Weight Loss

Differential Diagnosis

Common Diagnoses

Occasional Diagnoses

Rare Diagnoses

  • Any Chronic Infection (Especially Tuberculosis)
  • Endocrine: Addison’s Disease, Phaeochromocytoma
  • AIDS
  • Malnutrition (Rare in Developed Countries, Common Worldwide)

Ready Reckoner

Key distinguishing features of the most common diagnoses

Normal StressDepressionEating DisordersHyperthyroidismMalignancy
Mild AnxietyYes PossibleNoNoNo
Loss of Appetite PossibleYesNoNoYes
Distorted Body ImageNoNoYesNoNo
Recurrent ProblemYes Possible Possible PossibleNo
Severe MalaiseNoYes Possible PossibleYes

Possible Investigations

Likely:Urinalysis, FBC, ESR/CRP, TFT, U&E, LFT, CXR, blood glucose or HbA1c.

Possible:Autoimmune screen, HIV test, CA-125, bowel investigations such as FIT, faecal calprotectin or antiendomysial and anti-gliadin antibodies, other hospital-based investigations.

Small Print:None.

  • Urinalysis: For possible undiagnosed diabetes; proteinuria in renal failure.
  • FBC and ESR/CRP: Hb may be reduced and ESR/CRP elevated in malignancy and any chronic disorder. Raised platelets associated with oesophageal or stomach cancer.
  • U&E: Abnormal in renal failure and sometimes in eating disorders; sodium reduced, potassium and urea elevated in Addison’s disease.
  • TFT: Will confirm hyperthyroidism.
  • LFT: Deranged in alcoholism and liver disease.
  • Blood glucose or HbA1c: To confirm diabetes.
  • Autoimmune screen: May be helpful in suspected connective tissue disorder.
  • HIV test: If AIDS suspected.
  • CA-125: If ovarian cancer is a possibility.
  • Bowel investigations such as FIT, faecal calprotectin or anti-endomysial and anti-gliadin antibodies: If carcinoma, IBD or coeliac disease suspected.
  • CXR: May reveal carcinoma, TB, lymphadenopathy or cardiac failure.
  • Other investigations (usually hospital-based) may be required according to the symptoms accompanying the weight loss and the results of preliminary investigations.

Top Tips

  • Weight loss needs to be taken seriously but can be complex and time-consuming to assess. If presented as a ‘by the way’ at the end of a consultation for some other matter, it is reasonable to reverse the normal approach by arranging basic blood tests and urinalysis first, and booking a follow-up appointment, with the results, for a more complete assessment.
  • Establish whether episodes of weight loss have happened before. Patients, or their records, may indicate, for example, that they always lose weight when stressed.
  • Check that the patient really has lost weight. The history may not be clear, and there is often a record available (e.g. new patient check or health promotion data) of previous weight.
  • Look at the patient. The obviously cachectic will have significant disease and require urgent and thorough investigation.

Red Flags

  • Rapid weight loss with malaise and respiratory or gastrointestinal symptoms strongly suggest a physical cause.
  • Think of eating disorders in young females – look for acid dental erosion on palatal surfaces of upper teeth as a giveaway sign of recurrent vomiting.
  • Weight loss in a child is caused either by significant organic pathology or emotional abuse. Look out for signs of non-accidental injury (NAI) during physical examination.
  • Depression with weight loss is a difficult problem; it may be the primary cause or the change in mood may be secondary to some physical illness. Either way, don’t overlook significant depression while you arrange investigations; there is nothing to be lost in starting antidepressants while you continue to exclude a physical cause, so long as you explain your strategy to the patient.

Published: 2nd August 2022 Updated: 10th April 2024

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