Stool composition in factitial diarrhea: a 6-year experience with stool analysis

Using Electrolyte Free Water Balance to Rationalize and Treat Dysnatremias

Dysnatremias or abnormalities in plasma [Na+] are often termed disorders of water balance, an unclear physiologic concept often confused with changes in total fluid balance. However, most clinicians clearly recognize that hypertonic or hypotonic gains or losses alter plasma [Na+], while isotonic changes do not modify plasma [Na+]. This concept can be conceptualized as the electrolyte free water balance (EFWB), which defines the non-isotonic components of inputs and outputs to determine their effect on plasma [Na+]. EFWB is mathematically proportional to the rate of change in plasma [Na+] (dPNa/dt) and, therefore, is actively regulated to zero so that plasma [Na+] remains stable at its homeostatic set point. Dysnatremias are, therefore, disorders of EFWB and the relationship between EFWB and dPNa/dt provides a rationale for therapeutic strategies incorporating mass and volume balance. Herein, we leverage dPNa/dt as a desired rate of correction of plasma [Na+] to define a stepwise approach for the treatment of dysnatremias.

Laboratory Utilization and Analytical Validation of Fecal Electrolyte Tests

BACKGROUND

Chronic diarrhea can be categorized as fatty, watery, or inflammatory. Watery diarrhea is further divided into secretory or osmotic types and can be differentiated by measuring fecal electrolytes and osmotic gap. However, with widespread use of endoscopy, it is unclear if these measurements are being used clinically. Furthermore, because stool is not a validated specimen type for Food and Drug Administration-approved electrolyte assays, utilization is a practical concern for laboratories before analytical validation. Here, we determined the clinical utility and validated the performance characteristics of stool electrolytes on the Beckman Coulter AU680.

METHODS

Historical results and literature review were used to determine the clinically relevant ranges for stool electrolytes (Na+, Cl-, K+, phosphate, and Mg2+). Additionally, medical chart review was performed (n = 44 patients) on results to evaluate their clinical utility in chronic diarrhea work-up. Linearity, precision, and stability studies were performed on the AU680. Accuracy was evaluated by comparing results to the Roche Cobas 6000 c501.

RESULTS

For all cases, stool electrolytes and osmotic gap proved valuable in chronic diarrhea work-up. The imprecision of the assays ranged from 0% to 5.9%. All assays were found to be linear within the instrument's analytical measurement range with appropriate slopes and intercepts. The bias between the AU680 and the Roche c501 ranged from -0.48 to 2.39 (mmol/L or mg/dL). Na+, Cl-, and K+ were stable refrigerated for 5 days and up to 1 freeze-thaw cycle. Phosphate and Mg2+ were stable refrigerated for 48 h, but unstable to freeze-thaw cycles.

CONCLUSIONS

Stool osmotic gap is valuable for evaluating chronic diarrhea and can be calculated using electrolyte concentrations measured on the AU680.

Spectrum of Drug-induced Chronic Diarrhea

The evaluation of a patient with chronic diarrhea can be quite frustrating, as it is expensive and involves multiple diagnostic studies. Moreover, identification of a drug as a cause of chronic diarrhea is a challenge in patients taking multiple medications. The disease may either be associated with intestinal mucosal changes, mimicking diseases such as celiac disease, or purely functional, with no histopathologic change. Drug-induced diarrhea may or may not be associated with malabsorption of nutrients, and a clinical improvement may occur within days of discontinuation of the drug, or may take longer when associated with mucosal injury. Diarrhea in diabetics, often attributed to poor management and lack of control, may be due to oral hypoglycaemic agents. Chemotherapy can result in diffuse or segmental colitis, whereas olmesartan and a few other medications infrequently induce a disease that mimics celiac disease, but is not associated with gluten intolerance. In short, increased awareness of a drug, as a cause for diarrhea and a clear understanding of the clinical manifestations will help clinicians to solve this challenging problem. This article aims to review drug-induced diarrhea to (a) understand known pathophysiological mechanisms; (b) assess the risk associated with frequently prescribed medications, and discuss the pathogenesis; and

Fecal electrolyte testing for evaluation of unexplained diarrhea: Validation of body fluid test accuracy in the absence of a reference method

BACKGROUND

Validation of tests performed on body fluids other than blood or urine can be challenging due to the lack of a reference method to confirm accuracy. The aim of this study was to evaluate alternate assessments of accuracy that laboratories can rely on to validate body fluid tests in the absence of a reference method using the example of sodium (Na(+)), potassium (K(+)), and magnesium (Mg(2+)) testing in stool fluid.

METHODS

Validations of fecal Na(+), K(+), and Mg(2+) were performed on the Roche cobas 6000 c501 (Roche Diagnostics) using residual stool specimens submitted for clinical testing. Spiked recovery, mixing studies, and serial dilutions were performed and % recovery of each analyte was calculated to assess accuracy. Results were confirmed by comparison to a reference method (ICP-OES, PerkinElmer).

RESULTS

Mean recoveries for fecal electrolytes were Na(+) upon spiking=92%, mixing=104%, and dilution=105%; K(+) upon spiking=94%, mixing=96%, and dilution=100%; and Mg(2+) upon spiking=93%, mixing=98%, and dilution=100%. When autoanalyzer results were compared to reference ICP-OES results, Na(+) had a slope=0.94, intercept=4.1, and R(2)=0.99; K(+) had a slope=0.99, intercept=0.7, and R(2)=0.99; and Mg(2+) had a slope=0.91, intercept=-4.6, and R(2)=0.91. Calculated osmotic gap using both methods were highly correlated with slope=0.95, intercept=4.5, and R(2)=0.97. Acid pretreatment increased magnesium recovery from a subset of clinical specimens.

CONCLUSIONS

A combination of mixing, spiking, and dilution recovery experiments are an acceptable surrogate for assessing accuracy in body fluid validations in the absence of a reference method.

Laxative abuse: epidemiology, diagnosis and management

Laxatives have been used for health purposes for over 2000 years, and for much of that time abuse or misuse of laxatives has occurred. Individuals who abuse laxatives can generally be categorized as falling into one of four groups. By far the largest group is made up of individuals suffering from an eating disorder such as anorexia or bulimia nervosa. The prevalence of laxative abuse has been reported to range from approximately 10% to 60% of individuals in this group. The second group consists of individuals who are generally middle aged or older who begin using laxatives when constipated but continue to overuse them. This pattern may be promulgated on certain beliefs that daily bowel movements are necessary for good health. The third group includes individuals engaged in certain types of athletic training, including sports with set weight limits. The fourth group contains surreptitious laxative abusers who use the drugs to cause factitious diarrhoea and may have a factitious disorder. Normal bowel function consists of the absorption of nutrients, electrolytes and water from the gut. Most nutrients are absorbed in the small intestine, while the large bowel absorbs primarily water. There are several types of laxatives available, including stimulant agents, saline and osmotic products, bulking agents and surfactants. The most frequently abused group of laxatives are of the stimulant class. This may be related to the quick action of stimulants, particularly in individuals with eating disorders as they may erroneously believe that they can avoid the absorption of calories via the resulting diarrhoea. Medical problems associated with laxative abuse include electrolyte and acid/base changes that can involve the renal and cardiovascular systems and may become life threatening. The renin-aldosterone system becomes activated due to the loss of fluid, which leads to oedema and acute weight gain when the laxative is discontinued. This can result in reinforcing further laxative abuse when a patient feels bloated and has gained weight. Treatment begins with a high level of suspicion, particularly when a patient presents with alternating diarrhoea and constipation as well as other gastrointestinal complaints. Checking serum electrolytes and the acid/base status can identify individuals who may need medical stabilization and confirm the severity of the abuse. The first step in treating laxative misuse once it is identified is to determine what may be promoting the behaviour, such as an eating disorder or use based on misinformation regarding what constitutes a healthy bowel habit. The first intervention would be to stop the stimulant laxatives and replace them with fibre/osmotic supplements utilized to establish normal bowel movements. Education and further treatment may be required to maintain a healthy bowel programme. In the case of an eating disorder, referral for psychiatric treatment is essential to lessen the reliance on laxatives as a method to alter weight and shape.

Detection of polyethylene glycol-based laxatives in stool

The ability to test stool for laxatives is an important part of patient care in some clinical circumstances. Some patients take or are given laxatives surreptitiously. Additionally, failure to take prescribed laxatives may result in treatment failure in children with constipation or encopresis. Although laboratory methods have been available to identify many laxatives in the stool, tests are not available for detecting polyethylene glycol (PEG)-based laxatives. PEG-based laxatives are frequently used in the treatment of children with constipation. We developed a mass spectrometry (MS)-based analysis for detecting PEG in stool and verified the technique in an adult volunteer. We then piloted the assay on stools from children taking PEG for constipation versus children with diarrhea who were not taking PEG. Eleven subjects with diarrhea and 8 receiving PEG were enrolled. Nine of the children with diarrhea and 7 receiving PEG were evaluated by MS. All 3 subjects with PEG who had a stool osmolal gap determined had elevated gaps. Stools of all 7 subjects with PEG were positive for PEG by MS, whereas none of the 9 subjects with diarrhea had stool positive for PEG. This new MS methodology to test stool for PEG is described. It is likely to prove useful in the documentation of surreptitious PEG administration and in evaluation of PEG treatment failure.

Factitious Diarrhea Induced by Stimulant Laxatives: Accuracy of Diagnosis by a Clinical Reference Laboratory Using Thin Layer Chromatography

Background: Surreptitious ingestion of laxatives can lead to serious factitious diseases that are difficult to diagnose. Most cases involve ingestion of bisacodyl or senna. Thin layer chromatography (TLC) of urine or stool is the only commercially available test for these laxatives. Such testing is considered highly reliable, but its accuracy in clinical practice is unknown. Our aim was to evaluate the reliability of TLC laxative testing by a clinical reference laboratory in the United States.

Methods: Diarrhea was induced in healthy volunteers by ingestion of bisacodyl, senna, or a control laxative (n = 11 for each laxative group). Samples of urine and diarrheal stool were sent in blinded fashion to the clinical reference laboratory for bisacodyl and senna analysis.

Results: TLC testing for bisacodyl-induced diarrhea revealed a sensitivity of 73% and specificity of 91% when urine was tested and sensitivity and specificity of 91% and 96%, respectively, when stool was analyzed. When diarrhea was induced by senna, the TLC assay for senna failed to identify even a single urine or stool specimen as positive (zero% sensitivity).

Conclusions: Considering the expected prevalence of surreptitious laxative abuse in patients with chronic idiopathic diarrhea (2.4%–25%, depending on the clinical setting), TLC of urine or stool for bisacodyl by this reference laboratory would often produce misleading results, and testing for senna would have no clinical value. The major problems are false-positive tests for bisacodyl and false-negative tests for senna.

Factitious diarrhea masquerading as refractory celiac disease

A 23-year-old female with a history of a histologically confirmed diagnosis of celiac disease was referred to our institution for refractory celiac disease for consideration of immunosuppressive therapy. Full workup revealed an elevated fecal magnesium level, and a concurrent diagnosis of laxative abuse was confirmed after discussion with the family. This case highlights the importance of considering factitious diarrhea in all patients admitted for refractory diarrhea, even those with documented underlying conditions.

Modulation of electroneutral Na transport in sheep rumen epithelium by luminal ammonia

Ammonia is an abundant fermentation product in the forestomachs of ruminants and the intestine of other species. Uptake as NH3 or NH4+ should modulate cytosolic pH and sodium-proton exchange via Na+/H+ exchanger (NHE). Transport rates of Na+, NH4+, and NH3 across the isolated rumen epithelium were studied at various luminal ammonia concentrations and pH values using the Ussing chamber method. The patch-clamp technique was used to identify an uptake route for NH4+. The data show that luminal ammonia inhibits electroneutral Na transport at pH 7.4 and abolishes it at 30 mM (P < 0.05). In contrast, at pH 6.4, ammonia stimulates Na transport (P < 0.05). Flux data reveal that at pH 6.4, approximately 70% of ammonia is absorbed in the form of NH4+, whereas at pH 7.4, uptake of NH3 exceeds that of NH4+ by a factor of approximately four. The patch-clamp data show a quinidine-sensitive permeability for NH4+ and K+ but not Na+. Conductance was 135 +/- 12 pS in symmetrical NH(4)Cl solution (130 mM). Permeability was modulated by the concentration of permeant ions, with P(K) > P(NH4) at high and P(NH4) > P(K) at lower external concentrations. Joint application of both ions led to anomalous mole fraction effects. In conclusion, the luminal pH determines the predominant form of ammonia absorption from the rumen and the effect of ammonia on electroneutral Na transport. Protons that enter the cytosol through potassium channels in the form of NH4+ stimulate and nonionic diffusion of NH3 blocks NHE, thus contributing to sodium transport and regulation of pH.

Surreptitious abuse of magnesium laxatives as a cause of chronic diarrhoea

Surreptitious laxative abuse is increasingly considered as a possible cause of unexplained chronic diarrhoea. Laboratory services for detection of colonic stimulant laxatives are widely available; however, laboratory facilities for identifying patients with magnesium-induced diarrhoea are not commonly provided, making diagnosis difficult. We describe three patients who surreptitiously abused magnesium laxatives, and whose diagnoses were delayed, leading in each case to extensive investigations and lengthy in-patient stays. In all three cases, the diagnosis was eventually made by the simple measurement of magnesium in a random faecal sample. We would like to increase the awareness of surreptitious magnesium laxative abuse as a cause of chronic diarrhoea so that costly and unnecessary investigations may be minimized.

Rapid gastric emptying in patients with functional diarrhea

OBJECTIVE

To analyze our experience in patients with chronic diarrhea by using a noninvasive transit study that measures gastric emptying as well as small bowel and colonic transit.

MATERIAL AND METHODS

Results from 94 consecutive transit tests, for which diarrhea was the main indication, were reviewed and correlated with the final classification of patients as having an organic or nonorganic disorder.

RESULTS

Sixty patients were considered to have a nonorganic cause of diarrhea, of whom 15 had previously undergone cholecystectomy. The other 34 patients were considered to have diarrhea on the basis of an organic diagnosis. Gastric emptying was more often rapid in patients with a nonorganic cause (P < 0.05), but not if cholecystectomy had been performed previously. Small bowel transit was fast more often in patients with organic diarrhea than in those with no organic cause of the diarrhea (P < 0.05); colonic transits showed no significant differences among groups.

CONCLUSION

The findings implicate a motor abnormality of the upper gut, rapid gastric emptying, as a pathophysiologic mechanism of functional bowel disorders with diarrhea. The results imply that additional prospective observations should be worth-while.