Ordering of Magnesium and Phosphorous Labs in the Inpatient Setting Connie Tien June 6, 2016

Methods Inclusion criteria: All inpatients on Teams A-G who were still hospitalized on June 5, 2016. Chart review: Number resulted was used as a surrogate marker of number ordered 8 day period from May 29, 2016 to June 5, 2016 Number of serum magnesium and phosphorous resulted Number of magnesium and/or phosphorous resulted on June 5th Normal or abnormal result Review of the progress note or H&P from June 4th to determine if there was an indication for the test(s) to be ordered for the following morning (June 5th) Healthcare Bluebook: Magnesium $18 Phosphorous $13

Some Causes of Mg and Phos Abnormalities Hypomagnesemia Hypophosphatemia Hyperphosphatemia Gastrointestinal Losses Diarrhea Malabsorption and steatorrhea Acute pancreatitis Renal Losses Medications Diuretics (loop and thiazide) Volume expansion Uncontrolled diabetes mellitus Alcoholism Hypercalcemia Acquired tubular dysfunction (recovery from ATN, postobstructive diuresis, post-renal transplantation) Internal Redistribution Increased insulin secretion, particularly during refeeding Acute respiratory alkalosis Hungry bone syndrome Decreased Intestinal Absorption Inadequate intake Inhibition of phosphate absorption (e.g. antacids, phosphate binders, niacin) Steatorrhea and chronic diarrhea Vitamin D deficiency or resistance Decreased Urinary Excretion Primary and secondary hyperparathyroidism Fanconi syndrome Other – acetazolamide, tenofovir, IV iron, chemotherapeutic agents Removal by Renal Replacement Therapies Acute Phosphate Load Endogenous Cell lysis (tumor lysis syndrome, rhabdomyolysis) Exogenous Phosphate-containing medications (laxatives, fosphenytoin) Intestinal uptake Cellular Shift Lactic or ketoacidosis Decreased Renal Clearance Reduced GFR Acute kidney injury Chronic kidney injury Increased Tubular Reabsorption Hypoparathyroidism or pseudohypoparathyroidism Acromegaly Bisphosphonates Vitamin D toxicity (also increases intestinal absorption) Pseudohyperphosphatemia Hyperglobulinemia Hyperlipidemia Hemolysis Hyperbilirubinemia Medications (amphotericin B, heparin, tissue plasminogen activator) From UpToDate

Over an 8 day period from May 29th to June 5th, among 62 patients: Results Over an 8 day period from May 29th to June 5th, among 62 patients: Magnesium Phosphorous 252 tests were ordered Mean and median of 4 tests were ordered per patient Range 1 to 12 tests 52% (n=32) patients had no magnesium abnormalities and among these patients: Range 1 to 8 tests 34% (n=11) of those patients had some documented indication 217 tests were ordered Mean of 3 and median of 2 tests were ordered per patient Range 1 to 11 tests 47% (n=29) patients had no phosphorous abnormalities and among these patients: Mean and median of 2 tests were ordered per patient 17% (n=5) of those patients had some documented indication

Results On June 5th Magnesium Phosphorous 82% (n=51) patients had magnesium levels ordered and among these patients: 35% (n=18) had some documented indication 31% (n=16) had an abnormal result 73% (n=45) patients had phosphorous levels ordered and among these patients: 36% (n=16) had some documented indication 24% (n=11) had an abnormal result 70% (n=44) patients had both a magnesium and phosphorous level ordered and among these patients: 14% (n=6) of those patients had abnormalities in both magnesium and phosphorous

Results Among the patients with magnesium and/or phosphorous levels on June 5th, 18 patients had some documented indication. Among those patients, 100% (n=18) had a magnesium level ordered and 89% (n=16) had a phosphorous level ordered Documented indications included: ESRD Diuresis for acute decompensated heart failure or ascites Acute pancreatitis Refeeding syndrome Malnutrition from anorexia nervosa, alcoholism, cancer Paroxysmal atrial fibrillation to check for electrolyte abnormalities as an etiology

Conclusions There is over ordering of magnesium and phosphorous levels in the inpatient setting. This may be due to a combination of workplace expectations and/or lack of understanding of testing indications. Even among the approximately 50% of individuals in this analysis with no magnesium abnormalities during their hospitalization, a mean of 4 magnesium tests were ordered per patient at an estimated total cost of at least $72 per patient (4 x $18). Even among the approximately 50% of individuals in this analysis with no phosphorous abnormalities during their hospitalization, a mean of 2 tests were ordered per patient at an estimated total cost of at least $26 per patient (2 x $13).