Hi, Anion gap provides an estimate of the unmeasured anions in plasma. Anion gap = [Measured Cations(+ions)] - [Measured Anions(-ions)] Normal anion gap acidosis is where in the blood pH is acidic (less than 7.35) and the anion gap (unmeasured anions) in normal (12 +/- 4 or 7 +/- 4 as per some labs). This is seen in Diarrhea (gastrointestinal bicarbonate loss), Renal tubular acidosis, and in intake of drugs like ammonium chloride, hydrochloric acid. Reduced/negative anion gap acidosis is where in the blood pH is acidic and the anion gap is less than normal, seen in Hypoalbuminemia, Hypercalcemia, Hyperkalemia, Hypermagnesemia, Lithium toxicity, Multiple Myeloma. High anion gap is seen when the unmeasured anions are more as in conditions like Methanol Toxicity, Uremia, Diabetic Ketoacidosis, Lactic Acidosis, Dehydration. High anion gap is also seen when the unmeasured cations are decreased as in Hypocalcemia, Hypokalemia, Hypomagnesemia. Hypoproteinemia is the condition where in the plasma proteins are less than normal(6 to 8.3 gm/dl). One common cause is Protien loss in urine seen several Nephropathies.