The above scenario is described as Raynaud's phenomenon, which is seen in Scleroderma. Raynaud's phenomenon Fibrosis of skin around digital blood vessels On Cold exposure due to abnormal vasoconstriction Tip of fingers turns white. Antinuclear antibody (ANA) is the most sensitive antibody in scleroderma and is the preferred screening test. Anti-centromere antibody is most specific for CREST syndrome. Anti-topoisomerase I (Scl-70)is most specific fordiffuse systemic sclerosis/diffused Scleroderma.