Evaluation of absorption function
These methods are primarily used when malabsorption syndrome is suspected, as well as to investigate the causes of chronic diarrhea.
1. D-xylose test A key test for differential diagnosis. It helps determine where the problem lies: in impaired food digestion (at the level of the stomach or intestinal lumen) or in impaired absorption of substances through the intestinal wall.
- Procedure: The patient takes 25 g of D-xylose orally. Urine is then collected for 5 hours for analysis.
- Physiological rationale: This carbohydrate is not metabolized within the body and is excreted unchanged by the kidneys. Consequently, the amount of D-xylose in the urine is a direct reflection of the volume of the substance that was successfully absorbed.
- Interpretation of results: Normally, at least 5 g of the substance should be excreted in the urine within the specified time. If this indicator is reduced, damage to the small intestinal mucosa (malabsorption) is diagnosed.
2. Assessment of vitamin B12 absorption To test absorptive capacity, vitamin B12 labeled with a radioactive isotope is used. After oral administration of the drug, its urinary excretion is evaluated.
Absorption of this vitamin can be reduced for several reasons:
- Pernicious anemia;
- Conditions following surgical intestinal resection (e.g., jejunum);
- Severe infiltrative lesions of the intestinal wall;
- Impaired intra-intestinal digestion processes;
- Severe exocrine pancreatic insufficiency.
Hematological changes (Complete Blood Count)
Pathological processes in the intestine inevitably lead to nutrient deficiencies, which is clearly reflected in the blood composition.
Anemic syndrome
- Microcytic anemia: develops as a consequence of iron deficiency. The cause can be either impaired absorption or chronic blood loss.
- Macrocytic anemia: indicates a deficiency of vitamin B12 and folic acid due to failures in their absorption.
Changes in the leukocyte differential
- Leukocytosis with neutrophilia: indicates severe inflammatory processes in the large or small intestine. It is also characteristic of bacterial intestinal infections (yersiniosis, dysentery, salmonellosis).
- Eosinophilia: serves as an important marker of eosinophilic enteritis, especially if the disease has a helminthic etiology.
Biochemical and hormonal profile
Biochemical tests allow for the assessment of the severity of malabsorption syndrome and the scale of nutrient loss.
- Trace elements and electrolytes: Prolonged diarrhea is characterized by electrolyte imbalance. A decrease in serum magnesium, calcium, and zinc concentrations directly indicates impaired absorption (found in Crohn's disease, sprue, extensive intestinal resection).
- Protein profile: In severe malabsorption, the level of total protein and individual fractions (globulins, albumins, transferrin) drops.
- Lipid metabolism: Characterized by a decrease in cholesterol levels.
- Hemostasis system: Nutrient deficiency can lead to decreased prothrombin.
Role of the hormonal profile The study of hormones (thyroxine, somatostatin, gastrin, vasoactive intestinal polypeptide, or VIP) is critically important for finding the root cause of prolonged diarrhea. Clinical correlations:
- Gastrinoma: A gastrin-secreting tumor. It may manifest exclusively as severe diarrhea and malabsorption syndrome, even in the absence of typical signs of peptic ulcer disease.
- VIPoma: A VIP-producing tumor. It presents with debilitating severe diarrhea, which, however, lacks steatorrhea.
Briefly: answers to topical questions
In which part of the intestine does the physiological absorption of vitamin B12 take place?
Physiologically, the absorption of vitamin B12 is associated with the attachment of the "B12 — intrinsic factor" complex to the ileal epithelium.
What changes in fecal analysis (coprogram) are observed in malabsorption syndrome?
In malabsorption syndrome, coprogram analysis reveals a complex of pathological signs reflecting impaired digestive capacity and nutrient absorption. The following changes are detected:
- Steatorrhea — high content of neutral fat or fatty acids.
- Amylorrhea — excess starch in the feces.
- Creatorrhea — presence of undigested muscle fibers with preserved striation.
To assess the consequences of malabsorption, remember the triad: Blood (anemia) — Proteins (decreased albumin) — Trace elements (Ca, Mg, Zn deficiency).
Class and exam questions
What is the essence of the D-xylose test and why is it needed?
This test helps differentiate the causes of digestive problems. If there is little D-xylose in the urine, it means the small intestinal mucosa is damaged and absorption itself is impaired, since the substance is not digested in the body and must be absorbed unchanged.
Why can the leukocyte differential change in intestinal diseases?
Leukocytosis with neutrophil predominance occurs in bacterial infections (salmonellosis, dysentery) and severe intestinal inflammation. Elevated eosinophils are typical for eosinophilic enteritis, often against the background of helminthic invasion.
How are hormones and chronic diarrhea connected?
Specific hormonally active tumors can stimulate intestinal secretion and motility. For example, gastrinoma or VIPoma often manifest with severe debilitating diarrhea without other classical symptoms.
What else to study on this topic
- Mechanisms of development of microcytic and macrocytic anemia in malabsorption.
- Features of the pathogenesis of eosinophilic enteritis in helminthic invasions.
- The effect of exocrine pancreatic insufficiency on vitamin B12 metabolism.
- Changes in protein and lipid metabolism in Crohn's disease and sprue.
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