Investigations are unnecessary in many of the common regional musculoskeletal problems and osteoarthritis (OA); the diagnosis is clear from the history and examination findings. Tests help to exclude another condition and to reassure the patient or their primary care physician.

Useful blood screening tests

• Full blood count
• Haemoglobin. Normochromic, normocytic anaemia occurs in chronic inflammatory and autoimmune diseases. Hypochromic, microcytic anaemia indicates iron deficiency, often due to non-steroidal anti-inflammatory drug (NSAID) induced gastrointestinal bleeding.
• White cell count. Neutrophilia is seen in bacterial infection (e.g. septic arthritis). It also occurs with corticosteroid treatment. Lymphopenia occurs with viral illnesses or active systemic lupus erythematosus (SLE). Neutropenia may reflect drug-induced bone marrow suppression. Eosinophilia is seen in the Churg-Strauss syndrome.
• Platelets. Thrombocythaemia occurs with chronic inflammation. Thrombocytopenia is seen in drug-induced bone marrow suppression.
• Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP). An increase reflects inflammation. Plasma viscosity is also raised in inflammatory disease and measured in some laboratories in place of the sedimentation rate.
• Bone and liver biochemistry. A raised serum alkaline phosphatase may indicate liver or bone disease. A rise in liver enzymes is seen with drug-induced toxicity. For other investigations of bone, .

Other blood and urine tests:

• Protein electrophoretic strip and urinary Bence Jones protein – to exclude myeloma as a cause of a raised ESR.
• Serum uric acid – for gout.
• Antistreptolysin-O titre – in rheumatic fever.

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