A non-invasive blood gas test is carried out by a method that utilizes a venous blood sample together with a pulse oximeter and a plurality of mathematical equations. The method generates the following data points of the blood: (i) the pH level; (ii) the [H+] concentration; (iii) the [HCO.sub.3--] concentration; (iv) the partial pressure of carbon dioxide; and (v) the oxygen saturation level. Mathematical formulas, tables, and chemical equations provide a simple method by which a doctor or other medical professional can easily calculate the blood gas data without the need for an arterial blood sample or specialized machines. Blood gas measurements are obtained from a patient in a faster, safer and less painful manner than tests that require an arterial blood sample. In another embodiment of the present invention, a system for locating a dysfunctional organ in a patient is disclosed.