Updated October 01, 2014.

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

If you're having surgery—even a minor procedure—the doctor may order blood tests. While interpreting blood tests is best left to a physician, it may be helpful to understand what the test is looking for, and what's considered a "normal" result.

There are hundreds of different blood tests that can be performed in a lab, but the most common are performed routinely before and after surgery; these tests are very common and should not be cause for alarm.

The physician wants to make sure the patient is in the best possible health for the procedure, and to diagnose any conditions that could cause preventable complications.

Blood testing is often done after a procedure to look for bleeding, and to make sure that the organs are functioning well after surgery.

Common Blood Tests:

Chem 7: Also known as a blood chemistry, or a chemistry panel, this test looks at the levels of essential enzymes in the blood, and also checks kidney function. In addition, the glucose level in the blood is obtained through this test and can indicate if a person needs testing for diabetes.

The seven tests included in a Chem 7 include:

• Blood Urea Nitrogen (BUN)
• Serum Glucose
• Creatinine
• Carbon Dioxide (CO2)
• Serum Chloride
• Serum Sodium
• Serum Potassium

Interpreting Chem 7 Results

CBC:

A complete blood count, or CBC, looks at the different cells that make up whole blood. A CBC can inform the doctor if the body is making the appropriate number of each type of cell, and it can also reflect signs of a current or recent infection, bleeding, or a clotting issues.

After surgery, the doctor may order this test to see if a blood transfusion is warranted, or if the patient is dehydrated and requires additional fluids.

A CBC includes:

• White Blood Count (WBC)
• Red Blood Count (RBC)
• Platelet Count (Plt)
• Hemoglobin
• Hematocrit

An "H&H" is similar to a CBC, but only looks at the hemoglobin and hematocrit levels.

The Complete Blood Count In Detail

PT, PTT & INR:

These tests, known collectively as a coagulation panel, look at how quickly blood clots. Elevated clotting times can cause problems in surgery, during which bleeding is often expected. If the result shows significantly longer clotting times than are typical, it may be necessary to delay surgery to prevent significant bleeding during the procedure.

About PT, PTT & INR Tests

Liver Enzymes:

Liver function studies, also known as LFTs, are done to determine if the liver is functioning normally. Because the liver plays a role in removing anesthesia from the blood stream and normal blood clotting, it's essential to know if it's functioning normally prior to the procedure. Elevated numbers can indicate poor liver function or liver damage.

An additional test, called a GGT, may be added to the liver panel. This test can indicate that there is damage to the liver or surrounding ducts, but does not specify what type of damage is present.

A typical liver function study includes:

• Aspartate Phosphatase (AST)
• Alanine Aminotransferase (ALT)
• Alkaline Phosphatase (ALP)
• Total Bilirubin
• Direct Bilirubin
• Indirect Bilirubin
• Albumin

More Information on Liver Function Tests

Arterial Blood Gas:

An arterial blood gas, commonly called an ABG, looks at how the respiratory system is functioning and how much oxygen is in the blood. This test requires blood from an artery, which is fully oxygenated by the lungs, and is typically drawn from the radial artery in the wrist. Abnormal results may indicate that the blood is low in oxygen, that the patient is breathing too much or too little (on a ventilator during the surgical procedure), or that they need additional oxygen.

The ABG is typically performed at least once a day when the patient is on a ventilator for an extended period of time. The results are used to determine if any changes in ventilator settings are necessary. If the patient is in ICU, a special IV called an arterial line may be placed to make drawing arterial blood easier, particularly when it's being done frequently.

A Typical ABG includes:

• pH: The acid/base balance of arterial blood
• PC02: How much carbon dioxide is in the blood
• PO2: How much oxygen is being concentrated in the blood
• HCO3: Bicarbonate levels may indicate kidney function issues
• O2: How much oxygen is available for the tissues of the body to use

ABG Interpretation is very challenging and is typically done by physicians.

ABO Typing: ABO Typing is the medical term for determining the patient's blood type. This is done prior to surgery, so blood can be given in the operating room if necessary. Most surgeries do not require a blood transfusion, but some procedures, such as on-pump heart bypass surgery, routinely require the administration of blood.