Diagnosing small bowel malabsorption: a review

Gastrointestinal failure in the ICU

PURPOSE OF REVIEW

The current review summarizes different aspects of assessment of gastrointestinal function and provides a practical approach to management of adult patients with gastrointestinal dysfunction in the ICU.

RECENT FINDINGS

Different ways to define gastrointestinal failure have been used in the past. Recently, the term 'acute gastrointestinal injury (AGI)' has been proposed to specifically describe gastrointestinal dysfunction as a part of multiple organ dysfunction syndrome. Possible pathophysiological mechanisms and different aspects in assessment of gastrointestinal function in adult ICU patients are presented. Currently, there is no single marker that could reliably describe gastrointestinal dysfunction. Therefore, monitoring and management is still based on complex assessment of different gastrointestinal symptoms and feeding intolerance, even though this approach includes a large amount of subjectivity. The possible role of biomarkers (citrulline, enterohormones, etc.) and additional parameters like intra-abdominal pressure remains to be clarified.

SUMMARY

Defining gastrointestinal failure remains challenging but broad consensus needs to be reached and disseminated soon to allow conduct of interventional studies. A systematic approach to management of gastrointestinal problems is recommended.

Testing for Chronic Diarrhea

Chronic diarrhea is a frequently encountered symptom in clinical practice. The etiologies for chronic diarrhea are diverse and broad with varying clinical implications. A useful method of categorizing chronic diarrhea to guide a diagnostic work-up is a pathophysiology-based framework. Chronic diarrhea may be categorized as malabsorptive, secretory, osmotic, and inflammatory or motility related. Frequently, overlap between categories may exist for any given diarrhea etiology and diagnostic testing must occur with an understanding of the differential diagnosis. Investigations to achieve a diagnosis for chronic diarrhea range from screening blood and stool tests to more directed testing such as diagnostic imaging, and endoscopic and histological evaluation. The pathophysiology-based framework proposed in this chapter will allow the clinician to select screening tests followed by targeted tests to minimize cost and complications to the patient, while providing a highly effective method to achieve an accurate diagnosis.

Interrelationships between glutamine and citrulline metabolism

PURPOSE OF REVIEW

This article analyzes the contribution of glutamine to the synthesis of citrulline and reviews the evidence that glutamine supplementation increases citrulline production.

RECENT FINDINGS

Glutamine supplementation has been proposed in the treatment of critically ill patients; however, a recent large multicenter randomized controlled trial resulted in increased mortality in the glutamine-supplemented group. Within this context, defining the contribution of glutamine to the production of citrulline, and thus to de-novo arginine synthesis, has become a pressing issue.

SUMMARY

The beneficial effects of glutamine supplementation may be partially mediated by the effects of glutamine on citrulline synthesis by the gut and the de-novo synthesis of arginine by the kidney and other tissues. Although there is no strong evidence to support that glutamine is a major precursor for citrulline synthesis in humans, glutamine has the potential to increase overall gut function and in this way increase citrulline production.

Disorders associated with malabsorption of iron: A critical review

Malabsorption is a disorder of the gastrointestinal tract that leads to defective digestion, absorption and transport of important nutrients across the intestinal wall. Small intestine is the major site where most of the nutrients are absorbed. There are three main mechanisms of malabsorption; premucosal, mucosal and postmucosal. Premucosal malabsorption is the inadequate digestion due to improper mixing of gastrointestinal enzymes and bile with chyme. This could be because of surgical resection of the small intestine or a congenital deficiency of the enzymes and bile responsible for digestion e.g. postgastrectomy, chronic pancreatitis, pancreatic cancer, cystic fibrosis, gallstones, cholangitis etc. Mucosal malabsorption occurs in celiac disease, tropical sprue, Crohn's disease etc. Postmucosal condition arises due to impaired nutrients transport e.g. intestinal lymphangiectasia, macroglobulinemia etc. Disorders of malabsorption lead to decreased iron absorption and produce iron deficiency anemia. Using the index terms malabsorption, postgastrectomy, chronic pancreatitis, pancreatic cancer, cystic fibrosis, gallstones, cholangitis, celiac disease, tropical sprue, Crohn's disease intestinal lymphangiectasia, macroglobulinemia and iron deficiency anemia the MEDLINE and EMBASE databases were searched. Additional data sources included bibliographies and references of identified articles.

Effect of Teduglutide, a Glucagon-like Peptide 2 Analog, on Citrulline Levels in Patients With Short Bowel Syndrome in Two Phase III Randomized Trials

Objectives:

In clinical trials, treatment with the glucagon-like peptide 2 analog teduglutide was associated with improved fluid and nutrient absorption and increased intestinal villus height and crypt depth in patients with short bowel syndrome (SBS). Plasma citrulline, an amino acid produced by enterocytes, is considered a measure of enterocyte mass. This analysis assessed changes in plasma citrulline levels in patients with SBS in 2 phase III clinical studies of teduglutide.

Methods:

Both teduglutide studies (0.05 or 0.10 mg/kg/day in CL0600-004 and 0.05 mg/kg/day in CL0600-020) were phase III, 24-week, double-blind, and placebo controlled. Plasma citrulline levels were analyzed and validated by liquid chromatography coupled to tandem mass spectrometry.

Results:

In both the CL0600-004 and CL0600-020 studies, change in mean plasma citrulline concentrations at Week 24 vs. baseline was significantly greater with teduglutide compared with placebo (10.9 (0.05-mg/kg/day dose) and 15.7 (0.10-mg/kg/day dose) vs. 2.0 μmol/L and 20.6 vs. 0.7 μmol/L, respectively, for each study (P≤0.0001 for each comparison with placebo)). Teduglutide treatment was associated with reductions from baseline in PS (parenteral support) volume requirements; however, a significant correlation between PS reduction and increase in plasma citrulline at Week 24 was observed in only one out of the three teduglutide treatment groups.

Conclusions:

In 2 phase III studies, patients receiving teduglutide had significant increases in plasma citrulline at Week 24 compared with patients receiving placebo. Increases in plasma citrulline concentrations likely reflect enterocyte mass expansion, but no clear correlation was detected between change in plasma citrulline and change in weekly PS volume.

The Microbiome, Intestinal Function, and Arginine Metabolism of Healthy Indian Women Are Different from Those of American and Jamaican Women

BACKGROUND

Indian women have slower arginine flux during pregnancy compared with American and Jamaican women. Arginine is a semi-essential amino acid that becomes essential during periods of rapid lean tissue deposition. It is synthesized only from citrulline, a nondietary amino acid produced mainly in the gut. The gut is therefore a key site of arginine and citrulline metabolism, and gut microbiota may affect their metabolism.

OBJECTIVE

The objective of this study was to identify differences in the gut microbiota of nonpregnant American, Indian, and Jamaican women and characterize the relations between the gut microbiota, gut function, and citrulline and arginine metabolism.

METHODS

Thirty healthy American, Indian, and Jamaican women (n = 10/group), aged 28.3 ± 0.8 y, were infused intravenously with [guanidino-15N2]arginine, [5,5-2H2]citrulline, and [15N2]ornithine and given oral [U-13C6]arginine in the fasting and postprandial states. Fecal bacterial communities were characterized by 16S rRNA gene sequencing.

RESULTS

In the fasting state, Indian women had lower citrulline flux than did American and Jamaican women [7.0 ± 0.4 compared with 9.1 ± 0.4 and 8.9 ± 0.2 μmol ⋅ kg fat-free mass (FFM)-1 ⋅ h-1, P = 0.01] and greater enteral arginine conversion to ornithine than did American women (1.4 ± 0.11 compared with 1.0 ± 0.08 μmol ⋅ kg FFM-1 ⋅ h-1, P = 0.04). They also had lower mannitol excretion than American and Jamaican women (154 ± 37.1 compared with 372 ± 51.8 and 410 ± 39.6 mg/6 h, P < 0.01). Three dominant stool community types characterized by increased abundances of the genera Prevotella, Bacteroides, and Bacteroides with Clostridium were identified. Indian women had increased mean relative abundances of Prevotella (42%) compared to American and Jamaican women (7% and < 1%, P = 0.03) which were associated with diet, impaired intestinal absorptive capacity, and arginine flux.

CONCLUSIONS

These findings suggest that dysregulated intestinal function and a unique gut microbiome may contribute to altered arginine metabolism in Indian women.

A novel method to identify fat malabsorption: the Serum Retinyl Palmitate Test

BACKGROUND

Malabsorptive etiologies of chronic diarrhea are important to identify. The 72-h stool for fecal fat test (FFT), the gold standard for diagnosing fat malabsorption, is fraught with limitations that impact its reliability. Vitamin A, a fat-soluble vitamin, parallels the absorption of lipids. We assessed the feasibility and validate a novel clinical test, retinyl palmitate (RP), for the diagnosis of fat malabsorption, and to compare the results to the FFT.

METHODS

Using a case-control study design, patients with chronic diarrhea secondary to suspected malabsorption, and healthy control subjects were identified. A Dietitian taught subjects to consume a 100g fat diet for the FFT with measurements of stool fat after 72-h. Serum levels of Vitamin A (retinol) and RP were measured by reversed-phase high pressure liquid chomatography. Two-way comparisons were made between the groups using 2 sample Wilcoxon rank-sum tests.

RESULTS

Sixteen patients completed this study (8 cases and 8 control subjects). Fecal fat results were available for 15/16 patients. The sensitivity of the FFT was 100% (identified all cases), but the FFT specificity was 42%, as 4/7 control patients were identified as malabsorbers. Cases with short bowel syndrome had the lowest RP levels but this did not meet statistical significance. There was no significant difference for serum RP levels when comparing cases and control patients' AUC.

CONCLUSIONS

Serum RP is useful to identify malabsorption, albeit in severe cases. Furthermore, we have shown that the 72-hour FFT has poor performance characteristics, highlighting the need for more useful diagnostics in identifying malabsorption.

Coeliac disease: an old or a new disease? History of a pathology

The celiac disease is an ancient pathology, present since the introduction of the wheat in the diet, of which the first description of the compatible clinical symptoms and signs goes back to 250 A.D. Today it is known that the expression of this pathology is multifaceted, ranging from clinical features indicative of bowel disease and malabsorption, until symptoms once unexpected, because of their extra-digestive clinical features. With our work, we wanted to retrace the history of this disease, correlating it with the intake of gluten present in wheat after cooking , ever since mankind has increased the cultivation of cereals. Re-evaluating the clinical and instrumental methods for the diagnosis of Celiac Disease, and benefitting from the most modern techniques for the morphological, biochemical and genetic study of the patients, we sought to understand whether the incidence of the disease is actually increased or if has been considered less frequent for the lower valuation of the signs once deemed more atypical, but currently considered preliminary indicative of the pathology, for its association with other autoimmune diseases, and for the study of some genetic and familiar characteristics. Each of these factors has led the modern medicine to increase epidemiological studies and expand the research potential carriers of celiac disease with safer diagnostic tests.