ABG interpretation FAQ
Short answers to the questions people ask most about reading an arterial blood gas. Each one links to the page it comes from.
What are normal ABG values?
pH 7.35 to 7.45, PaCO2 35 to 45 mmHg, HCO3 22 to 26 mEq/L, PaO2 75 to 100 mmHg and oxygen saturation 95 to 100%. Your report lists its own ranges, so use those on a real result. [MedlinePlus] Normal ABG values.
What is the difference between acidemia and acidosis?
Acidemia is a blood pH below 7.35. Acidosis is the process that causes acid to build up or base to be lost. Alkalemia (pH above 7.45) and alkalosis work the same way. [Merck Manual: acid-base disorders]
How do you interpret an ABG?
Check the pH, then PaCO2 and HCO3, then decide which one explains the pH, then see whether the other has moved to compensate, then check the compensation is the expected size. [Merck Manual: acid-base disorders] The five steps.
What does ROME mean in ABG interpretation?
Respiratory Opposite, Metabolic Equal. If PaCO2 and pH move in opposite directions the disorder is respiratory; if HCO3 and pH move the same way it is metabolic. [RegisteredNurseRN: ROME]
What does fully compensated mean on an ABG?
In the ROME labels, the pH is back in the normal range while the other value is abnormal in the opposite direction. The Merck Manual notes that compensation cannot return the pH completely to normal, so a gas read as fully compensated should still be checked against the expected compensation. [RegisteredNurseRN: ROME] [Merck Manual: acid-base disorders] Compensation rules.
Can a normal pH still mean a problem?
Yes. Compensation moves the pH toward the normal range, and in mixed disorders the Merck Manual says values may be deceptively normal. [Merck Manual: acid-base disorders]
What is Winter's formula?
Predicted PaCO2 = 1.5 x HCO3 + 8, plus or minus 2. It is applied in metabolic acidosis: a measured PaCO2 above the band means a respiratory acidosis is also present, and below it a respiratory alkalosis. [Merck Manual: acid-base disorders] Winter's formula.
What is a mixed acid-base disorder?
Two or more primary disturbances at once. If the compensation is not the expected size, the Merck Manual says to suspect a second primary process. [Merck Manual: acid-base disorders]
How long does compensation take?
The lungs respond over minutes to hours. The kidneys change how they handle bicarbonate hours to days after the change. [Merck Manual: acid-base regulation]
Is the HCO3 on an ABG measured?
Not directly. The ABG measures pH and PaCO2, and the HCO3 reported on the blood gas panel is calculated with the Henderson-Hasselbalch equation. The HCO3 on a serum chemistry panel is measured directly, and the Merck Manual considers it more accurate if the two differ. [Merck Manual: acid-base disorders]
Can an ABG alone give a diagnosis?
Usually not. MedlinePlus says an ABG alone usually cannot provide a diagnosis, and results are best explained by your provider. [MedlinePlus]
Are the practice cases here from a real exam?
No. They are practice cases from our app, which builds them from textbook patterns for each disorder and compensation state. They are for study, not for the care of a patient. The practice cases.
Sources
- MedlinePlus (National Library of Medicine), Arterial Blood Gas (ABG) Test, last updated June 26, 2025
- Merck Manual Professional Edition, Acid-Base Disorders (Lewis; peer reviewed by Braunstein), last updated April 2025
- Merck Manual Professional Edition, Acid-Base Regulation (Lewis; peer reviewed by Braunstein), last updated March 2025
- RegisteredNurseRN, ROME Method ABG Interpretation: Uncompensated vs. Compensated (nursing education)
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.