Blood tests are used to determine levels of sugars, minerals or hormones; number of cells; organ function; effectiveness of drugs; or the presence of bacteria or viruses. The results of these tests are compared against a reference range or the values seen in 95 percent of a population.
One of the most common blood tests performed is a complete blood count, or CBC. CBCs determine the number of white blood cells, the volume of red blood cells (hemocrit), the amount of oxygen carried by the red blood cells (hemoglobin levels), and a count of your platelets. The levels of these cells, when compared to appropriate reference ranges, gives your health care provider information about many of your body's functions.
Another common test is a glucose test, which measures the levels of sugar in your blood. This test, usually done while fasting, tests for diabetes. A sample reference range for a healthy, fasting adult is 60 to 99 milligrams per deciliter.
Cholesterol, a fatty substance essential to building up cell membranes, is associated with heart disease at certain levels. A reference range for a healthy adult is a total cholesterol level of less than 200, with an LDL (low density lipoprotein, the kind that commonly leaves plaque deposits in arteries) level of 100 or less.
To measure the healthy function of the thyroid, levels of the thyroid hormone, thyroxine (T4) is measured. There are many tests that can measure T4 levels, but tests measuring "free" T4--the amount of T4 circulating freely in the blood--are most common. Normal ranges are determined by your health care provider and the testing lab, and will vary. However, high levels of T4 suggest hyperthyroidism (overactive thyroid), while lower levels are characteristic of hypothyroidism (underactive thyroid).
If you experience unexplained bleeding or are taking blood thinner medications (such as Warfarin), another very common—if not weekly—blood test you may experience is prothrombin time (PT) or international normalized ratio (INR). PT/INR tests measure the amount of time it takes for blood to clot. Overly slow or quick blood clot times may indicate bleeding disorders (such as hemophilia) or that the patient’s blood thinner medication dose must be adjusted. Your health care provider and testing lab can provide you with your healthy PT/INR range, but a normal reference range for clotting (in healthy adults) falls between 10 and 13 seconds.
Liver Function Tests
Liver function tests (LFTs) are a suite of tests that can be performed to measure the health and function of the liver. LFTs include several tests—levels of liver enzymes, cholesterol, and PT/ING—but a common component is testing for the proteins, albumin and globulin, in the blood. Abnormally high or low total protein testing (TP) can indicate malfunctions in the liver. A normal reference range for TP in a healthy adult is between 6.5 to 8.2 grams per deciliter.