HCO lost is replaced by a chloride anion, and thus there is a normal anion gap. Gastrointestinal loss of HCO (i.e., diarrhea) (note: vomiting causes hypochloraemic alkalosis) Kidney loss of HCO (i.e., proximal renal tubular acidosis (RTA) also known as type 2 RTA) Kidney dysfunction (i.e., distal renal tubular acidosis also known as type 1 RTA) Renal hypoaldosterone (i.e., renal tubular acidosis also known as type IV RTA) characterized by elevated serum potassium. There are three types. 1. Low Renin may be due to diabetic nephropathy or NSAIDS (and others causes). 2. Low aldosterone may be due to adrenal disorders or ACE inhibitors. 3. Low response to aldosterone maybe due to potassium sparing diuretics, trimethoprim/sulfamethoxazole, or diabetes (and other causes). Ingestions Ammonium chloride and acetazolamide, ifosfamide. Hyperalimentation fluids (i.e., total parenteral nutrition) Some cases of ketoacidosis, particularly during rehydration with Na+ containing IV solutions. Alcohol (such as ethanol) can cause a high anion gap acidosis in some patients, but a mixed picture in others due to concurrent metabolic alkalosis. Mineralocorticoid deficiency (Addison's disease) Note: a useful mnemonic to remember this is FUSEDCARS – fistula (pancreatic), uretero-enterostomy, saline administration, endocrine (hyperparathyroidism), diarrhea, carbonic anhydrase inhibitors (acetazolamide), ammonium chloride, renal tubular acidosis, spironolactone. Low anion gap A low anion gap is often due to hypoalbuminemia. Albumin is an anionic protein and its loss results in the retention of other negatively charged ions such as chloride and bicarbonate. As bicarbonate and chloride anions are used to calculate the anion gap, there is a subsequent decrease. The anion gap is sometimes reduced in multiple myeloma, where there is an increase in plasma IgG (paraproteinaemia). Correcting the anion gap for the albumin concentration The calculated value of the anion gap should always be adjusted for variations in the serum albumin concentration. For example, in cases of hypoalbuminemia the calculated value of the anion gap should be increased by 2.3 to 2.5 mEq/L per each 1 g/dL decrease in serum albumin concentration (refer to Sample calculations, below). Common conditions that reduce serum albumin in the clinical setting are hemorrhage, nephrotic syndrome, intestinal obstruction and liver cirrhosis. Hypoalbuminemia is common in critically ill patients. The anion gap is often employed as a simple scanning tool by clinicians at the bedside to detect the presence of anions such as lactate, which can accumulate in critically ill patients. Hypoalbuminemia can mask a mild elevation of the anion gap, resulting