Abbott Laboratories said it would buy Alere Inc for $5.8 billion to become a leader in point-of-care testing, a fast-growing market as physicians increasingly adopt rapid tests that speed up treatment. Point-of-care tests provide results to doctors in a matter of minutes as they can be conducted in the physician's office, an ambulance or even at home. Waltham, Massachusetts-based Alere, which has annual sales of $2.5 billion, makes tests for infections such as HIV, tuberculosis, malaria and dengue.