Investigations
1st investigations to order
clinical diagnosis
Test
In most cases, a good history and physical examination are sufficient for diagnosis. However, as secondary RP may pre-date a connective tissue disease or may coincide with the onset of underlying conditions (e.g., diffuse cutaneous systemic sclerosis or polymyositis), all patients presenting with RP should undergo further testing where available.[4]
Result
clinical features of RP
antinuclear antibody
Test
Ordered if connective tissue disease, especially systemic lupus erythematosus, is suspected.
Normal in primary RP.
In secondary RP is often positive with a centromere pattern.
Approximately 30% of RP patients with a positive, centromere pattern antinuclear antibody (ANA) will develop a connective tissue disease in the following 5 years.[28]
Result
strongly positive ANA or uncommon pattern such as centromere or nucleolar are suggestive of secondary RP; however, a positive ANA is common in the general population
FBC
Test
Normal in primary RP, may be abnormal in secondary RP. Any connective tissue disease may cause anaemia. In systemic lupus erythematosus, cytopenias are often present.
Result
normal in primary RP; may show low WBC, anaemia, and low platelet count in secondary RP
erythrocyte sedimentation rate
Test
Normal in primary RP, may be elevated in secondary RP.
Result
normal in primary RP; may be elevated in secondary RP
C-reactive protein
Test
Normal in primary RP, may be elevated in secondary RP.
Result
normal in primary RP; may be elevated in secondary RP
urinalysis
Test
Normal in primary RP; may show RBCs and/or protein in secondary RP such as in systemic lupus erythematosus or vasculitis with active glomerulonephritis.
Result
normal in primary RP; may show RBCs and/or protein in secondary RP
Investigations to consider
capillaroscopy
Test
Not usually performed in primary care. Used to identify abnormalities suggestive of underlying connective tissue disease, such as dilated capillaries at the nailbeds.
Result
normal in primary RP; dilated capillaries suggestive of secondary RP
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