The purpose of screening in clinical practice is to identify the likelihood of a particular disease in asymptomatic persons. Screening differs from case findings in that screening is done in asymptomatic persons based primarily on age and gender. Case findings depend on information about a patient's symptoms and risk for disease. Before a screening test can be effective, certain criteria must be met, including the following: (1) the disease must have serious consequences, a long preclinical phase and effective treatment; (2) the screening test must have high sensitivity and specificity, be low in cost and acceptable to patients; and (3) the risks and costs of false-positive and false-negative results must be low, there must be consensus on management of patients with positive results and there must be a system in place for referral and treatment. Hensrud reviews current screening practices for cancer, hypertension and hyperlipidemia in primary care.

Many organizations have issued recommendations for cancer screening, including the American Cancer Society, the U.S. Preventive Services Task Force and the Institute for Clinical Systems Integration. For a review of their guidelines, see the accompanying table. These guidelines were designed for use in asymptomatic persons and should be modified on the basis of a patient's risk factors.

Current guidelines for hypertension screening recommend that all adults have a blood pressure check at least every two years. Readings should be repeated annually in patients with systolic readings between 130 and 139 mg Hg or diastolic readings between 85 and 89 mm Hg. Adults whose blood pressure is higher than 140/90 mm Hg should be reevaluated and should have blood pressure rechecked more often, depending on the level of elevation. Primary preventive strategies include weight loss, increased physical activity and, possibly, decreased consumption of sodium and alcohol. One randomized controlled trial also reported impressive results in treatment and prevention of hypertension in patients consuming a low-fat diet that was also high in fruits and vegetables.

Current recommendations for cholesterol screening advise that serum total cholesterol and high-density lipoprotein cholesterol levels be checked every five years. Primary prevention strategies consist of diet and exercise. Initial treatment for high cholesterol levels is the step diet regimen developed by the National Cholesterol Education Program and the American Heart Association.