Blood Test Guide

The Blood Test Summary
What: Blood tests are done to check for possible diseases and disorders and to evaluate organ and muscle function.
Who: A physician will determine if a patient needs to have a blood test after an examination.
Where: tests are typically done in a doctor’s office or medical laboratory facility.
When: A blood test can be done at any time.
How: Whole blood or plasma have individual elements that can be counted and analyzed.
Type: Blood is drawn using a need inserted into a vein in the arm.
Why: Blood tests can help detect diseases and disorders and evaluate the effectiveness of medication.
Time: Results are delivered to a physician who will then evaluate them in conjunction with a physical examination. A patient may hear from their doctor within a few days.
Language: Not applicable.
Preparation: No preparation is needed for a blood test, though some blood tests require eight to twelve hours of fasting.
Cost: The cost of a blood test is generally covered under health insurance.

By Erin Hasinger, Tests.com


Blood tests help doctors check patients for diseases, conditions, organ functions and abnormalities. Blood tests are one of the factors used in the diagnosis of cancer, heart disease, HIV and AIDS and diabetes, among other diseases and conditions. Blood tests can also help evaluate the effectiveness of treatments and medications and identify risk factors for future disease.


Blood tests are typically ordered by a physician, and blood will be drawn either in a doctor’s office or laboratory facility. During a blood test, a nurse or a physician will use a needle to withdraw blood from a vein in one’s arm. A band is tied around the upper arm to stop blood flow and increase the size of the veins. This may feel tight. A needle is inserted into a vein, possibly causing a slight pinching feeling, and a tube is attached to the needle to collect the blood. Following blood collection, a piece of gauze or cotton should be placed on the insertion site to stop the bleeding, and then it should be covered with a bandage.


During the blood analysis, a lab technician may count blood cells or separate blood cells from plasma, which then is analyzed to measure substances in the blood.


One of the most common blood tests is the complete blood count, or CBC. This is used in the detection of diseases and conditions such as cancer, immune system disorders, anemia and infection. The CBC measures the amounts of:


·         Red blood cells

·         White blood cells

·         Platelets (fragments of blood cells used in clotting)

·         Hemoglobin (a red blood cell protein that carries oxygen)

·         Hematocrit (the space red blood cells occupies in blood)


The quantities of each can help doctors make a particular diagnosis. For example, abnormal red blood cell and hemoglobin numbers might indicate anemia, while abnormal white blood cell numbers might indicate an immune system disorder. Hematocrit is used to check for dehydration, anemia or bone marrow disorders.


Another common blood test is the basic metabolic panel, which is a group of tests used to measure chemicals in the plasma. A basic metabolic panel can help provide insight into the function of muscles, bones and organs. Tests evaluate:


·    Blood glucose, which is a type of sugar in the blood and can help indicate diabetes

·    Kidney function, tests for which measure the waste products the kidneys filter

·    Electrolytes, which are minerals such as sodium, chloride, bicarbonate and potassium, the measurements of which can be signs of heart failure, high blood pressure, or kidney or liver disease

·    Calcium, which can help indicate cancer, thyroid disease, bone disease, malnutrition or kidney problems


Blood tests generally do not require any preparation, though some tests, such as those evaluating glucose, may require one to fast for eight to twelve hours prior to the blood test. A physician will give the patient any instructions about fasting in advance of the blood test.


Risks from a blood test are low. A bruise may form at the needle site, though applying pressure using cotton or gauze immediately after the needle withdrawal can help prevent bruising. A rare complication is phlebitis, which is swelling of the vein. This is treated using a warm compress. Finally, ongoing bleeding can be a risk for those with bleeding disorders. A bleeding disorder should be discussed with a physician prior to having a blood test done.


To learn more about blood tests or to find a medical laboratory, visit the Blood Test Directory.