Protein-losing enteropathy

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Albumin concentration reflects synthesis, distribution, catabolism and loss. In protein-losing enteropathy, albumin and other plasma proteins cross an abnormal mucosal surface or leak through dilated lymphatics into the lumen. Erosive causes include inflammatory bowel disease, ulcerative malignancy and infection. Non-erosive permeability disorders include coeliac disease, hypertrophic gastropathy and selected immune or infiltrative conditions. Lymphatic causes include primary intestinal lymphangiectasia and secondary congestion from right-sided heart disease, constrictive pericarditis, portal or mesenteric obstruction and complex congenital heart circulation. Identifying the mechanism matters because nutritional support alone rarely produces durable correction.

The diagnosis is most credible when substantial hypoalbuminaemia persists, renal and hepatic explanations have been assessed, gastrointestinal loss is demonstrated and a compatible cause is found. Faecal alpha-1-antitrypsin is relatively resistant to intestinal degradation and can be measured in stool or as clearance using paired serum and timed faecal collection according to the referral laboratory. Endoscopy may show erosions, enlarged gastric folds, white-tipped villi or apparently normal mucosa, so biopsies remain important. Severe oedema does not guarantee intravascular abundance; haemodynamic, renal and electrolyte review must guide diuretics, albumin and nutrition.

Key points

Protein-losing enteropathy describes excessive loss of plasma proteins into the gastrointestinal tract; it is a mechanism requiring an underlying diagnosis, not a final disease label.
Before attributing hypoalbuminaemia to the gut, assess hepatic synthesis, urinary protein loss, inflammation, malnutrition, burns and dilution because these are commoner explanations.
Mechanisms include erosive mucosal disease, non-erosive mucosal permeability and obstructed or high-pressure intestinal lymphatic drainage; several can coexist.
Oedema, ascites or effusions may dominate, while diarrhoea can be absent; lymphocyte and immunoglobulin loss is particularly suggestive of intestinal lymphangiectasia.
Faecal alpha-1-antitrypsin testing supports gastrointestinal protein loss, but collection, stool consistency, gastric acidity and laboratory method affect interpretation and a negative result does not always exclude it.
Endoscopy with biopsies, small-bowel imaging and cardiovascular assessment are selected from the suspected mechanism rather than ordered as an indiscriminate panel.
Treat the cause and replace nutritional deficits; high-protein or modified-fat strategies need specialist dietetic supervision, especially when lymphatic disease or intestinal failure is possible.
Albumin infusion and diuresis may temporarily manage severe fluid consequences but do not stop enteric loss and can create intravascular depletion without close monitoring.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Erosive mucosal disease

IBD, ulcerative infection and gastrointestinal malignancy allow plasma proteins to leak directly across disrupted intestinal or gastric mucosa.

Non-erosive permeability disease

Coeliac disease, hypertrophic gastropathy and other diffuse mucosal disorders increase protein passage without gross ulceration across an intact-looking surface.

Lymphatic or venous hypertension

Primary intestinal lymphangiectasia, cardiac congestion and lymphatic obstruction rupture or distend lacteals, leaking protein-rich lymph into the bowel.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Excess gastrointestinal protein loss
Albumin, immunoglobulins and other plasma proteins cross damaged mucosa or leaking lymphatics faster than hepatic synthesis can replace them.
2
Reduced plasma oncotic pressure
Falling albumin permits fluid to leave the vascular compartment, producing peripheral oedema, ascites and pleural effusions.
3
Lymphocyte and nutrient depletion
Lymphatic loss removes lymphocytes, fat and fat-soluble vitamins, compounding immune dysfunction and malnutrition in lymphangiectatic disease.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

Low oncotic pressure

Dependent oedema, ascites, pleural effusions and weight gain can occur despite muscle wasting; postural symptoms or renal impairment may reveal simultaneous intravascular depletion.

Mucosal inflammatory phenotype

Diarrhoea, pain, bleeding, fever, raised inflammatory markers or iron deficiency points towards erosive intestinal inflammation, infection or malignancy as the protein-loss surface.

Lymphatic phenotype

Oedema with lymphopenia, low immunoglobulins, steatorrhoea and fat-soluble vitamin deficiency suggests enteric lymph loss, whether primary or driven by venous congestion.

Gastric source

Epigastric symptoms, anaemia, early satiety or markedly enlarged gastric folds can indicate hypertrophic gastropathy or infiltrative disease and requires targeted gastroscopy with adequate biopsies.

Cardiovascular clue

Raised venous pressure, hepatomegaly, pericardial signs, congenital cardiac history or disproportionate right-sided failure can obstruct intestinal lymph drainage and drive protein loss.

Compromised nutrition and immunity

Loss of muscle, poor wound healing, recurrent infection, bruising, micronutrient symptoms and reduced vaccine response can reflect prolonged protein, lymphocyte and immunoglobulin depletion.

Red flags requiring action

Hypotension, acute kidney injury, oliguria or severe electrolyte disturbance in an oedematous patient suggests reduced effective circulating volume and needs urgent monitored management.
Sepsis, peritonism, gastrointestinal bleeding, obstruction or severe abdominal pain requires emergency assessment for an inflammatory, ischaemic, malignant or surgical cause.
Rapidly progressive anasarca, respiratory compromise from effusions or thrombosis risk during profound protein depletion warrants inpatient multidisciplinary care.
A child or adult with congenital heart palliation and new oedema, diarrhoea or low albumin needs prompt specialist cardiac assessment because haemodynamic failure may be central.
Do not commence prolonged parenteral nutrition or repeated albumin infusions without nutrition-team and cause-specific review.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Serum albumin and total proteinFirst step
Why
Confirm severity and follow the biochemical trajectory.
Interpretation and limitations
Interpret with C-reactive protein, hydration and liver tests because albumin falls during inflammation and dilution as well as through enteric loss.
02
Urine albumin-to-creatinine or protein-to-creatinine ratio
Why
Exclude clinically important renal protein loss efficiently.
Interpretation and limitations
Substantial proteinuria redirects evaluation towards kidney disease; a normal dipstick alone may miss non-albumin proteins and should not replace quantified testing when suspicion remains.
03
Faecal alpha-1-antitrypsin or clearance
Why
Demonstrate abnormal loss of a plasma-derived protein through the gut.
Interpretation and limitations
Use the local laboratory collection protocol and paired serum when clearance is requested; diarrhoea alters clearance and a negative result does not absolutely exclude intermittent or gastric loss.
04
Full nutritional and immune profile
Why
Define consequences and replacement needs before intervention.
Interpretation and limitations
Assess blood count, iron indices, folate, vitamin B12, calcium, magnesium, phosphate, fat-soluble vitamins, immunoglobulins and lymphocytes according to phenotype and duration.
05
Endoscopy with systematic biopsies
Why
Identify erosive, hypertrophic, coeliac, infiltrative or lymphatic mucosal disease.
Interpretation and limitations
Sample abnormal and apparently normal tissue from the anatomically plausible sites; superficial gastric biopsies may be inadequate for markedly thickened folds.
06
CT or MR enterography
Why
Assess small-bowel wall, lymphatics, mesentery, obstruction and disease beyond endoscopic reach.
Interpretation and limitations
Relate mural inflammation, mass, dilated lymphatics or venous obstruction to endoscopy and cardiac findings; capsule endoscopy is avoided when stricturing risk is unresolved.
07
Echocardiography and venous-pressure assessment
Why
Seek right-sided cardiac or pericardial drivers of lymphatic congestion.
Interpretation and limitations
Routine echocardiography may not resolve constriction or complex congenital haemodynamics, so refer for advanced cardiac imaging or catheter assessment when clinical discordance persists.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Cirrhosis

Impaired hepatic synthesis, portal signs and chronic liver imaging explain hypoalbuminaemia without proving intestinal loss, although both mechanisms can coexist.

Nephrotic syndrome

Heavy urinary protein loss, oedema and renal findings identify a renal source that should be excluded before specialist stool testing.

Inflammation or malnutrition

Raised inflammatory markers, low intake and sarcopenia reduce albumin through redistribution and inadequate substrate rather than excessive gut loss alone.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01CONFIRMEstablish true gastrointestinal protein lossFirst stepPersistent hypoalbuminaemia, oedema or effusions lack a sufficient hepatic, renal or nutritional explanation.

1Confirm the trend and review inflammation, liver synthetic function, quantified urine protein, diet, fluid state, burns and medication or infusion history.
2Request faecal alpha-1-antitrypsin testing through the local referral laboratory, following its sampling and paired-serum requirements exactly.
3Assess nutritional, immune and electrolyte consequences while documenting stool frequency, bleeding, pain, surgery, cardiac history and systemic symptoms.
4Treat immediate fluid, infection and nutrition threats without allowing temporary biochemical improvement after albumin to be mistaken for diagnostic proof.

02LOCALISEFind the responsible mechanismEnteric loss is supported or clinical suspicion remains high despite an imperfect faecal test.

1Classify the working mechanism as erosive mucosal, non-erosive permeability or lymphatic and venous congestion using symptoms and blood-pattern clues.
2Use gastroscopy, ileocolonoscopy and histology for plausible mucosal disease, ensuring coeliac and hypertrophic gastric pathology are sampled appropriately.
3Add enterography, targeted infection tests and malignancy assessment when small-bowel or systemic disease remains possible, avoiding capsule use before patency is considered.
4Investigate cardiac, portal and mesenteric pressure when oedema, lymphopenia or congenital heart history suggests secondary lymphangiectasia.

03RESTORETreat cause and nutritional consequencesA compatible cause and pattern of protein loss have been identified or severe depletion needs support during investigation.

1Treat the underlying inflammatory, infectious, malignant, gastric, lymphatic or cardiovascular disease through the appropriate specialist team.
2Create a dietitian-led energy and high-quality protein plan, considering modified long-chain fat and medium-chain triglycerides for lymphatic disease when appropriate.
3Replace documented vitamins, minerals and trace elements, and choose oral, enteral or parenteral support according to intestinal function and NICE nutrition principles.
4Use diuretics or albumin only for selected symptomatic fluid problems with weight, renal, electrolyte and haemodynamic monitoring while loss continues.

Key medicines and prescribing safety3 treatments · regimens, roles and cautions

Replenishes protein and energy while definitive treatment reduces gastrointestinal loss.

Dietary protein and energy support

Individualised dietitian-led intake targets adjusted for ongoing losses and tolerance.

Refeeding risk, renal or hepatic disease, fat malabsorption and food restriction require specialist planning; excessive protein does not correct untreated lymphatic or mucosal disease.

Provides temporary oncotic and intravascular support in selected severe decompensation or procedure settings.

Human albumin solution

Reserved specialist intravenous replacement linked to clinical indication and haemodynamic review.

Effect is transient while enteric loss continues; pulmonary oedema, fluid redistribution and sodium load are possible, particularly with cardiac or renal dysfunction.

Relieves selected symptomatic peripheral oedema, ascites or effusion while causal therapy proceeds.

Loop diuretic

Lowest effective individualised regimen with frequent renal and electrolyte reassessment.

Profound hypoalbuminaemia may reduce response, and aggressive diuresis can worsen intravascular depletion, kidney injury, hypotension and electrolyte loss despite visible oedema.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Oedema and serous effusions

Severe hypoalbuminaemia causes leg swelling, ascites and pleural fluid, impairing mobility, skin integrity and breathing in advanced disease.

Infection susceptibility

Loss of immunoglobulins and lymphocytes can impair immune defence, particularly when the underlying disease or treatment also suppresses immunity.

Malnutrition and micronutrient deficiency

Concurrent fat, vitamin and protein loss causes weight loss, weakness, bone disease and reduced tolerance of definitive treatment.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

Trend weight, oedema, abdominal girth, fluid balance, blood pressure and renal function rather than using serum albumin as the only response marker.
Repeat albumin, total protein, electrolytes, inflammatory markers and disease-specific tests at intervals determined by severity and the treatment mechanism.
Review dietary intake, muscle function, micronutrient replacement and gastrointestinal tolerance with a specialist dietitian, particularly after any restrictive fat plan.
For lymphatic loss, follow lymphocyte count, immunoglobulins and infection burden when clinically relevant and seek immunology advice before replacement decisions.
Reassess the diagnosis when biochemical loss persists despite apparently controlled disease, considering missed cardiac congestion, ongoing inflammation or incorrect collection.
Escalate to an intestinal-failure or specialist nutrition service when enteral intake cannot maintain hydration, protein-energy status or micronutrient balance.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Oedema can hide depletion

Low oncotic pressure moves fluid out of the circulation. A visibly fluid-overloaded patient may still be posturally hypotensive or develop kidney injury with rapid diuresis.

Protein loss is non-selective

Albumin draws attention, but immunoglobulins, lymphocytes, carrier proteins and coagulation-related proteins may also be lost and explain unusual complications.

A positive test needs a cause

Faecal alpha-1-antitrypsin establishes a route of loss, not its anatomy. Endoscopic, imaging and cardiovascular correlation remains necessary.

Lymphatic diets have physiology

Reducing long-chain fat can reduce intestinal lymph flow, while medium-chain triglycerides are absorbed differently; the approach risks energy and essential-fat deficits without dietetic support.

Albumin is not durable therapy

A post-infusion rise may be brief because the same loss pathway remains active. Use clinical benefit and causal control rather than chasing a laboratory number.

11Common pitfallsFrequent interpretation and management errors.

01
Diagnosing protein-losing enteropathy from hypoalbuminaemia alone without quantifying urinary protein or reviewing liver synthesis and inflammation.
02
Treating a negative faecal alpha-1-antitrypsin result as absolute exclusion despite intermittent loss, gastric degradation or collection problems.
03
Giving repeated albumin and diuretic cycles without identifying the mucosal, lymphatic or cardiovascular driver.
04
Ordering capsule endoscopy before considering a small-bowel stricture or obstruction risk.
05
Prescribing a highly restrictive low-fat diet without replacing energy, essential fatty acids and fat-soluble vitamins.
06
Assuming diarrhoea must be present and missing protein loss in a patient presenting mainly with oedema or effusions.