there is anion and cation
cation is positive charge ions (NA is the main part of cation which represent 90% of circulating cation)
anion chloride and bicarbonate (negative charge ions) which represent 85% of circulating anions
so what's anion gap ?
represent the anions that not routinely measured , include sulfate , phosphate , proteins and organic acids (lactic acid and ketones acids)
those anions not routinely measured so we calculate the anion gap to determine if those anions present in circulation and it amount in cases that rise suspection especially in acidotic conditions
how to calculate anion gap ?
NA-(cl +HCO3 )= 8-14 mEq/L (unmeasured anions in extracellular fluid)
>14 in acidotic conditions like lactic acidosis , ketoacidosis
< 8 like in hypermagnesiumia and paraprotein anemia