What Do Blood Test Results Mean?

Many blood test results come back either positive or negative. This means the result answers a yes or no question about something present in the blood. A positive test may mean a substance is present that shouldn't be, but it can also mean the opposite. A test that is positive for bacteria that shouldn't be present will help the doctor prescribe the best treatment. However, if the test is positive for a healthy level of immunity against a disease for which the patient was immunized, this tells the doctor nothing more needs to be done.

For some blood tests, there's a normal reference range. Any result that is higher or lower than the reference range is considered abnormal. For example, a healthy reference range for calcium levels in the blood is between eight and ten milligrams per deciliter (mg/dL). If the result is only a little outside the range, the doctor may or may not want to investigate further.

The complete blood cell count or CBC is one of the most common blood tests ordered by doctors and specialists. The test looks at levels of red and white blood cells as well as platelets. Red blood cells help carry oxygen and carbon dioxide in the body. White blood cells are part of the immune system, and platelets help with blood coagulation. Each of these cell types has a reference range that the doctor will use to assess a patient's health.

A lipid panel looks at levels of fats and cholesterol in the body, which are crucial to understanding the risk of cardiovascular disease. The panel measures levels of triglycerides, total cholesterol, and high- and low-density lipoproteins. Results that show high levels of cholesterol, low-density lipoproteins, and triglycerides may indicate a higher risk of heart disease. However, higher levels of high-density lipoproteins are desirable, as this cholesterol protects against heart disease.

Testing for blood glucose levels is commonly done during yearly physicals. Glucose refers to the sugars and starches we have in our blood as a result of metabolizing food. High levels indicate potential diabetes whereas low levels indicate hypoglycemia. Both of these conditions are abnormal and require further investigation. Doctors often require the patient to fast before the test, so he or she can determine the levels of glucose your body maintains without food.

The two tests that help doctors understand a blood-clotting ability are prothrombin time and partial thromboplastin time. Each of these tests measures the number of seconds it takes blood to clot when certain chemicals are added to a blood sample. If the results are outside the reference range, this could indicate a problem with prolonged clotting time. In other words, the person is at risk for excessive bleeding, and the doctor will investigate further to understand why.

The liver function tests look at bilirubin, alanine aminotransferase (ALT), alkaline phosphatase (ALP), aspartate aminotransferase (AST) and albumin. These common proteins show how well the liver is filtering toxins and producing required proteins for proper metabolism. In cases of acute liver problems or end-stage liver failure, these results will be outside the normal range.

The thyroid panel tests the functioning of your thyroid and pituitary gland. The thyroid is responsible for digestion, body heat, stress, and more. The panel looks at the thyroid-stimulating hormone produced by the pituitary. If this hormone is too low, the pituitary is not producing enough to stimulate the thyroid. If it's too high, it indicates the pituitary is working too hard. The panel also tests for levels of T3 and T4, which are produced by the thyroid. The T3 and T4 give the best indication if the thyroid is working correctly.

This test looks at levels of sodium, potassium, bicarbonate, and chloride. Maintaining a normal range for these electrolytes is crucial to the healthy functioning of body systems such as muscles, nerves, acid-base balance, and metabolism. Dehydration is often the cause of abnormal electrolyte results, but many health issues can contribute to results outside the normal range.

Blood results that are outside the normal reference range help the doctor identify what aspects require further investigation. Worrying about abnormal tests will only increase stress levels, which can exacerbate or cause symptoms. Instead, ask a doctor to clearly explain the expected or received results and the next steps. Most blood tests are done in combination with other blood or diagnostic tests. The results don't usually indicate something specific and require interpretation and further testing.