What biochemical tests should I consider for a patient presenting with unexplained fatigue and weight loss?

For a patient presenting with unexplained fatigue and weight loss, the following biochemical tests should be considered in primary care:

• Full blood count (FBC) urgently within 48 hours to assess for possible leukaemia or anaemia ¹.
• Serum CA125 measurement in women aged 18 and over to investigate possible ovarian cancer ¹.
• Blood glucose levels to identify new-onset diabetes, especially in patients aged 60 and over, which may indicate pancreatic cancer ¹.
• Serum protein electrophoresis or plasma viscosity/erythrocyte sedimentation rate if myeloma is suspected, particularly with bone pain or unexplained fractures ¹.
• Consider quantitative faecal immunochemical testing if iron-deficiency anaemia is present, which may suggest colorectal cancer ¹.

Additionally, an urgent chest X-ray should be offered within 2 weeks for patients aged 40 and over with unexplained fatigue and weight loss who have a history of smoking or asbestos exposure, or if respiratory symptoms are present, to exclude lung or mesothelioma ¹.