# Underweight - Category: chronic - Review status: reviewed (every claim checked against a document named on this page) - Sources: ICPC-3 (WONCA International Classification of Primary Care, 3rd edition) class TS50 - condition scope only, no dose · Irritable Bowel Syndrome - StatPearls - NCBI Bookshelf - https://www.ncbi.nlm.nih.gov/books/NBK534810/ · No dose - referral pathway, no medicine given in primary care - Verified date: 2026-08 ## Verified against - No dose - referral pathway, no medicine given in primary care ## Treatment metadata - No drug therapy in primary care (Recognition & Referral) ## Complete treatment card ```text UNDERWEIGHT Sources: ICPC-3 (WONCA International Classification of Primary Care, 3rd edition) class TS50 - condition scope only, no dose · Irritable Bowel Syndrome - StatPearls - NCBI Bookshelf - https://www.ncbi.nlm.nih.gov/books/NBK534810/ · No dose - referral pathway, no medicine given in primary care Review status: REVIEWED against the source listed above (2026-08) IS IT THIS? - reference only, to read alongside your own examination SYMPTOMS - what the patient reports (5) - The story is weight loss the patient never intended, poor appetite and feeling full early [poor appetite · weight loss] - Weight keeps falling even when intake looks adequate or has gone up - Tiredness, falling physical function, less exercise capacity and trouble with daily activities [fatigue] - Part of that tiredness is anaemia from the underlying chronic illness [anaemia · fatigue] - It arrives late in cancer or another chronic disease, so the history usually confirms a suspicion already held SIGNS - what you find (4) - Marked muscle wasting, especially in the limbs, giving a gaunt look and a weak grip [muscle wasting] - Less fat under the skin, with shoulders, collarbones, ribs, hips and cheeks standing out - BMI is low, typically under 20 kg/m2 - Look for pallor, swelling or enlarged organs from the illness underneath [pallor] TESTS (10) - The definition is unintended weight loss over 5%, or a BMI under 20 kg/m2, alongside continuing muscle loss, fatigue, poor appetite and declining function - Work out baseline calorie and protein intake and the needs on top, allowing for raised resting energy use - Bioelectrical impedance or DEXA quantifies muscle mass and fat stores and tracks change - Grip strength below 20 kg in men or below 14 kg in women shows impaired muscle function and predicts poor outcomes - Albumin, prealbumin and transferrin gauge protein status and nutritional reserve - A raised CRP points to inflammation driving the wasting, and tracks with how bad it is - A full blood count picks up anaemia and may hint at inflammation or infection - Electrolytes with liver and kidney function show malnutrition and organ damage - Check testosterone and thyroid hormones, which can worsen weight loss, wasting and fatigue - Look for deficiency of iron, vitamin D, B12 and folate, all common in chronic disease IF NOT THIS - what else fits (7) - Anorexia nervosa and other eating disorders lose weight severely but without the muscle wasting or metabolic changes - Plain starvation from too little food strips fat and lean mass without inflammation, and recovers with feeding - Heart failure, kidney failure, cancer and COPD cause malnutrition without the inflammatory pattern, though they can progress into it - Sarcopenia is age-related muscle loss with functional decline, but without inflammation or big weight loss - Most who are cachectic are also sarcopenic, but most with sarcopenia are not cachectic - Endocrine disease, malabsorption and psychiatric disorders also belong here - History, examination and relevant blood tests usually separate them Source StatPearls "Anorexia and Cachexia" - disease-level clinical article Status traced to the source above 1. NO DRUG THERAPY IN PRIMARY CARE (RECOGNITION & REFERRAL)[1st line] Adult A nonspecific finding; the GP's task is to identify and treat the underlying cause (malnutrition, chronic disease, eating disorder, overactive thyroid) rather than prescribe for being underweight itself. - Refer Peds Children follow the same pathway: recognise and refer. No primary-care medicine is implied. Source No dose - referral pathway, no medicine given in primary care Why A nonspecific finding; the GP's task is to identify and treat the underlying cause (malnutrition, chronic disease, eating disorder, overactive thyroid) rather than prescribe for being underweight itself. Caution Unintentional significant weight loss can be a red flag for malignancy, tuberculosis, or other serious systemic illness and needs work-up. No medicine is prescribed for this in primary care - this entry is for recognition and referral. Anything given is decided by the service it is referred to. Prices are indicative (dataset snapshot 2026-06); verify with the pharmacy. ``` --- Dawaa Reference is a reference for prescribers, not a medical device, and does not replace clinical judgement. [Privacy policy](/privacy)