Contrast agents also can affect renal function and therefore should be avoided in patients with chronic kidney disease. CMR might be contraindicated in patients with claustrophobia or implanted devices, and use of gadolinium contrast agents is associated rarely with nephrogenic systemic fibrosis. For this reason, gadolinium is contraindicated in patients with severe renal dysfunction (estimated glomerular ), and the dose should be adjusted for patients with mild to moderate dysfunction (estimated glomerular filtration rates 30 to 60 mL/min per ). As with all safety considerations, the potential risks need to be considered carefully in concert with the potential benefits from the added information obtained to guide care. In addition to pretest likelihood, a variety of clinical factors influence noninvasive test selection.103 105 Chief among these are the patient s ability to exercise, body habitus, cardiac medication use, and ECG interpretability. The decision to add imaging in patients who have an interpretable ECG and are capable of vigorous exercise is important because imaging and nonimaging testing have different diagnostic accuracies, predictive values, and costs. Most, but not all, studies evaluating cohorts of patients undergoing both exercise ECG and stress imaging have shown that the addition of imaging information provides incremental benefit in terms of both diagnostic and prognostic information with an acceptable increase in cost (Section 2.2.1.5).106 117 Other factors affecting test choice include local availability of specific tests, local expertise in test performance and interpretation, the presence of multiple diagnostic or prog- nostic questions better addressed by one form of testing over another, and the existence of prior test results (especially when prior images are available for comparison). 