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A-a Gradient

Aka: A-a Gradient, Alveolar-Arterial Oxygen Tension Difference, (A-a) PO2 difference, (A-a) DO2

See Also
1. Arterial Blood Gas
Physiology
1. Efficiency of gas exchange between alveolus and artery
Calculation at sea level
1. A-a Gradient = PaO2 - FIO2 x (760 - 47) - (PaCO2/0.8)
2. FIO2 on room air = 0.21
Normal A-a Gradient
1. A-a Gradient = (Age/4) + 4
2. Young person at sea level
  1. A-a increases 5 to 7 mmHg for every 10% increase FIO2
  2. Room Air: 10 to 20 mmHg
  3. 100% oxygen: 60 to 70 mmHg
3. Increased age affects A-a Gradient (at sea level)
  1. Age 20 years: 4 to 17 mmHg
  2. Age 40 years: 10 to 24 mmHg
  3. Age 60 years: 17 to 31 mmHg
  4. Age 80 years: 25 to 38 mmHg
Increased A-a Gradient
1. Pulmonary Embolism

Family Practice Notebook

Patients should address specific medical concerns with their physicians.

Although access to this page is not restricted, the information found here is intended for use by medical providers.

This page was written by Scott Moses, MD, last revised on 10/21/2007 and last published on 5/17/2012.

This is one of 5740 pages in the Family Practice Notebook