Blood Gas Analysis and anion gap (which is calculated from serum electrolytes) are two different tests, done on different specimens by different professionals working in different laboratories (at least in the US). BGA measures bicarb, pO2, O2 saturation, etc in arterial blood. The anion gap is calculated from the electrolytes Na+, Cl- and HCO3- in venous serum. Blood gas analysis does not measure electrolytes. The anion gap is typically reported with a complete or basic metabolic panel, in which these electrolytes are measured. I don't know about the laboratory practices in other countries, but in the US, you must order blood gases and metabolic panels separately, from separate departments.