• Clinical science

Malabsorption

Abstract

Despite the distinct underlying pathological mechanisms of malabsorption and maldigestion, the term malabsorption is used to refer to both disorders in clinical practice. Malabsorption (e.g., celiac disease, lactose intolerance) describes a malfunction of the intestinal wall, resulting in the insufficient absorption of breakdown products. Maldigestion (e.g., exocrine pancreas insufficiency or cholestasis) is caused by an intraluminal disorder (insufficient secretion of pancreatic enzymes or bile), which prevents the adequate breakdown of food in the intestinal lumen. Both disorders can lead to malnourishment, which, in children, may manifest with delayed and inadequate physical development. Adults mainly present with chronic diarrhea, weight loss, and signs of malnutrition (e.g., iron deficiency anemia). Diagnostic tests assess the digestion of individual food components. Management focuses on the underlying disease; e.g., patients with celiac disease should adhere to a gluten-free diet.

Definition

Malabsorption disorders can be caused by either the insufficient absorption or digestion of nutrients. The condition can be further defined as global or partial.

Etiology

Maldigestion

Impaired breakdown of food in the intestinal lumen

Malabsorption

Impaired absorption of digested food caused by alterations of the intestinal mucosa

References:[1][2][3][4]

Clinical features

General symptoms

  • Global malabsorption
    • Diarrhea (most common), steatorrhea, abdominal distension, flatulence
    • Weight loss, fatigue
    • Additional symptoms of specific deficiencies
  • Partial (isolated) malabsorption: only symptoms specific to individual nutrient deficiencies (e.g., impaired cobalamin absorption with megaloblastic anemia)

Fat-soluble vitamin deficiencies

Vitamins Symptoms Causes Sources

Vitamin A

  • Night blindness
  • Retinopathy
  • Xerophthalmia
  • Xeroderma
Vitamin D
  • Lack of sun exposure
  • Kidney or liver disease
  • Inadequate intake, fat malabsorption
Vitamin E
  • Insufficient intake, fat malabsorption
  • Meat, eggs, oils, leafy vegetables

Vitamin K
  • Liver failure
  • Fat malabsorption
  • Green vegetables, broccoli, spinach

The fat cat is in the ADEK (pronounced “attic”)

Water-soluble vitamin deficiencies

Vitamins Clinical features Causes Sources

Vitamin B1

(Thiamine)

  • Chronic alcohol consumption
  • Malnutrition, starvation
  • Diarrhea, prolonged vomiting
  • Diuretics, dialysis
  • Bariatric surgery
  • Yeast, pork, whole grain rice (unpolished), cereals, legumes
Vitamin B2 (Riboflavin)
  • Meat, fish, eggs, milk, green vegetables, yeast

Vitamin B3

(Niacin)

  • Meat (liver), cereals, seeds, legumes

Vitamin B5

(Pantothenic acid)

  • Insufficient intake

Vitamin B6

(Pyridoxine)

  • Meat, nuts, whole grains, vegetables

Vitamin B12

(Cobalamin)

  • Megaloblastic anemia: mostly asymptomatic; possibly symptoms of weakness and cardiopulmonary impairment
  • Neurologic symptoms
  • Meat and dairy products
Vitamin C (Ascorbic acid)
  • Prolonged insufficient intake
  • Citrus fruits, strawberries, tomatoes, potatoes, cabbage, spinach

Folic acid

(Folate)

  • Megaloblastic anemia: mostly asymptomatic; possibly symptoms of weakness and cardiopulmonary impairment
  • Glossitis
  • Most common vitamin deficiency in the US
  • Green leaves

Other deficiencies

References:[1][2][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][9]

Diagnostics

  • Blood tests: macrocytic and/or microcytic anemia; ↓ electrolytes, ↓ total protein, vitamin deficiencies
  • Stool tests
    • Analysis of fecal fat over 72 hours > 7 g/24 h is considered pathological
    • Detection of pathogens
  • D-xylose absorption test: assesses the absorptive function of the upper small intestine
    • Overnight fast → collection of urine for 5 hours following oral administration of 25 g xylose → if urine xylose levels < 4 g/5 h, diagnostic for malabsorptive disorders with damage to the intestinal mucosa (e.g., celiac disease, Whipple's disease)
    • Collection of a venous blood sample after one hour → levels < 20 mg/dL of serum D-xylose are pathological
  • Hydrogen breath test: assess the intestinal absorption of individual carbohydrates
  • Further testing for underlying diseases: e.g., celiac disease or lactose intolerance

References:[1][2][20]

Differential diagnoses

Protein-losing enteropathy

  • Etiology
  • Clinical features: hypoalbuminemia with peripheral edema
    • In cases of systemic diseases, symptoms may be those of the underlying condition.
    • Further gastrointestinal symptoms may occur depending on the underlying disorder.
  • Treatment
    • Treatment of the underlying disease

The differential diagnoses listed here are not exhaustive.

Treatment

  • Symptomatic treatment
    • Oral supplementation of fluid, nutrients, and vitamins
    • Calorie and protein-enriched diet
    • IV nutrition in severe cases (e.g., following extensive intestinal resection)
  • Causal treatment of the underlying disease

References:[2]