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ABG Practice Questions

Prepare for the Arterial Blood Gas Interpretation section of the NCLEX with ABG practice questions.

The ABG questions below will help you gain confidence for the ABG section of the NCLEX and allow you to get a better feel for the types of questions you will be asked.

ABG Practice 1Kansas State University
ABG Practice 2Hull York Medical School
ABG Practice 3ED4Nurses

If you want to practice other sections of the NCLEX, visit our NCLEX practice test home.

Other ABG Resources

ABG practice tests are not the only way to prepare and study for the ABG section. There are online resources like flashcards that you can use to prepare for the exam as well.

Quizlet 1Quizlet
Quizlet 2Quizlet
Quizlet 3Quizlet
Quizlet 4Quizlet

ABGS Examples

  1. Describe what a patient presenting with this ABG reading may be suffering from:
  • pH = 7.1
  • PCO2 = 40 mm
  • HgHCO3 = 18

(Answer: metabolic acidosis, patient likely has ketoacidosis, body will lower CO2 to be more basic)

  1. What is the normal range for PCO2?
  1. 15-25
  2. 35-45
  3. 55-65
  4. 15-35

(Answer: b. 35-45)

  1. Diagnose a patient that presents with this ABG reading:
  • pH = 7.48
  • PCO2 = 37 mm Hg
  • PO2 = 91 mm Hg
  • Sa O2 = 97%
  • HCO3 = 38 mEq/L

(Answer: uncompensated metabolic acidosis)

ABG Questions and the NCLEX

There are between 85 and 150 questions on the NCLEX. There are also four main sections, of which, ABG can be found in the Reduction of Risk Potential portion in the Physiological Integrity section of the NCLEX exam.

This makes up 9% to 15% of the exam.

Since this makes up a decent chunk of the NCLEX, it is important to study ABGs effectively. The first thing you need to know is that there are six steps to check a patient’s ABG.

  1. Check pH: You need to know if a patient’s blood is acidic, basic, or normal. While 7.4 is the most “normal” reading, nurses tolerate anywhere from 7.35 to 7.45. Less than 7.35 would be acidic meaning acidosis while more than 7.45 would be basic meaning alkalosis.
  2. Look at PCO2: CO2 is brought into the body and eliminated in the lungs. A change in PCO2 could reflect pulmonary issues. A normal PCO2 is between 35 and 45 mm Hg. Below 35 mm Hg could indicate hyperventilation (alkalotic) and above 45 mm Hg could indicate retention (acidotic).
  3. Examine HCO3: Produced by the kidneys, a patient’s bicarbonate levels should be between 22 and 26 mEq/L. This represents a normal metabolic component in your patient’s blood gas. Higher than 26 mEq/L is alkalotic and below 22 mEq/L is acidotic.
  4. Match either PCO2 or HCO3 to pH: If pH and PCO2 match and HCO3 is normal, then you either have respiratory alkalosis or acidosis. If the HCO3 and pH are the same with the PCO2 being normal, your patient has metabolic alkalosis or acidosis.
  5. See if PCO2 or HCO3 oppose the pH: If one of the systems becomes acidotic or alkalotic, the other will compensate for it to get the body back to normal. If the patient suffers from pulmonary acidosis, they may have metabolic alkalosis to compensate.
  6. Check O2 and SaO2: All patients should have an O2 of 80 mm Hg or more and a SaO2 of 95% or more. If one is low, the patient has hypoxemia. However, a patient being supplemented with O2 may have an O2 over 100 mm Hg and that is normal.

As you can see from the steps above, ABG tests can tell a nurse or doctor a lot about the patient and how their body is functioning. There are really four things that a nurse can check by looking at the ABG levels. They can see if the patient is:

  1. Acidotic
  2. Alkalotic
  3. Compensating
  4. Hypoxemic

ABG Tips

There is actually an easy way to check ABG using what is called the ABG Tic-Tac-Toe Method. The three main things checked in ABG interpretation are alkalosis or acidosis; respiratory or metabolic; and fully compensated, partially compensated, or uncompensated.

Here’s how to use this method:

  1. Set up your Tic-Tac-Toe board
  2. Put acidosis, normal, and alkalosis in the first row
  3. Determine the pH in the second row
  4. Place the PCO2 and HCO3 in the third row
  5. Check for respiratory or metabolic issues
  6. Look for compensation

Here is what an example would look like:

Patient results: pH = 7.1, PCO2 = 48 mm Hg, HCO3 = 30


Respiratory Acidosis, partially compensated

Because the pH and PCO2 of this patient are both acidotic, you are dealing with respiratory acidosis, and with the HCO3 being opposite of the pH, this is partially compensated. If the pH were in the middle and the PCO2 and HCO3 values were the same, it would be fully compensated.

Here is another example using this method:

Patient results: pH = 7.49, PCO2 = 39 mm Hg, HCO3 = 27


Metabolic Alkalosis, uncompensated

Since the pH and HCO3 values are both alkalotic, you know that this patient suffers from metabolic alkalosis. The PCO2 being unaffected by the patient’s metabolic alkalosis means that the patient’s body is not compensating for this issue.

Frequently Asked Questions

Yes, there are ABG questions on the NCLEX. You will find them in the reduction of risk potential section, which makes up 9-15% of the exam.

The ABG questions are in the reduction of risk potential section which makes up 9% to 15% of the NCLEX exam.

Depending on the number of questions you get you can expect to see anywhere from 8 to 22 questions in this section.

Absolutely. ABG quizzes are one of the best ways to prepare for the ABG questions you will see on the NCLEX.

Jan Olson
Dr. Jan Olson has her Bachelor's degree in nursing, Master's degree in nursing, and Doctorate in nursing.