Is There A Blood Test For Connective Tissue Disease?
There are several blood tests done to diagnose connective tissue disease. There are mixed connective tissue diseases (MCTD) and undifferentiated connective tissue diseases (UCTD). The diagnosis of connective tissues disease is difficult as the symptoms tend to occur one after the other for a long period and the symptoms and signs can be present due to another disease. The medical history, physical examination and investigations should be taken into account before the diagnosis.
There are several blood tests done for mixed connective tissue diseases
- Complete blood cell count – reduced hemoglobin and red blood cells (anemia) and reduced white blood cells (leukopenia) can be seen.
- Erythrocyte sedimentation rate (ESR) – can be elevated
- C-reactive protein (CRP) – usually not elevated
- Blood for muscle enzymes creatinine kinase – if there is muscle damage then creatinine kinase levels can be increased.
- Immunological studies
- Antinuclear antibodies (ANA) – positive in patients with systemic lupus erythematosus patients (SLE), this test is very sensitive in detecting SLE but less specific.
- Anti- double-strand DNA antibodies (anti-ds DNA) – more specific in diagnosing SLE.
- Anti–U1-ribonucleoprotein (RNP) antibodies – anti-RNP bodies are needed for the diagnosis of MCTD and usually titers are typically high (95-100%). Anti–U1-RNP is characteristic of MCTD. Anti-RNP antibodies are helpful in the disease monitoring as well because, these become undetectable when the disease goes into a remission stage.
High-titer speckled pattern fluorescent antinuclear antibody (FANA) – seen typically in MCTD, however this is not specific for MCTD.
- Antiphospholipid antibodies (anticardiolipin antibodies and lupus anticoagulant) – if these are positive it can be pulmonary hypertension is present.
- Rheumatoid factor – this can be positive in many of the patients with MCTD.
- Scleroderma-specific antibodies – anti-centromere, anti–Scl-70 (topoisomerase), and anti–PM-1 (Pm-Scl).
- Liver profile – to check the liver functions.
- Serum amylase and lipase levels – to assess the pancreatic function.
Blood Tests For Undifferentiated Connective Tissue Diseases
UCTD is diagnosed when someone have symptoms and signs of connective tissue disease, but doesn’t fit into a specific type. Blood test will be helpful in identifying autoimmune inflammatory diseases.
- Complete blood count
- Serum creatinine
- Immunological studies
- Rheumatoid factor and anti-citrullinated cyclic peptide antibodies (anti-CCP) – rheumatoid factor can be present in UCTD, but both tests positive suggest rheumatoid arthritis.
- ANA – In UCTD the most common pattern will be speckled or less commonly homogenous.
- Anti-dsDNA – if this is positive it suggests SLE.
- C3 and C4 – usually normal in UCTD. If the levels are reduced its more suggestive of SLE.
- Anti-histone antibody – this is positive in drug induced lupus.
- Anti-Ro/SSA and La/SSB antibodies – commonly positive in SLE, sub-acute LE and Sjogren’s syndrome but SSA may be present in UCTD. Anti-Ro/SSA immunoglobulin G (IgG) antibodies are very common in UCTD.
- Anti-centromere and Scl-70 antibodies – these are highly specific for limited and generalized scleroderma in symptomatic patients.
- Anti-cardiolipin antibody and anti-beta 2 glycoprotein antibody panels – these can be positive in antiphospholipid syndrome and in SLE.
- Antibodies to myositis antigens – positive if polymyositis and dermatomyositis is present.
- Angiotensin converting enzyme – this can be positive in 50% of patients with sarcoidosis.
There are two types of connective tissue disease: mixed connective tissue diseases (MCTD) and undifferentiated connective tissue diseases (UCTD). The diagnosis of connective tissues disease is difficult as the symptoms tend to occur one after the other for a long period and the symptoms and signs can be present due to another disease. The medical history, physical examination and investigations should be taken into account before the diagnosis. Blood tests done for MCTD and UCTD are CBS, ESR, CRP, creatinine kinase, ANA, anti-ds DNA, antiphospholipid antibodies, rheumatoid factor and CCP. Anti–U1-ribonucleoprotein (RNP) antibodies are specific for MCTD and Anti-Ro/SSA immunoglobulin G (IgG) is commonly seen in UCTD.
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