THE IMPORTANCE OF URINARY MAGNESIUM VALUES IN PATIENTS WITH GUT FAILURE

Objective: To determine whether urinary magnesium (Mg) values in patie nts with gut failure would be more helpful than serum Mg measurements in assessment of Mg deficiency. Design: We compared serum and urinary Mg values in 16 patients with gut failure and 16 age- and sex-matched control subjects. Material and Methods: Sixteen patients with gut fail ure (nine women and seven men; mean age, 59 years) had serum and 24-ho ur urinary Mg measured before Mg replacement therapy, Short bowel synd rome was present in 75%, and diffuse small bowel disease was present i n 25%. Results: The median value for serum Mg was 1.7 mg/dL for patien ts and 2.0 mg/dL for healthy control subjects (P<0.001). The median va lues for urinary Mg were 19 mg and 127 mg per 24-hour specimen in pati ent and control groups, respectively (P<0.001). A strong correlation w as noted between serum Mg and urinary Mg levels. All patients had low urinary Mg values even though 9 of 16 (56%) had normal serum Mg values , Two patients with normal serum Mg concentrations had urinary Mg valu es of 20 mg/24 h (25% of normal), Serum, but not urinary, Mg correlate d significantly with the length of remaining small bowel (P=0.03). Con clusion: Urinary Mg declines before serum Mg and is an earlier and mor e reliable indicator of evolving Mg deficiency, On the basis of these observations and those showing beneficial effects of parenterally admi nistered Mg supplements on urinary citrate excretion (and, presumably, formation of calcium oxalate stones), replacement of Mg in patients w ith gut failure should be targeted at normalizing urinary Mg.