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Arterial Blood Gas (ABG) Reference Normal Predicted Values Calculator

ABG Predicted Normal Values

Arterial blood gas analysis is important in managing patients with cardiopulmonary diseases. Crapo et al1 defined reference equations in 1999 for healthy non-smokers for arterial blood gas and CO - oximeter analytes at two different altitudes (sea level and 1400m). Full details on the methods and equipment used is available in their article.

It was found that ABG and CO oximeter analytes results depended on a patient's age, sex, height, and weight, as well as the ambient atmospheric pressure - which is the proxy measurement for altitude.

Reference Normal values defined here

The following parameters were measured in samples of the patient's arterial blood to obtain predicted normal values for a population.

PaO2 = Partial pressure of oxygen in the blood

PaCO2 = Partial pressure of carbon dioxide in the blood

pH of the blood

AaPO2 = Alveolar-arterial  PO2 difference, which is a measure of the difference between the alveolar concentration (A) of oxygen and the arterial concentration of oxygen
PaO2. In this reference, AaPO2 was calculated with the following equation:

AaPO2 = 0.2093 x (PB - 47) - PaCO2 x [0.2093 + (1.0 - 0.2093/R)]  - PaO2

where PB was the measured atmospheric pressure in mmHg, PaO2 and PaCO2 were the mean values measured for the subject, and R was assumed to be 0.8

SaO2 = Saturated oxygen, which is measured as the percent of hemoglobin binding sites in the bloodstream occupied by Oxygen.

CO oximeter variables were:

Hb = Hemoglobin

COHb = Carboxyhemoglobin, expressed as the percent of hemoglobin bound to carbon monoxide

MetHb= Methemoglobin percent, or the percent of the form of hemoglobin in the blood that cannot bind oxygen due to presence Fe3+ instead of Fe2+ in the normal state.

Use of this calculator:

Equations were made to predict the reference normal values of the above parameters based on a patient's age, sex, height, weight, and atmospheric pressure. To use the calculator please enter the required inputs and press "submit query".

For further reading on predicted values and their use the following books are also highly recommended:

Recommended books on spirometry


Required inputs:

Date of birth



Atmospheric pressure
Pressure units


Crapo 1999 Arterial Blood Gas Reference Values for Sea Level and an Altitude of 1,400 Meters ROBERT O. CRAPO, ROBERT L. JENSEN, MATHEW HEGEWALD, and DONALD P. TASHKIN American Journal of Respiratory and Critical Care Medicine 1999 160:5, 1525-1531
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