When taking a medical history it is routine to ask about a patient's weight. Weight loss is a non-specific symptom with wide-ranging differential diagnoses. Depression commonly underlies weight loss but it is essential to exclude organic causes.

Red flag symptoms

Fever

Night sweats

Rapid loss of weight

Respiratory symptoms

Bone pain

Polyuria and polydipsia

Dysphagia

Low mood

An unintentional loss of more than 5 per cent of a patient's usual body weight is significant and may indicate serious underlying pathology.

Assess how quickly the patient has lost weight and enquire about appetite. The more rapid the weight loss the more likely it is to result from organic disease.

Where the patient reports a good food intake, endocrine causes such as diabetes mellitus or thyrotoxicosis must be considered.

A significantly reduced appetite will clearly result in weight loss and may be due to GI symptoms, such as vomiting or dysphagia, or be a feature of clinical depression.

In the majority of clinical scenarios, patients report a normal or slightly reduced appetite. The line of enquiry should be made according to any other accompanying symptoms.

A review of symptoms inc-luding evaluation of possible psychological causes will assist in identifying the aetiology. It is also important to bear in mind that a patient may have underlying depression in addition to a physical illness. Drugs can suppress appetite so a medication review can be helpful, particularly in elderly patients.

Measure the patient's BMI and compare this to previous measurements, if available, to formally ascertain the extent of the weight loss.

A general physical examination should be undertaken, in particular looking for respiratory or abdominal signs of malignancy or infection. Check for signs of endocrine causes such as a goitre and skin pigmentation. If dementia is suspected, a mental state examination would be appropriate.

Investigations may include an FBC to check for infection, malignancy and chronic disease, TFTs for thyrotoxicosis and blood glucose for diabetes.

Consider inflammatory markers to look for evidence of infection or malignancy, such as a raised ESR in lymphoma. LFTs and bone profile may reveal metastases.

A chest X-ray should also be requested if infection, especially TB, or malignancy is suspected. Further investigations may include HIV serology, cortisol measurement, an autoimmune screen and GI endoscopy.