The most appropriate diagnostic test to perform next is aortic arteriography in this patient who most likely has Takayasu arteritis. She presents with arterial compromise in the setting of a systemic febrile illness. Asymmetric blood pressure in the arms suggests arm involvement, and a midabdominal bruit, leg symptoms, and hypertension suggest aortic and renal artery obstruction. The differential diagnosis includes other forms of vasculitis and/or thrombosis. Given her age, sex, and high erythrocyte sedimentation rate, a diagnosis of Takayasu arteritis is likely. Because there are no specific laboratory tests used to diagnose or define Takayasu arteritis, arteriography of the aorta and its branches is used to confirm the diagnosis and define the extent of the problem. Alternative imaging modalities such as CT angiography or MR angiography might also be used for the same purpose.

An antimyeloperoxidase antibody assay would be useful if microscopic polyangiitis (MPA) were a diagnostic consideration; however, the kidney disease seen in this patient is due to renal artery obstruction and occurs in the absence of active urine sediment such as would be expected in MPA glomerulonephritis. Moreover, peripheral artery involvement would not be expected in MPA, a small-vessel disease.

The presence of antiphospholipid antibodies would be consistent with the antiphospholipid antibody syndrome and with the presence of thrombotic disease potentially occluding the arm, aorta, and renal arteries. However, her normal prothrombin and partial thromboplastin times indicate the absence of a lupus anticoagulant (one criterion for antiphospholipid antibody syndrome), and the lack of elevation in fibrin degradation products (D-dimer) argues against a thrombotic disease.

Although Takayasu arteritis and giant cell arteritis (GCA) share remarkably similar pathology, GCA occurs in older patients and is characterized by temporal arteritis, whereas Takayasu arteritis is a disease of the young that rarely, if ever, involves temporal arteries. Thus, a temporal artery biopsy is not indicated.