Blood Testing

What Is It?

Blood tests enable doctors to assess your health by analyzing cells, chemicals, proteins and other substances in your blood. Some tests are recommended regularly to see if blood levels of certain cells or chemicals fall within a normal range. Others are done to help diagnose health conditions, such as allergies, anemia, and diabetes.

There are two typical methods for taking a blood sample. One, called venipuncture, involves drawing a vial of blood from a vein, usually on the inner surface of your arm near your elbow. The other, called a finger stick, is done by pricking your finger with a sharp blade to obtain a small amount of blood from a capillary. The method used depends on how much blood is needed for the test you are having.

What It’s Used For

Blood tests can be used to screen for a wide variety of diseases and disorders. They are also used to determine how well treatment is working for many different conditions. The kinds of problems for which doctors order blood tests include:

  • Allergies
  • Anemia
  • Chemical balances in the body
  • Blood clotting problems
  • Heart disease
  • Hormone levels
  • Infection
  • Inflammation
  • Kidney disease
  • Lead poisoning
  • Liver function problems
  • Disorders of the pancreas 
  • Thyroid disorders


No preparation is needed for a blood test. Tell your doctor about any medications you are taking, both prescription and over-the-counter. Some medications can elevate or lower levels of certain substances in the bloodstream, interfering with the accuracy of the blood test.

Many factors can affect test results, including your:

  • age
  • sex
  • race
  • current medications
  • medical history
  • overall health
  • diet
  • adherence to test-prep instructions
  • variations in lab techniques.

If you have become lightheaded or fainted when you have had a blood test in the past, tell the professional before they start drawing your blood. You should lay flat when your blood is drawn. Sit up for a few minutes after the blood test is finished. Be careful when you stand up.

How It’s Done

An individual trained to draw blood will perform the procedure. If you have your blood drawn in a laboratory, the person drawing your blood will almost always be a blood-draw specialist called a phlebotomist. In the doctor’s office, the nurse, physician assistant or doctor will draw your blood.

The first step is to clean the area from which blood will be drawn, using an antiseptic solution. Blood is usually taken from a vein in the crook of the elbow or sometimes on the back of the hand. An elastic band is wrapped around the upper arm, cutting off blood flow to the arm and causing the veins to swell with blood. A sterile disposable needle is inserted into the vein and blood is drawn up through the needle into an airtight, attached plastic tube. The elastic arm band is then removed, followed by the needle. A bandage is placed over the puncture site and pressure is applied to stop the bleeding.

Your blood sample will be sent to a laboratory for analysis based on the type of tests being done. Sometimes, your doctor or a technician will perform the analysis in the office.


Results from the lab will be available in approximately 2–4 days for most types of blood tests. Some special tests may not be available for 7 – 10 days. Your doctor will receive a lab report and send the results to you within two weeks. Your doctor will contact you sooner if he or she wants you to take some action urgently.


There are almost no risks associated with having blood drawn. Depending on the accessibility of your veins, the professional drawing your blood may not be successful on the first try. Some people have small veins or veins that are not visible on the surface of the skin.

You may experience slight pain or a pinching or stinging sensation when the needle pierces the skin and enters the vein. Some people get a throbbing in the arm caused by the tight elastic band used to engorge the veins.

A little blood often seeps out of the vein where the needle was inserted, causing bruising under the skin. Bruising in the area may appear on the day following your blood test. There is no need to be concerned unless it is painful or the bruise continues to enlarge. Your body will reabsorb the blood that seeped out.

As with any procedure that breaks the skin, there is an extremely low risk of infection. Tell your doctor if the area becomes red, hot to the touch, painful, or if you develop a fever with these symptoms.

Some people feel faint or lightheaded, especially when a larger amount of blood is taken.

When to Call a Professional

Because harmful side effects are not expected, people typically need to call their doctors only to discuss laboratory results.

Bible verses for today’s meditation and inspiration: Matthew E. McLaren

But you, man of God, flee from all this, and pursue righteousness, godliness, faith, love, endurance and gentleness. 1 Timothy 6:11 NIV

For everyone born of God overcomes the world. This is the victory that has overcome the world, even our faith. 1 John 5:4 NIV

If I have the gift of prophecy and can fathom all mysteries and all knowledge, and if I have a faith that can move mountains, but do not have love, I am nothing. 1 Corinthians 13:2 NIV

I have chosen the way of faithfulness; I have set my heart on your laws. Psalm 119:30 NIV

“Go,” said Jesus, “your faith has healed you.” Immediately he received his sight and followed Jesus along the road. Mark 10:52 NIV

Then Jesus declared, “I am the bread of life. Whoever comes to me will never go hungry, and whoever believes in me will never be thirsty.” John 6:35 NIV

“‘If you can’?” said Jesus. “Everything is possible for one who believes.” Mark 9:23 NIV

For it is with your heart that you believe and are justified, and it is with your mouth that you profess your faith and are saved. Romans 10:10 NIV

And by faith even Sarah, who was past childbearing age, was enabled to bear children because she considered him faithful who had made the promise. Hebrews 11:11 NIV

For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life. John 3:16 NIV

So in Christ Jesus you are all children of God through faith, for all of you who were baptized into Christ have clothed yourselves with Christ. Galatians 3:26-27 NIV

For in the gospel the righteousness of God is revealed—a righteousness that is by faith from first to last, just as it is written: “The righteous will live by faith.” Romans 1:17 NIV

Whoever believes and is baptized will be saved, but whoever does not believe will be condemned. Mark 16:16 NIV

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