Understanding Common Blood Tests and What They Mean

If you're having surgery—even a minor procedure—the doctor may order blood tests. While interpreting blood tests are 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 provider 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 also often done after a procedure to look for bleeding, and to make sure that the organs are functioning well after surgery.

Many times these tests are performed routinely, often the night after surgery. This does not mean that there is an expectation that something is wrong, most often these tests confirm that everything is going well after surgery.

Patients in the ICU can expect to have more frequent blood tests. If you are on a ventilator you can expect an arterial blood gas to be drawn daily or even more often.

Chem 7

Also known as a blood chemistry, chemistry panel, or basic metabolic 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 further testing for diabetes.

The seven tests included are:

• Blood urea nitrogen (BUN)
• Serum glucose
• Creatinine
• Carbon dioxide (CO2)
• Serum chloride
• Serum sodium
• Serum potassium

CBC

A complete blood count (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 clotting issues.

After surgery, the doctor may order this test to see if a blood transfusion is warranted, or to evaluate for infection.

A CBC includes:

• White blood cell count (WBC)
• Red blood cell count (RBC)
• Platelet count (Plt)
• Hemoglobin
• Hematocrit

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

PT, PTT, and INR

These tests, known collectively as a coagulation panel, looks at the ability for your blood to clot. Disordered clotting ability can cause problems in surgery, during which bleeding is often expected.

If the result show impaired clotting ability, it may be necessary to delay surgery to prevent significant bleeding during the procedure. This test may also be used to monitor blood-thinning medications, such as Coumadin (warfarin).

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 bloodstream and normal blood clotting, it's essential to know if it's functioning normally prior to the procedure. Elevated numbers can indicate liver damage or poor liver function.

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), also known as SGOT
• Alanine aminotransferase (ALT), also known as SGPT
• Alkaline phosphatase (ALP)
• Total bilirubin
• Direct bilirubin
• Indirect bilirubin
• Albumin

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 or providers.

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.

You may be asked to sign a consent form for the administration of blood prior to your surgery, even if a transfusion is not a routine part of the procedure, in case the need arises.

Blood Culture and Sensitivity

A blood culture is a process where a small sample of your blood is drawn into a bottle of sterile culture medium that "feeds" bacteria. The sample is kept warm and after a few days, it is checked to see if bacteria is growing. If bacteria are growing, it is likely that the same bacteria is growing in your blood.

If bacteria grow, it is then exposed to different antibiotics to see which antibiotic is the most effective for treating your infection. This is a scientific way to choose the best antibiotic for your infection without giving you multiple antibiotics and hoping one works well.

A Word From Verywell

While it is helpful to have a general understanding of lab results and what they mean, the healthcare provider is ultimately responsible for interpreting the results and determining how to respond to them.

Interpreting lab results is a skill that is honed over the years, so don't feel a need to understand every nuance of your lab results. It is far more important that you listen closely when the provider is explaining their plan and how they would like to proceed with your care.