fat digestion in early life, using a stable isotope breath test.

METHODS

A combined longitudinal and cross sectional study was performed on 30 term and preterm infants using 13C-labelled mixed triglyceride (MTG). Seventy six tests were performed in all. Results were expressed as cumulative percentage dose recovered over 6 hours (cPDR).

RESULTS

Eighteen of 34 tests performed on infants under 30 days of age showed cPDRs below the normal range for adults and older children. The remainder of tests, performed on infants over 57 days of age, all showed cPDRs within the normal range. Peak PDR correlated significantly (r = 0. 928, p<0.01) with cPDR.

CONCLUSION

The capacity to digest fat is incomplete at birth, but quickly develops to normal levels during the first months of life. The MTG breath test is a useful non-invasive method to measure the development of fat digestion in early life.

Prevalence of Helicobacter pylori infection detected by serology and 13C-urea breath test in HIV-1 perinatally infected children

BACKGROUND

Conflicting results have been reported in adults with human immunodeficiency virus (HIV-1) who were investigated for Helicobacter pylori infection. Most studies indicate a lower prevalence than is found in the general population. The purposes of this study were to evaluate H. pylori prevalence by noninvasive methods in a population of children perinatally infected with HIV-1 and to correlate H. pylori prevalence with HIV-1-related clinical and immunologic status.

METHODS

H. pylori infection was studied in 45 children perinatally infected with HIV-1 by performing serologic testing of anti-H. pylori immunoglobulin G antibodies and the 13C-urea breath test.

RESULTS

Eight children with HIV-1 (17.7%) were positive by serology, and nine (20%) were positive by 13C-urea breath test. No significant differences related to age, previous antibiotic treatment, immunoglobulin administration, antiretroviral treatment, abdominal pain, CD4+ cell count, number of HIV-1 RNA copies, and frequency of severe immunodepression were noted between children with positive 13C-urea breath test results and those with negative results. Children with positive results were significantly more likely to have severe clinical manifestations.

CONCLUSIONS

The results show, by both serology and 13C-urea breath test, a prevalence of H. pylori infection comparable with the prevalence in the normal population of the same age. H. pylori prevalence has probably been underestimated in patients with HIV. Results of serologic and histologic analyses for H. pylori require cautious interpretation, especially in severely immunodeficient patients.

Fat malabsorption in cystic fibrosis patients receiving enzyme replacement therapy is due to impaired intestinal uptake of long-chain fatty acids

BACKGROUND

Pancreatic enzyme replacement therapy frequently fails to correct intestinal fat malabsorption completely in cystic fibrosis (CF) patients. The reason for this failure is unknown.

OBJECTIVE

We investigated whether fat malabsorption in CF patients treated with pancreatic enzymes is caused by insufficient lipolysis of triacylglycerols or by defective intestinal uptake of long-chain fatty acids.

DESIGN

Lipolysis was determined on the basis of breath 13CO2 recovery in 10 CF patients receiving pancreatic enzyme replacement therapy after they ingested 1.3-distearoyl,2[1-13C]octanoyl glycerol ([13C]MTG). Intestinal uptake of long-chain fatty acids was determined by analyzing plasma [13C]linoleic acid ([13C]LA) concentrations after patients ingested [13C]LA. For 3 d, dietary intakes were recorded and feces were collected.

RESULTS

Fecal fat excretion ranged from 5.1 to 27.8 g/d (mean+/-SD: 11.1+/-7.0 g/d) and fat absorption ranged from 79% to 93% (89+/-5%). There was no relation between breath 13CO2 recovery and dietary fat absorption (r = 0.04) after ingestion of [13C]MTG. In contrast, there was a strong relation between 8-h plasma [13C]LA concentrations and dietary fat absorption (r = 0.88, P < 0.001).

CONCLUSION

Our results suggest that continuing fat malabsorption in CF patients receiving enzyme replacement therapy is not likely due to insufficient lipolytic enzyme activity, but rather to incomplete intraluminal solubilization of long-chain fatty acids, reduced mucosal uptake of long-chain fatty acids, or both.

Stable isotope breath tests

There is a need for non-invasive tests of gastrointestinal and nutritional function. Clinical problems peculiar to infancy and childhood require prompt diagnosis, and methods that are invasive or involve the use of radioisotopes are often impractical or ethically unacceptable. What the pediatrician and clinical scientist seek are tests that are simple, repeatable, and unequivocal in their result for diagnosis, to assess the effects of treatment, and to measure the development of gastrointestinal function during early life. Stable isotope breath tests offer a ready and attractive answer to these needs. They involve the ingestion of substrates labeled with the non-radioactive isotope of carbon (13C), followed by the collection of serial breath samples for analysis of the enrichment of 13CO2, the end product of substrate metabolism. Their non-invasive nature recommends them for use in infancy and childhood, and they can be performed in the ward, clinic, laboratory, and home. In this article I discuss to what degree stable isotope breath tests fulfill the pediatrician's and scientist's needs. I have chosen two examples from the work of myself and my colleagues to illustrate the principles and use of 13C breath tests to detect Helicobacter pylori infection and to measure fat digestion in infancy and childhood.

Analysis of tert.-butyldimethylsilyl [1-13C]palmitic acid in stool samples by gas chromatography-mass spectrometry with electron impact ionisation: comparison with combustion isotope-ratio mass spectrometry

The use of 13C-labelled compounds to study lipid metabolism is increasing. Typically less than 40% of the orally administered label is recovered in breath CO2. The remainder must be either absorbed and not oxidised or not absorbed and remain in the faeces. Two methods of determining how much tracer passes through the body, and is present in the stool, were compared. Compound specific analysis of tert.-butyldimethylsilyl [13C]hexadecanoic acid by gas chromatography-mass spectrometry (GC-MS) with electron impact ionisation was compared with bulk analysis of whole stool and lipid extract by continuous flow isotope ratio mass spectrometry (CF-IRMS) with a combustion interface. The mean difference between the IRMS and GC-MS methods was -0.02 mmol 13C d(-1) with a mean excretion of 14.2 mmol 13C d(-1). Combustion IRMS is both simpler and cheaper, when the objective is to determine how much administered dose appears in stool, and information about the form of the label is not required.

Metabolic handling of 13C labelled tripalmitin in healthy controls and patients with cystic fibrosis

AIM

To examine the gastrointestinal handling and metabolic disposal of emulsified [1-13C]palmitic acid esterified into a triglyceride in nine healthy children and seven patients with cystic fibrosis on enzyme replacement treatment.

METHODS

After an overnight fast, each child was given 10 mg/kg body weight [1,1,1-13C]tripalmitin with a standardised test meal of low natural 13C abundance. The total enrichment of 13C was measured using isotope ratio mass spectrometry in stool collected for a period of up to five days and in breath samples collected over a 24 hour period.

RESULTS

The mean proportion of administered 13C label excreted in stool was 6% (range, 1-12.7%) in healthy children and 24.6% (range, 0-64%) in patients with cystic fibrosis. Healthy children excreted 31.3% of the administered label on their breath (range, 14.2-42.9%). Correcting the excretion of administered 13C label on the breath for differences in digestion and absorption in patients with cystic fibrosis increased the difference between individuals from 0-31.3% of administered dose (mean, 17.9%) to 0-49.1% of absorbed dose (mean, 23.2%) and was poorly related to the amount of 13C label in stool.

CONCLUSION

Measurements of breath 13CO2 do not consistently reflect the gastrointestinal handling of emulsified 13C labelled tripalmitin because of differences in digestion and absorption in cystic fibrosis. Further studies need to examine whether "breath tests" alone can predict with confidence the gastrointestinal handling of other 13C labelled triglycerides and fatty acids.

Importance of measuring CO2-production rate when using 13C-breath tests to measure fat digestion

Stable isotope breath tests offer a safe, repeatable non-invasive method of measuring fat digestion. They involve the ingestion of a substrate labelled with 13C followed by serial measurements of the 13C:12C ratio in expired CO2, from which the percentage of the 13C dose recovered (PDR) can be calculated. However PDR depends on the CO2-production rate. Our aim was to compare results obtained using directly measured CO2-production rates with those calculated from two predicted values. Twelve normal healthy children and twenty-four children with cystic fibrosis (CF) (without or with the normal dose of enzyme supplementation) were studied with 1,3-distearyl, 2[carboxyl-13C] octanoyl glycerol. The volume of CO2 produced (litres/min) was measured at rest for 30 min approximately 3 h after substrate ingestion, and the results were converted to mmol/min. For each subject the expected BMR was calculated from the equation of Schofield (1985), based on sex, age, weight and height, and from these values, CO2-production rate was derived. Surface area was calculated and an estimated value of 5 mmol/m2 per min (Shreeve et al. 1970) was used. Using these three CO2-production rates, three different PDR were calculated and compared. In healthy children there was a close concordance between measured and predicted CO2-production rates, but children with CF had a mean measured CO2-production rate 39% higher than normal children. This use of normal data for predicted CO2-production rates in children with CF underestimates cumulative PDR. If direct measurements of CO2-production rate are not available or impossible to perform the VCO2 obtained from the BMR calculated using the equations of Schofield (1985) or Shreeve et al. (1970) can be used in normal children. However, if accurate results for PDR are to be obtained, CO2-production rates should be measured when performing breath tests in conditions where energy expenditure and/or CO2-production rate are not expected to be normal.

Bile salt-stimulated lipase and digestion of non-breast milk fat

BACKGROUND

13 Carbon (13C)-lipid breath tests are an effective, noninvasive way of repeatedly measuring fat digestion. The purpose of this study was to assess the contribution of bile salt-stimulated lipase (BSSL) in human milk to the digestion of non-breast-milk fat in Gambian infants.

METHODS

Twelve Gambian infants (aged 3-8 months) were studied on 4 days. 13C-Trioctanoin (7.5 mg/kg, digested by BSSL preduodenal and pancreatic lipases) and 13C-cholesteryl octanoate (25 mg/kg, digested by BSSL and pancreatic lipases) were used as substrates. The percentage dose recovery (PDR) of 13C in breath during 5 hours was compared after ingestion of each substrate with fresh, expressed breast milk (FBM) or heated, expressed breast milk (HBM). Gas isotope ratio-mass spectrometry was used to measure 13C enrichment, and breast milk samples were analysed for esterase activity.

RESULTS

Heating breast milk significantly decreased esterase activity (mean +/- SD values: FBM = 12.2 +/- 2.9 IU/ml; HBM = 0.5 +/- 0.3 IU/ml), and there was no difference in the volumes of milk ingested on each test day (approximately 50 ml). The PDR of 13C was comparable to that previously described in healthy English infants and was not increased by BSSL. The mean +/- SD PDR of 13C from trioctanoin was 36.3 +/- 8.4% for FBM and 34.6 +/- 6.3% for HBM (NS). From cholesteryl octanoate, the mean +/- SD PDR of 13C was 24.3 +/- 8.7% for FBM and 27.1 +/- 7.5% for HBM (NS).

CONCLUSIONS

Bile salt-stimulated lipase may enhance fat digestion in younger or malnourished infants who have a greater degree of pancreatic enzyme deficiency. However, this study suggests that it does not increase the digestion of non-breast-milk fat in healthy, well-nourished infants aged 3 to 8 months from an underprivileged background, who typically ingest frequent small quantities of breast milk.