Top Tips for Investigations

Laboratory tests are used to support or exclude potential diagnoses. They can also be used to monitor progress, response to treatment or adverse side effects of medication. In the context of red flags for infection or malignancy, investigations are required and need to be interpreted in the clinical context.

Normal values vary with age and reference ranges are available for interpretation.

If inflammatory arthritis is suspected, investigations are often unhelpful as blood tests and radiographs can be normal at presentation. Refer early to paediatric rheumatology if there is clinical concern.

A diagnosis of Juvenile Idiopathic Arthritis (JIA) is one of exclusion and blood tests and radiographs can be, and often are normal. Before planning invasive tests, a paediatric rheumatology assessment is recommended. Arthroscopy and synovial biopsy are rarely indicated except with concern about infection (mycobacterial), foreign body synovitis or malignancy.

If there is a delay in developmental milestones ensure that a CK test is done asap. This test is highly specific for muscular dystrophies. Also consider CK testing in any child with abnormal gait, speech delay, frequent falls and enlarged calves

Antinuclear antibody (ANA) is often found in normal healthy children and can be present in high titre with transient illness. ANA is not diagnostic of JIA or any other disease. In the context of JIA, the presence of ANA increases the risk of chronic anterior uveitis.

Rheumatoid factor (RF) is usually negative in children with JIA and is not diagnostic. In the context of JIA, RF associates with a more severe disease course.

A connective tissue disease diagnosis requires appropriate laboratory and imaging investigations after careful clinical assessment.

Imaging may be indicated but needs careful consideration. Young children may not co-operate with long procedures and may need sedation or anaesthesia. It is also important to minimise radiation exposure. Ultrasound or Magnetic Resonance Imaging (MRI) do not involve radiation but may not always be available. With suspected inflammatory disease, the MRI request with gadolinium is important as enhancement strongly suggests synovitis.

Radiographs for isolated severe or refractory joint pain – e.g. knee pain – should include the long bone above and below to help detect bone tumours. Radiographs to investigate hip disease should include frog leg lateral radiographs.

Please note: a pdf document of these Top Tips is also available here.