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Blood and Urine tests

Laboratory tests help establish a diagnosis and are integral to monitoring disease activity, safety of immunosuppressive medications and are important as part of clinical trials.

A few important points to note with investigations:  

  • Blood tests or urine tests or their results are not always needed for a referral. If there is clinical concern, do not delay making the referral.
  • Children with Juvenile Idiopathic Arthritis (JIA) can have normal blood tests.
  • Inflammatory markers (acute phase proteins) include C-reactive protein (CRP), Erythrocyte Sedimentation Rate (ESR) and Ferritin.
  • A sudden drop in ESR, or dramatic rise in serum ferritin with low or falling haemoglobin or platelet count suggests onset of macrophage activation syndrome.
  • Immunosuppressed children, particularly children using interleukin-1 or interleukin-6 blockade, may not mount a normal immune response to infection - the CRP may be misleadingly normal even in a child with sepsis.
  • Creatine Kinase (CK) is an enzyme which leaks out of damaged muscles and is elevated in muscular dystrophy or inflammatory muscle diseases.  In muscular dystrophies there is usually a rise in CK, often about 10-100x normal range.
  • Liver enzymes (AST [aspartate aminotransferase] and ALT [alanine aminotransferase]) are raised with liver inflammation (e.g., infection or medicines) but can also be raised in muscular dystrophy.
  • HLA B27 (human leukocyte antigen B27) is a genetic marker found in many healthy people. In the presence of inflammatory arthritis, HLA B27 associates with axial spine involvement and acute uveitis.
  • Rheumatoid Factor (RF) is not diagnostic for JIA;  less than 5% children with JIA are RF positive.
  • Antinuclear Antibodies (ANA) are found in up to 15% of healthy children and can occur with viral infection and other non-rheumatic conditions. A persistently positive ANA can associate with a rheumatological conditions including JSLE. A positive ANA occurs in some children with JIA and carry higher risk for chronic anterior uveitis.
  • Abnormal urinalysis occurs for many reasons such as renal disease in JSLE or infection.

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