ABG interpretation practice 2026

Thirty arterial blood gas practice cases. Each gives a pH, a PaCO2 and an HCO3−; you pick the interpretation, and the answer comes with the steps that lead to it.

The cases use the normal ranges pH 7.35 to 7.45, PaCO2 35 to 45 mmHg and HCO3− 22 to 26 mEq/L. [MedlinePlus] The answers use the ROME method that nursing programs teach. [RegisteredNurseRN: ROME] If you want the method first, start with how to interpret an ABG.

30 cases. Read the three values, then pick the interpretation.

  1. Case 1 of 30Adult arterial gas

    pH 7.21, PaCO₂ 64 mmHg, HCO₃⁻ 25 mEq/L. Which interpretation fits these values?

  2. Case 2 of 30Adult arterial gas

    pH 7.47, PaCO₂ 31 mmHg, HCO₃⁻ 22 mEq/L. Which interpretation fits these values?

  3. Case 3 of 30Adult arterial gas

    pH 7.20, PaCO₂ 42 mmHg, HCO₃⁻ 16 mEq/L. Which interpretation fits these values?

  4. Case 4 of 30Adult arterial gas

    pH 7.49, PaCO₂ 42 mmHg, HCO₃⁻ 31 mEq/L. Which interpretation fits these values?

  5. Case 5 of 30Adult arterial gas

    pH 7.25, PaCO₂ 68 mmHg, HCO₃⁻ 29 mEq/L. Which interpretation fits these values?

  6. Case 6 of 30Adult arterial gas

    pH 7.46, PaCO₂ 25 mmHg, HCO₃⁻ 17 mEq/L. Which interpretation fits these values?

  7. Case 7 of 30Adult arterial gas

    pH 7.20, PaCO₂ 32 mmHg, HCO₃⁻ 12 mEq/L. Which interpretation fits these values?

  8. Case 8 of 30Adult arterial gas

    pH 7.46, PaCO₂ 48 mmHg, HCO₃⁻ 33 mEq/L. Which interpretation fits these values?

  9. Case 9 of 30Adult arterial gas

    pH 7.36, PaCO₂ 55 mmHg, HCO₃⁻ 30 mEq/L. Which interpretation fits these values?

  10. Case 10 of 30Adult arterial gas

    pH 7.41, PaCO₂ 31 mmHg, HCO₃⁻ 19 mEq/L. Which interpretation fits these values?

  11. Case 11 of 30Adult arterial gas

    pH 7.37, PaCO₂ 34 mmHg, HCO₃⁻ 19 mEq/L. Which interpretation fits these values?

  12. Case 12 of 30Adult arterial gas

    pH 7.41, PaCO₂ 51 mmHg, HCO₃⁻ 31 mEq/L. Which interpretation fits these values?

  13. Case 13 of 30Adult arterial gas

    pH 7.05, PaCO₂ 60 mmHg, HCO₃⁻ 16 mEq/L. Which interpretation fits these values?

  14. Case 14 of 30Adult arterial gas

    pH 7.58, PaCO₂ 33 mmHg, HCO₃⁻ 30 mEq/L. Which interpretation fits these values?

  15. Case 15 of 30Adult arterial gas

    pH 7.36, PaCO₂ 42 mmHg, HCO₃⁻ 23 mEq/L. Which interpretation fits these values?

  16. Case 16 of 30Adult arterial gas

    pH 7.25, PaCO₂ 62 mmHg, HCO₃⁻ 26 mEq/L. Which interpretation fits these values?

  17. Case 17 of 30Adult arterial gas

    pH 7.54, PaCO₂ 28 mmHg, HCO₃⁻ 23 mEq/L. Which interpretation fits these values?

  18. Case 18 of 30Adult arterial gas

    pH 7.28, PaCO₂ 40 mmHg, HCO₃⁻ 18 mEq/L. Which interpretation fits these values?

  19. Case 19 of 30Adult arterial gas

    pH 7.55, PaCO₂ 40 mmHg, HCO₃⁻ 34 mEq/L. Which interpretation fits these values?

  20. Case 20 of 30Adult arterial gas

    pH 7.30, PaCO₂ 67 mmHg, HCO₃⁻ 32 mEq/L. Which interpretation fits these values?

  21. Case 21 of 30Adult arterial gas

    pH 7.50, PaCO₂ 24 mmHg, HCO₃⁻ 18 mEq/L. Which interpretation fits these values?

  22. Case 22 of 30Adult arterial gas

    pH 7.28, PaCO₂ 31 mmHg, HCO₃⁻ 14 mEq/L. Which interpretation fits these values?

  23. Case 23 of 30Adult arterial gas

    pH 7.49, PaCO₂ 50 mmHg, HCO₃⁻ 37 mEq/L. Which interpretation fits these values?

  24. Case 24 of 30Adult arterial gas

    pH 7.37, PaCO₂ 56 mmHg, HCO₃⁻ 31 mEq/L. Which interpretation fits these values?

  25. Case 25 of 30Adult arterial gas

    pH 7.43, PaCO₂ 31 mmHg, HCO₃⁻ 20 mEq/L. Which interpretation fits these values?

  26. Case 26 of 30Adult arterial gas

    pH 7.38, PaCO₂ 33 mmHg, HCO₃⁻ 19 mEq/L. Which interpretation fits these values?

  27. Case 27 of 30Adult arterial gas

    pH 7.43, PaCO₂ 50 mmHg, HCO₃⁻ 32 mEq/L. Which interpretation fits these values?

  28. Case 28 of 30Adult arterial gas

    pH 7.12, PaCO₂ 57 mmHg, HCO₃⁻ 18 mEq/L. Which interpretation fits these values?

  29. Case 29 of 30Adult arterial gas

    pH 7.64, PaCO₂ 31 mmHg, HCO₃⁻ 32 mEq/L. Which interpretation fits these values?

  30. Case 30 of 30Adult arterial gas

    pH 7.40, PaCO₂ 40 mmHg, HCO₃⁻ 24 mEq/L. Which interpretation fits these values?

Where these come from: our app builds its practice cases from 15 textbook patterns, one for each combination of disorder and compensation, plus combined acidosis, combined alkalosis and normal. Its classifier was checked against 50 reference cases and a 27-cell table of every combination of high, normal and low in September 2026, and the cases it can serve were re-checked against an independent reading in October (319 cases; one that the 7.40 rule does not settle is left out here, and so is any case whose pH sits exactly on 7.35 or 7.45). Answers use the ROME method as nursing programs teach it. A case labelled fully compensated is the ROME reading of where the numbers sit; the Merck Manual says compensation cannot return the pH completely to normal, and the expected-compensation line under each answer, the same one our app shows, will read several of these as a second disorder. These are practice cases for study, not for care of a patient.

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Keep practicing in ABG Interpretation & Practice

For iPhone. Works offline.

These thirty cases come from our app’s drill. Type any pH, PaCO₂ and HCO₃⁻ into the app and it names the disorder with the ROME steps, then checks the compensation against the published formulas, including Winter’s. Then drill graded cases, with the missed ones coming back until you get them right. It works offline and needs no account.

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The rest of this guide

  • How to interpret an ABG, step by step: Read an arterial blood gas in five steps: pH, PaCO2, HCO3, the primary disorder (ROME), then compensation. Plain steps with the normal ranges and a check for a mixed disorder.
  • Normal ABG values: Normal arterial blood gas ranges: pH 7.35 to 7.45, PaCO2 35 to 45 mmHg, HCO3 22 to 26 mEq/L, PaO2 75 to 100 mmHg. What each value tells you, and what acidemia means.
  • ABG compensation rules: How much the lungs and kidneys should compensate in each acid-base disorder, with Merck Manual's expected-compensation formulas, and how to tell compensation from a mixed disorder.
  • Winter's formula: Winter's formula for metabolic acidosis: expected PaCO2 = 1.5 x HCO3 + 8, plus or minus 2. A worked example, and what it means when the measured PaCO2 is higher or lower.
  • ABG interpretation examples: Seven worked arterial blood gas examples, each read step by step: respiratory and metabolic acidosis and alkalosis, partial and full compensation, and a combined acidosis.
  • ABG interpretation FAQ: Short answers to common arterial blood gas questions: normal values, acidemia versus acidosis, what ROME means, full compensation, why HCO3 is calculated, and mixed disorders.

What these cases are, and are not

An ABG alone usually cannot give a diagnosis. [MedlinePlus] These cases teach the pattern: which value is driving the pH, and whether the other system has moved. They are study material, not a way to decide care for a patient.

The names “partially compensated” and “fully compensated” are the ROME teaching labels. In practice, a normal pH with abnormal PaCO2 and HCO3− can be one compensated disorder or a mixed one, and the Merck Manual says compensation cannot return the pH completely to normal. [Merck Manual: acid-base disorders] The compensation rules page covers how to check.

Sources

Every fact on this page was checked against these sources on . noshu is not affiliated with Merck, the National Library of Medicine or any source named here, and this is a study aid, not clinical guidance: your program, your institution’s protocols and a qualified clinician decide what is done for a patient. If something here is wrong, tell us at a@noshu.net.