Normal & Abnormal Results

Normal Ranges

Full Blood Count

• The haematological indices reflect the severity of the systemic inflammatory process.
• Children with Oligoarticular JIA usually have normal blood counts whereas children with systemic onset arthritis can show marked thrombocytosis and leukocytosis (predominantly polymorphs).
• A normocytic normochromic anaemia of chronic illness can develop in chronic inflammatory disease and iron deficiency is common in children with long-standing or severe disease.
• Autoimmune haemolytic anaemia can complicate systemic inflammatory illness (e.g. Juvenile Systemic Lupus Erythematosus - JSLE).
• Unexpected cytopenia (such as low/normal platelet or white cell counts) in children with marked systemic inflammation can suggest the possibility of JSLE, occult malignancy (e.g. leukaemia or lymphoma) or development of a serious complication called macrophage activation syndrome which can lead to multisystem failure and high mortality.  

Inflammatory markers

• Inflammatory markers are useful measures of disease activity and central to the assessment of febrile children on immunosuppressive medications. They can also be used to monitor progress and response to treatment.
• The C-reactive protein (CRP) is an acute phase protein, rising very rapidly in response to acute inflammation or infection.
• The Erythrocyte Sedimentation Rate (ESR) will rise more slowly and remain elevated for a longer period of time following the onset of inflammation. Unlike CRP, ESR is influenced by many factors such as anaemia, pregnancy or hyperlipidaemias.
• In the absence of a definitive gold standard assay of disease activity, the ESR is frequently used to assess disease activity at presentation and during follow-up of children with rheumatic illnesses.
• The ESR is central to the majority of composite indices of disease activity developed for the paediatric rheumatic illnesses (for example, the Juvenile Arthritis Disease Activity Score or JADAS).
• A sudden drop in the ESR can herald the onset of macrophage activation syndrome in children with systemic onset JIA or JSLE.
• In the context of a child with potential JSLE, the CRP is typically normal and the ESR raised. The presence of a normal CRP in JSLE effectively excludes concurrent infection.
• Immunosuppressed children, particularly children using interleukin-1 or interleukin-6 blockade, may not mount a normal immune response to infection. Acute phase reactants such as the CRP must be interpreted with caution in this situation as they can be misleadingly normal even in a child with sepsis. 
• Serum immunoglobulins and the C4 complement factor reflect the acute phase reactants and can be markedly elevated in children with very active inflammatory disease. Low C3 or C4 complement factors can suggest active JSLE.

Ferritin

• The serum ferritin is an acute phase reactant and can be markedly elevated in systemic onset JIA.
• In the child with suspected systemic JIA, ferritin levels are typically raised.
• A sudden dramatic rise in the serum ferritin in association with low or falling haematological indices suggests the onset of macrophage activation syndrome.

Creatine Kinase (CK)

• In muscular dystrophies there is a rise in CK, often about 10-100x normal range.
• CK is an enzyme which leaks out of damaged muscles.
• It is elevated in muscular dystrophy or inflammatory muscle diseases.
• Liver enzymes (AST and ALT) can also be raised in muscular dystrophy. These enzymes are not only produced by the liver but also by muscle (in response to damage). Elevated liver enzymes in the presence of muscular dystrophy does therefore not reflect liver damage but muscle damage.
• Normal CK levels do not exclude an inherited muscle condition.
• High levels (> 500 IU/L) can occur after activity or a fall.

HLA B27

• The presence of HLA B27 is common in many healthy people.
• In the presence of inflammatory arthritis, HLA B27 can associate with axial spine involvement (which may present later on with pain / stiffness in the neck or lower back) and acute uveitis (which will cause a painful red eye and different to the chronic anterior uveitis observed in many cases of Juvenile Idiopathic Arthritis). This has implications for eye screening.