Visiting Basics - age adjustment for A-a Gradient
As we are encountering more and more geriatric population with pulmonary symptoms, it is advisible to remind house staff to first adjust normal A-a Gradient value per age before jumping to calculate PAO2. Normal Gradient of 80 years old patient may not be consider acceptable for 20 years old.
Two quick formulae for age adjustment are:
1. Normal A-a Gradient = Age/4 + 4
(For 80 years old is 24 but for 20 years old is 9)
2. Normal A-a gradient = (Age+10) / 4
(For 80 years old is 22.5 but for 20 years old is 7.5)
(A-a Gradient = Alveolar-arterial Gradient)
See Nice Review on A-a Gradient - Dr. Lawrence Martin.