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

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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).