For a blood count, blood is drawn from a vein in the arm or
fingertip, mixed with a diluting fluid, placed in a glass chamber so the number
of red and white blood cells can be counted. Red pigment (hemoglobin) in the
blood can be determined by comparison with color standards. The proportion of
red cells in relation to the rest of the blood can be established by whirling
the blood in a centrifuge so that heavier red cells settle in the bottom of a
small measured tube called a hematocrit.
Any departures from normal-such as too
little hemoglobin indicative of anemia, too few white cells indicative of
inability to combat infection, too many white cells indicative of body response
to an infection not otherwise apparent-can are noted quickly.
Blood, usually taken from a vein in small amounts, also may
be checked for sugar content as a test for diabetes and for the level of a
substance, uric acid, as a test for gout. And sophisticated new blood tests
often are valuable for heart problems, supplementing the information provided
by the electrocardiogram. The electrocardiogram, a record of the electrical
activity of the heart, is useful for analyzing any disturbances of heartrhythm, detecting inflammation, showing damage to the heart muscle, and making
other determinations. An electrocardiogram, taken in good health, is of value
because it provides a baseline for the future; it establishes what is normal
for the individual and allows better interpretation of any changes that occur
later. When a heart attack occurs-and many heart attacks are silent-an
electrocardiogram will show that it has occurred. But it may not show
accurately how much of the heart has been damaged.
