Exocrine pancreatic insufficiency: accuracy and clinical value of the uniformly labelled 13C-Hiolein breath test

Exocrine pancreatic insufficiency: prevalence, diagnosis, and management

Exocrine pancreatic insufficiency (EPI) is a condition caused by reduced or inappropriate secretion or activity of pancreatic juice and its digestive enzymes, pancreatic lipase in particular. EPI can result in clinical manifestation and biochemical alterations causing reduced quality of life and life-threating complications. EPI is common in pancreatic disorders, where it should be suspected and actively investigated, and in many extrapancreatic conditions. There are various tests available to diagnose EPI, with indirect, noninvasive ones, such as concentration of fecal elastase being more commonly employed. Administration of pancreatic enzymes replacement therapy remains the mainstay of EPI treatment. The present review article will discuss current evidence regarding the prevalence of EPI, the available tests to diagnose it and its treatment.

Gastro 2013 APDW/WCOG Shanghai working party report: chronic diarrhea: definition, classification, diagnosis

Diarrhea is best defined as passage of loose stools often with more frequent bowel movements. For clinical purposes, the Bristol Stool Form Scale works well to distinguish stool form and to identify loose stools. Laboratory testing of stool consistency has lagged behind. Acute diarrhea is likely to be due to infection and to be self-limited. As diarrhea becomes chronic, it is less likely to be due to infection; duration of 1 month seems to work well as a cut-off for chronic diarrhea, but detailed scientific knowledge is missing about the utility of this definition. In addition to duration of diarrhea, classifications by presenting scenario, by pathophysiology, and by stool characteristics (e.g. watery, fatty, or inflammatory) may help the canny clinician refine the differential diagnosis of chronic diarrhea. In this regard, a careful history remains the essential part of the evaluation of a patient with diarrhea. Imaging the intestine with endoscopy and radiographic techniques is useful, and biopsy of the small intestine and colon for histological assessment provides key diagnostic information. Endomicroscopy and molecular pathology are only now being explored for the diagnosis of chronic diarrhea. Interest in the microbiome of the gut is increasing; aside from a handful of well-described infections because of pathogens, little is known about alterations in the microbiome in chronic diarrhea. Serological tests have well-defined roles in the diagnosis of celiac disease but have less clearly defined application in autoimmune enteropathies and inflammatory bowel disease. Measurement of peptide hormones is of value in the diagnosis and management of endocrine tumors causing diarrhea, but these are so rare that these tests are of little value in screening because there will be many more false-positives than true-positive results. Chemical analysis of stools is of use in classifying chronic diarrhea and may limit the differential diagnosis that must be considered, but interpretation of the results is still evolving. Breath tests for assessment of carbohydrate malabsorption, small bowel bacterial overgrowth, and intestinal transit are fraught with technical limitations that decrease sensitivity and specificity. Likewise, tests of bile acid malabsorption have had limited utility beyond empirical trials of bile acid sequestrants.

Enzyme replacement therapy for pancreatic insufficiency: present and future

Pancreatic enzyme replacement therapy is currently the mainstay of treatment for nutrient malabsorption secondary to pancreatic insufficiency. This treatment is safe and has few side effects. Data demonstrate efficacy in reducing steatorrhea and fat malabsorption. Effective therapy has been limited by the ability to replicate the physiologic process of enzyme delivery to the appropriate site, in general the duodenum, at the appropriate time. The challenges include enzyme destruction in the stomach, lack of adequate mixing with the chyme in the duodenum, and failing to deliver and activate at the appropriate time. Treatment is begun when clinically significant malabsorption occurs resulting in steatorrhea and weight loss. Treatment failure is addressed in a sequential fashion. Current research is aimed at studying new enzymes and delivery systems to improve the efficiency of action in the duodenum along with developing better means to monitor therapy.

(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.

Diagnosis of chronic pancreatitis: Functional testing

The diagnosis of chronic pancreatitis is mainly based on imaging procedures (e.g., endoscopic ultrasound, magnetic resonance cholangiopancreatography (MRCP) and magnetic resonance imaging (MRI)). Functional testing in this context could however be still of help in cases of inconclusive morphological findings. With this aim, only the secretin-pancreozymin test and the endoscopic test are sensitive enough. The role of other function tests, such as the quantification of the coefficient of fat absorption (CFA) and the (13)C-mixed triglyceride breath test, is limited to the diagnosis of exocrine pancreatic insufficiency with maldigestion. Faecal elastase and chymotrypsin are still useful for detecting reduction of pancreatic secretion in patients with different pancreatic diseases and patients' compliance to enzyme replacement therapy, respectively. Other tests used in the past (e.g., Lundh test, N-benzoyl-tryosyl para-aminobenzoic acid (NBT-PABA) test, pancreolauryl test and amino acid consumption test) are neither available now nor useful for clinical practice. This article reviews the different pancreatic function tests commercially available and their role in clinical practice.

Methods and functions: Breath tests

Breath tests provide a valuable non-invasive diagnostic strategy to in vivo assess a variety of enzyme activities, organ functions or transport processes. Both the hydrogen breath tests and the (13)C-breath tests using the stable isotope (13)C as tracer are non-radioactive and safe, also in children and pregnancy. Hydrogen breath tests are widely used in clinical practice to explore gastrointestinal disorders. They are applied for diagnosing carbohydrate malassimilation, small intestinal bacterial overgrowth and for measuring the orocecal transit time. (13)C-breath tests non-invasively monitor the metabolisation of a (13)C-labelled substrate. Depending on the choice of the substrate they enable the assessment of gastric bacterial Helicobacter pylori infection, gastric emptying, liver and pancreatic function as well as measurements of many other enzyme activities. The knowledge of potential pitfalls and influencing factors are important for correct interpretation of breath test results before drawing clinical conclusions.

Usefulness of breath test for evaluating pancreatic exocrine function using N-benzoyl-L-tyrosyl-1-13C-L-alanine sodium in non-invasive and conscious rats

N-Benzoyl-L-tyrosyl-1-13C-L-alanine sodium is a dipeptide used for evaluating pancreatic exocrine function. The method of evaluation, however, is not yet satisfactory, especially in experimental animals. The relation between diabetes and pancreatic exocrine function also is not clear. Therefore, this study sought to establish a method for evaluating pancreatic exocrine function and to validate the method by determining non-invasively the effect of alloxan-induced diabetes in conscious rats. After fasting, rats were orally administered Racol containing N-benzoyl-L-tyrosyl-1-13C-L-alanine sodium or 1-13C-L-alanine and housed in desiccators. The expired air in the desiccator was collected in a breath-sampling bag using a tube and aspiration pump, and the level of 13CO2 in this air was measured using an infrared spectrometer at appropriate intervals over a 120 min period. The rate of 13CO2 excretion increased, peaked and then decreased in a dose-dependent manner. The maximum concentration and area under the curve of 13CO2 excretion significantly and positively correlated with the doses of N-benzoyl-L-tyrosyl-1-13C-L-alanine sodium. In the rats made diabetes by the administration of alloxan, the level of expired 13CO2 air changed at significantly lower levels as compared with that of the control rats on day 3, although the level of expired 13CO2 air from 1-13C-L-alanine was also markedly lower than that of the control rats. These results showed that pancreatic exocrine function can be evaluated using this breath test system and that alloxan-induced diabetes affects this function.

Evaluation of pancreatic exocrine secretion using 13C-dipeptide (benzoyl-L-tyrosyl-[1-(13)C]alanine) breath test: focusing on pancreatoduodenectomy cases

OBJECTIVES

We investigated whether a breath test using benzoyl-L-tyrosyl-[1-(13)C]alanine (Bz-Tyr-Ala) allows assessment of pancreatic exocrine function.

METHODS

Benzoyl-L-tyrosyl-[1-(13)C]alanine was orally administered, and changes in (13)CO2 were expressed as delta per thousand. The breath test was performed in chronic pancreatitis patients and healthy subjects in a preliminary study and, subsequently, in 17 pancreatoduodenectomy patients, to examine the difference between the results obtained at the times of pancreatic tube insertion and removal, the relationship between breath test results after tube removal and the volume of pancreatic juice drained, and the difference in results between the presence versus the absence of histological changes of chronic pancreatitis.

RESULTS

The delta per thousand was lower in the chronic pancreatitis patients than in healthy subjects. In the postoperative patients, the delta per thousand was higher at tube insertion than at tube removal. The correlations of the delta per thousand with the maximum volume of pancreatic juice, its mean volume, and pancreatic juice amylase levels were 0.865, 0.757, and 0.853, respectively. The delta per thousand was lower in 11 patients with that in 6 patients without histological changes of chronic pancreatitis.

CONCLUSIONS

These results suggest that the Bz-Tyr-Ala breath test can measure pancreatic exocrine function.

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.

Synthetic 13C-dipeptide breath test for the rapid assessment of pancreatic exocrine insufficiency in rats

OBJECTIVE

(13)C-breath tests have been investigated in order to assess pancreatic exocrine function using various (13)C-compounds, but they have not been accepted for routine clinical use. One of the barriers to their acceptance is that these tests are time-consuming and require up to several hours for breath collection. The purpose of this study was to design a novel (13)C-compound that would make a rapid (13)C-breath test for assessing exocrine pancreatic function possible.

MATERIAL AND METHODS

N-benzoyl-L-tyrosyl-1-(13)C-L-alanine was synthesized, and the characteristics of its cleavage in duodenal juice and in the duodenum of rats were examined. Thereafter, a (13)C-breath test was carried out in which N-benzoyl-L-tyrosyl-1-(13)C-L-alanine was given orally to pancreatic exocrine-insufficient and normal control rats.

RESULTS

N-benzoyl-L-tyrosyl-1-(13)C-L-alanine was readily cleaved and liberated 1-(13)C-L-alanine in the duodenal juice. Carboxypeptidase was a major contributor to the cleavage. When N-benzoyl-L-tyrosyl-1-(13)C-L-alanine was injected into the duodenum and orally administered to the rats, the (13)C atom% of CO(2) in breath increased rapidly. This indicated that N-benzoyl-L-tyrosyl-1-(13)C-L-alanine in the duodenum liberated (13)C-Ala on cleavage. (13)C-Ala is absorbed and metabolized to liberate (13)CO(2), which is exhaled. It was shown that the Delta(13)CO(2) ( per thousand) in the N-benzoyl-L-tyrosyl-1-(13)C-L-alanine breath test in the pancreatic exocrine-insufficient rats, in whom the absorption and metabolism of (13)C-Ala was unimpaired, was significantly lower than that in the control rats.

CONCLUSIONS

The rate of increase in the Delta(13)CO(2) ( per thousand) in the N-benzoyl-L-tyrosyl-1-(13)C-L-alanine breath test is expected to be proportional to the rate of N-benzoyl-L-tyrosyl-1-(13)C-L-alanine cleavage by pancreatic proteases in the duodenum. We propose the N-benzoyl-L-tyrosyl-1-(13)C-L-alanine breath test as a rapid test for assessing pancreatic exocrine function.

Measurement of extra-pancreatic secretory function by 13C-dipeptide breath test

A simple breath test was developed for assessment of exocrine pancreatic function employing 13C-dipeptide [ie, benzoyl-L-tyrosyl-[1-(13)C]alanine (Bz-Tyr-Ala)], and this test was examined to determine whether it can be used to diagnose exocrine pancreatic insufficiency in patients with chronic pancreatitis. The subjects, 24 patients with chronic pancreatitis and 16 healthy adult controls, underwent the Bz-Tyr-Ala breath test, in which breath samples were collected every 10 min up to 90 min after oral administration of an aqueous solution of 5-mg/kg Bz-Tyr-Ala (7 mM). They also underwent a breath test with [1-(13)C]alanine equimolar to that contained in Bz-Tyr-Ala and the N-benzoyl-L-tyrosyl-p-aminobenzoic acid (BT-PABA) test. Delta13CO2 values at 10-60 min for the Bz-Tyr-Ala breath test were significantly lower in chronic pancreatitis patients than in normal controls. However, the [1-(13)C]alanine breath test results did not differ between patients and normal controls. The correlation coefficient between the Bz-Tyr-Ala breath test Delta13CO2 value at 20 min, and the results of the BT-PABA test were r=0.726 (r2=0.527, P<0.0001). The results suggest that this newly developed Bz-Tyr-Ala breath test can quickly and noninvasively diagnose the exocrine pancreatic dysfunction.

13C-mixed triglyceride breath test to assess oral enzyme substitution therapy in patients with chronic pancreatitis

BACKGROUND & AIMS

Malnutrition persists in most patients with chronic pancreatitis despite an adequate clinical response to oral pancreatic enzyme substitution therapy. Our aims were to analyze the accuracy of the 13C-mixed triglyceride breath test as a tool for evaluating the effect of enzyme therapy on fat digestion in chronic pancreatitis, and to analyze the impact of modifying the therapy according to the breath test on patients' nutritional status.

METHODS

The accuracy of the breath test for monitoring the effect of therapy was evaluated prospectively in 29 patients with maldigestion secondary to chronic pancreatitis by using the coefficient of fat absorption as the gold standard. Therapy was modified to obtain a normal breath test result in a further 20 chronic pancreatitis patients with malnutrition despite an adequate clinical response to the enzyme therapy; the impact of this therapeutic modification on patients' nutritional status was evaluated.

RESULTS

The coefficient of fat absorption and breath test results were similar when assessing fat absorption before and during treatment. Modification of the enzyme therapy to normalize fat absorption as assessed by the breath test in the second group of 20 patients was associated with a significant increase of body weight (P < .001), and serum concentrations of retinol binding protein (P < .001) and prealbumin (P < .001).

CONCLUSIONS

The 13C-mixed triglyceride breath test is an accurate method to evaluate the effect of enzyme therapy on fat digestion. This method is simpler than the standard fecal fat test to assess therapy in patients with pancreatic exocrine insufficiency. Normalizing fat absorption improves nutrition in these patients.

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.

Low-dose gluten challenge in celiac sprue: malabsorptive and antibody responses

BACKGROUND & AIMS

Undiagnosed patients with symptoms of celiac sprue often present to physicians after establishing dietary gluten exclusion. Although they must resume a gluten-containing diet for evaluation, there are no guidelines regarding duration of the gluten challenge, gluten dose, or monitoring parameters. We investigated the effects of a short-term gluten challenge in asymptomatic treated adult celiac patients on intestinal absorption and celiac antibody tests.

METHODS

Eight adult asymptomatic celiac patients consumed either 5 or 10 g of partially hydrolyzed gluten per day in an orange juice mixture for 21 days while maintaining their usual gluten-free diet. A symptom questionnaire, serum antibodies (antigliadin immunoglobulin [Ig]A and antitransglutaminase IgA and IgG), D-xylose urine excretion test, and 72-hour quantitative fecal fat test were monitored.

RESULTS

Two patients (25%) had at least 1 abnormal celiac antibody test at baseline. There was no increase in antibodies during gluten exposure compared with baseline for any of the patients (P > .05). At baseline, 1 patient had abnormal urine xylose excretion, and 3 patients had abnormal fecal fat values. At day 15 of gluten challenge, all patients had reduced xylose absorption compared with baseline (P = .0019), and 5 of 8 participants (63%) reduced their xylose excretion to the abnormal range. Seven of 8 patients (88%) had increased fecal fat excretion at day 15 (P = .026), and 6 of these (75%) had steatorrhea by day 15.

CONCLUSIONS

Short-term gluten challenge in asymptomatic adult celiac patients produces carbohydrate and fat malabsorption but does not increase transglutaminase and antigliadin antibody titers.

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.

An inter- and intra-laboratory comparison of breath ¹³CO₂analysis

BACKGROUND

¹³C breath test analysis requires accurate ¹³CO₂measurements.

AIM

To perform a multicentre study to evaluate the repeatability and reproducibility of breath ¹³CO₂analysis.

METHODS

Two series of 25 paired randomly coded tubes (each consisting of 23 ¹³CO₂-enriched breath samples and two samples of standard reference pure CO₂with certified δ ¹³C(PDB)) were sent to participating centres for ¹³CO₂measurement. Each series of tubes was analysed 10 days apart. The repeatability and reproducibility of ¹³C measurements was assessed by Mandel's k and h statistics.

RESULTS

Twenty-two centres participated in the study: 18 showed good inter- and intra-laboratory variability, whilst four showed abnormally high inter- or intra-laboratory variability. Breath test results were also significantly affected by the accuracy of the ¹³C analytical procedures.

CONCLUSIONS

A low accuracy of ¹³C measurements may significantly affect the results of breath tests, leading to inappropriate clinical decisions. Standardization of ¹³C analysis is required to guarantee optimal ¹³C measurements and accurate ¹³C breath test results.

Review article: Pancreatic function testing

Pancreatic function tests are most commonly used to diagnose chronic pancreatitis. These tests include tests which document exocrine or endocrine gland insufficiency and tests which instead measure gradations of decreased secretory capacity. The tests in the former category generally become abnormal when advanced, longstanding chronic pancreatitis is present. Tests in the latter category, however, have the potential to detect chronic pancreatitis at an earlier stage than other available diagnostic tests, including commonly used imaging tests such as computed tomography and endoscopic retrograde cholangiopancreatography. This potential advantage of diagnostic sensitivity is, however, counterweighed by the fact that these tests which measure stimulated secretory capacity are only available at a very few referral centres. This article will review the variety of pancreatic function tests and describe their rationale, accuracy, cost, and clinical usefulness.

Modern diagnostics of chronic pancreatitis

Chronic pancreatitis is a well-defined disease on histopathological grounds, but for clinical purposes diagnosis is generally not based on histological specimens. Imaging procedures, non-invasive or with different degrees of invasiveness, and pancreatic function tests are therefore the diagnostic mainstay in patients with suggestive clinical history. The correct diagnosis of chronic pancreatitis is easy in late stages but difficult in an early stage of the disease. A particular challenge is the differentiation between acute or recurrent acute and early chronic pancreatitis. Earlier classifications (Cambridge and Marseille) did not consider the complex interrelationship between (especially alcoholic) acute and chronic pancreatitis. A possible solution is to separate the entities into probable and definite alcoholic chronic pancreatitis, with the assignment into the latter category achieved by follow-up investigations. Up to now the best diagnostic accuracy at an early stage is achieved by the detection of abnormalities of the ductal system in endoscopic retrograde pancreatography or by assessing exocrine function with the secretin-ceruletide test. The endoscopic ultrasound may substitute the endoscopic retrograde pancreatography as superior imaging modality that detects both parenchymal and ductal changes of chronic pancreatitis at an early stage. Magnetic resonance pancreatography is a further promising diagnostic tool without the risk of pancreatitis after endoscopic retrograde pancreatography, but imaging of the side branches, which is crucial for detection of early chronic pancreatitis, is not yet sufficient. Faecal elastase is a progress in non-invasive testing of exocrine pancreatic function, but its value for the diagnosis of chronic pancreatitis under conditions of clinical practice is limited. Several (13)C breath tests have been developed, but their availability and their diagnostic accuracy in chronic pancreatitis is still limited. Light to moderate exocrine pancreatic insufficiency is not detectable with adequate accuracy by tubeless function tests. A specific serum marker of pancreatic fibrosis which would reliably indicate the presence of chronic pancreatitis or its progression to is not available.

Using breath tests wisely in a gastroenterology practice: an evidence-based review of indications and pitfalls in interpretation

Breath tests are a simple and safe alternative to more invasive investigation strategies for many gastroenterological conditions. Both the hydrogen breath tests and the new 13C stable radioisotope breath tests are nonradioactive and safe in children and pregnancy. The range of diseases that can be identified include Helicobacter pylori infection, lactose and fructose intolerance, bacterial overgrowth, bile salt wastage, pancreatic insufficiency, liver dysfunction, and abnormal small bowel transit. In this review, the physiology supporting these tests and the principles of normal gas dynamics in the gut are briefly reviewed and then related to the test preparation and interpretation in two parts: 1) detection of H. pylori and 2) small bowel, pancreatic, and hepatobiliary disorders. A MEDLINE search reviewing all English language abstracts from 1966 to March, 2001 was performed, with an additional review of abstracts from major national meetings from 1997 to 2001. Using the information from this review, the performance characteristics of the various tests were detailed, and an attempt is made to provide some literature-based guidance regarding their indications and limitations. The interpretation of "flat" breath tests and the selective use of methane collection and colonic alkalinization are discussed. Breath tests are valuable tools that are, in general, underutilized in evaluating dyspepsia and functional bloating and diarrhea, as well as suspected malabsorption, including lactose intolerance.

Pancreatic function tests: when to choose, what to use

Although techniques for high-resolution imaging of the pancreas are constantly being improved, the evaluation of pancreatic function remains crucial for the workup of pancreatic diseases. More than 20 direct and indirect tests are available for the assessment of pancreatic function. Measurement of fecal elastase-1 is recommended as the most suitable test for the initial assessment of pancreatic function. Among other techniques, the pancreolauryl test, and alternatively the BT-PABA (N-benzoyl-L-tyrosyl-p-aminobenzoic acid) or the (13)C-mixed-triglyceride test, yield the best sensitivity and specificity. Nevertheless, all indirect tests are of limited value in patients with mild to moderate impairment of pancreatic function. In these patients, the secretin-caerulein test remains the gold standard.

MR hydrometry to assess exocrine function of the pancreas: initial results of noninvasive quantification of secretion

PURPOSE

To evaluate magnetic resonance (MR) hydrometry, a method of quantifying fluid amounts by using MR imaging, for assessing the exocrine function of the pancreas after stimulation with secretin.

MATERIALS AND METHODS

Images were obtained with a single-shot turbo spin-echo sequence by using a 1.0-T magnet with a quadrature body coil. Image postprocessing and evaluation were performed at an external workstation by using a specially designed histogram algorithm that translates the MR signal intensity of duodenal filling into an actual amount of duodenal fluid. This algorithm was tested in vitro and in vivo. Finally, MR hydrometry results in five patients were correlated with those of the secretin-cerulein test.

RESULTS

The phantom measurements showed a high correlation (r = 0.99) between the actual amount of fluid in the imaging volume and the calculated results. In vivo, the ability of MR hydrometry to enable exact quantification of fluid amounts was demonstrated. In correlating the signal intensity of duodenal filling with the exact amount of additional fluid in the duodenum in volunteers, a coefficient of 0.043 gray tones per pixel per milliliter was calculated. The correlation (r) between secretin-stimulated duodenal fluid output estimated by using tube aspiration and that estimated by using MR hydrometry was 0.946 (P <.05).

CONCLUSION

MR hydrometry is a promising noninvasive method of assessing fluid output as a measure of exocrine pancreatic function.

Malabsorption testing: a review

Malabsorption syndromes often present diagnostic dilemmas to even the most experienced clinicians. Several malabsorption screening tests are available, but d-xylose testing is our initial screening method of choice. Recent innovations such as serum assays for antibodies associated with celiac sprue are improving the work-up of patients with suspected malabsorption. In addition, physicians are applying technological advances in imaging to determine the underlying pathologies responsible for the occurrence of malabsorption and maldigestion. Breath testing remains a controversial modality in the work-up of patients with malabsorption. Tubeless tests of pancreatic function are also the subject of debate due to a lack of sensitivity for diagnosing mild to moderate chronic pancreatic insufficiency. This review identifies and provides critical analysis of new developments in the field of malabsorption testing. The authors also provide a clinical algorithm for diagnosing malabsorption.

Detection of impaired intestinal absorption of long-chain fatty acids: validation studies of a novel test in a rat model of fat malabsorption

BACKGROUND

Classic fat balance studies detect fat malabsorption but do not discriminate between the potential causes of malabsorption, such as impaired intestinal lipolysis or reduced uptake of fatty acids.

OBJECTIVE

We aimed to validate a novel test for the specific, sensitive detection of impaired intestinal uptake of long-chain unesterified fatty acids in an appropriate rat model of fat malabsorption.

DESIGN

The absorption and appearance in plasma of [(13)C]palmitic acid were determined in control rats and in rats with fat malabsorption due either to chronic bile deficiency (permanent bile diversion) or to oral administration of the lipase inhibitor orlistat (200 mg/kg diet). [(13)C]Palmitic acid results were compared with the percentage absorption of ingested dietary fat determined by fat balance.

RESULTS

Between 1 and 6 h after intraduodenal administration, plasma [(13)C]palmitate concentrations in control rats were 4-10-fold higher than in bile-deficient rats (P < 0.05) but were not significantly different between orlistat-supplemented rats and their controls. In control and bile-deficient rats, plasma [(13)C]palmitate concentrations allowed complete discrimination between normal (>92%) and reduced (<92%) fat absorption, whereas the percentage absorption of [(13)C]palmitate over 48 h appeared to be highly correlated with the percentage absorption of ingested dietary fat (r = 0.89, P < 0.001).

CONCLUSIONS

The [(13)C]palmitic acid absorption test detects impaired intestinal absorption of long-chain fatty acids selectively and sensitively in a rat model of fat malabsorption due to bile deficiency. Our data strongly support the use of the [(13)C]palmitic acid absorption test for the diagnosis of clinical fat malabsorption syndromes.

13C-egg white breath test: a non-invasive test of pancreatic trypsin activity in the small intestine

BACKGROUND

The recent availability of egg white protein highly enriched with (13)C has allowed breath test technology to be adapted for the study of protein digestion and absorption. Pancreatic trypsin is considered to be the key enzyme in the proteolytic cascade.

AIM

To evaluate trypsin activity in the small intestine of healthy volunteers and patients with pancreatic disease by a recently developed (13)C-egg white breath test.

METHODS

A total of 48 healthy volunteers and 30 patients with pancreatic disease were studied after ingestion of a test meal consisting of 22 g (13)C-labelled egg protein. Breath samples were taken before and after ingestion of the meal and analysed for (13)CO(2) concentration. Moreover, pancreatic trypsin output after maximal stimulation was measured in 13 patients and nine healthy volunteers.

RESULTS

The six hour cumulative (13)CO(2) excretion in breath was significantly lower in patients than controls (mean (SEM): 6.23 (0.82)% v 19.16 (0. 58)%, p<0.0001). An excellent correlation was found between the six hour cumulative (13)CO(2) excretion and trypsin activity after maximal pancreatic stimulation.

CONCLUSION

The non-invasive (13)C-egg white breath test is promising as an indirect pancreatic proteolytic function test.

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.

13C labelled cholesteryl octanoate breath test for assessing pancreatic exocrine insufficiency

BACKGROUND

A non-invasive test for assessment of fat digestion has been developed based on the intraluminal hydrolysis of cholesteryl-[1-13C]octanoate by pancreatic esterase.

AIMS

To determine the diagnostic performance of this breath test in the assessment of exocrine pancreatic function.

METHODS

The test was performed in 20 healthy controls, 22 patients with chronic pancreatic disease (CPD), four with biliopancreatic diversion (BPD), and 32 with non-pancreatic digestive diseases (NPD); results were compared with those of other tubeless tests (faecal chymotrypsin and fluorescein dilaurate test).

RESULTS

Hourly recoveries of 13CO2 were significantly lower in CPD when compared with healthy controls or NPD. In patients with CPD with mild to moderate insufficiency, the curve of 13CO2 recovery was similar to that of healthy controls, while in those with severe insufficiency it was flat. In three patients with CPD with severe steatorrhoea, a repeat test after pancreatic enzyme supplementation showed a significant rise in 13CO2 recovery. The four BPD patients had low and delayed 13CO2 recovery. Only eight of the 32 patients with NPD had abnormal breath test results. There was a significant correlation between the results of the breath test and those of faecal chymotrypsin, the fluorescein dilaurate test, and faecal fat measurements. For the diagnosis of pancreatic disease using the three hour cumulative 13CO2 recovery test, the sensitivity was 68.2% and specificity 75.0%; values were similar to those of the other two tubeless pancreatic function tests. In seven healthy controls, nine patients with CPD, and nine with NPD a second breath test was performed using Na-[1-13C]octanoate and a pancreatic function index was calculated as the ratio of 13C recovery obtained in the two tests: at three hours this index was abnormal in eight patients with CPD and in three with NPD.

CONCLUSION

The cholesteryl-1[1-13C]octanoate breath test can be useful for the diagnosis of fat malabsorption and exocrine pancreatic insufficiency.