A prominent hilar shadow on the chest x-ray of a 21 year old non-smoker suggests sarcoidosis, pulmonary hypertension or lymphoma. Other considerations include tuberculosis or a fungal infection, while lung cancer is an unlikely diagnosis. However, in some cases the isolated x-ray abnormality is not significant for any disease. To evaluate it further, a CT-scan and an electrocardiogram would be needed, and they may suggest the need for a bronchoscopy and a biopsy of any solid lesion. Sputum examination may not be reliable, and blood tests cannot provide a definitive diagnosis. Skin testing for tuberculosis would be significant if the test was positive, provided it was known to be negative previously.