Unintentional weight loss (unexplained weight loss)

Fasting laboratory tests

• FBC
• CRP
• Serum electrolytes
• Serum calcium
• Serum creatinine with eGFR
• Fasting plasma glucose
• AST
• ALT
• GGT
• Alkaline phosphatase
• TSH
• Serum albumin (severity of undernutrition)
• LDHif needednon-French guidelineWeight loss still unexplained after clinical examination: LDH is part of the initial tests proposed by the AAFP ^[2].
• Serum protein electrophoresisif needednon-French guidelineWeight loss still unexplained after clinical examination: protein electrophoresis is part of the initial tests proposed by the AAFP ^[2].
• Serum ferritinif needednon-French guidelineUnexplained weight loss, especially with anaemia: ferritin is part of the initial tests proposed by the AAFP ^[2]; unexplained iron deficiency also prompts a search for coeliac disease ^[3].
• Vitamin B12if needednon-French guidelineWeight loss still unexplained after clinical examination: the 2025 Scottish guidelines on non-specific symptoms of cancer cite vitamin B12, ferritin and folate among the useful tests, in an indicative list that is not a minimum ^[4]. The AAFP initial tests retain ferritin, without B12 or folate ^[2].
• Folateif needednon-French guidelineWeight loss still unexplained after clinical examination: the 2025 Scottish guidelines on non-specific symptoms of cancer cite vitamin B12, ferritin and folate among the useful tests, in an indicative list that is not a minimum ^[4]. The AAFP initial tests retain ferritin, without B12 or folate ^[2].
• HIV serology (if risk factor or never screened)if needednon-French guidelineRisk factor for exposure, fever, sweats, lymphadenopathy: HIV and tuberculosis are among the infectious causes of weight loss ^[2].
• Total IgAif needednon-French guidelineUnexpected weight loss, especially with digestive symptoms, fatigue or iron, B12 or folate deficiency: NICE recommends coeliac disease serology, on a gluten-containing diet for at least 6 weeks ^[3].
• IgA anti-tissue transglutaminase antibodies (tTG-IgA)if needednon-French guidelineUnexpected weight loss, especially with digestive symptoms, fatigue or iron, B12 or folate deficiency: NICE recommends coeliac disease serology, on a gluten-containing diet for at least 6 weeks ^[3].
• Total PSA (man with urinary symptoms, erectile dysfunction or haematuria)if needednon-French guidelineMan with lower urinary tract symptoms, erectile dysfunction or macroscopic haematuria: NICE proposes PSA and digital rectal examination; PSA is not linked to weight loss alone ^[5].
• CA 125 (woman aged 40 or over, if symptoms suggestive of ovarian cancer)if needednon-French guidelineWoman with unexplained weight loss, fatigue or bowel disturbance: NICE proposes considering tests for ovarian cancer; from age 40, CA 125 then pelvic ultrasound depending on the threshold; before age 40, ultrasound without CA 125 alone ^[5].

Urine tests

• Urine dipstick

Imaging

• Chest X-ray