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.