magnesium (Mg+2) in 24 hour urine
Indications
- evaluation of hypomagnesemia
Reference interval
- 5.1-80 mg/24 hours (10.3-159.9 MEQ/24 hours)
Principle
About 40 per cent of the average adult daily dietary intake of magnesium (300 mg) is absorbed in the small intestine & excreted in the urine.
The absorption process appears to be poorly controlled, & homeostasis is maintained largely by renal excretion, which is regulated by tubular reabsorption.
The ACA magnesium method is a modification of the methylthymol blue (MTB) complexometric procedure.
MTB forms a blue complex with magnesium.
Calcium ilnterference is minimized by forming a complex between calcium & Ba-EGTA (chelating agent).
The amount of MG-MTB complex formed is proportional to the magnesium concentration & is measured using a two-filter (600-510 nm) end-point technique.
Clinical significance
Magnesium depletion is clinically more significant & frequent than an excess, with a prevalence of 11 per cent in hospitalized patients.
Signs & symptoms of magnesium depletion do not usually appear until extracellular levels have fallen to 1 MEQ/L or less.
Manifestations of significant magnesium depletion include weakness, muscle fasciculations, depression, agitation, seizures, hypocalcemia, hypokalemia, & cardiac arrhythmias.
Cause for symptomatic hypomagnesemia include malabsorption, severe diarrhea, nasogastric suction with administration of magnesium-free parenteral fluids, alcoholism, acute pancreatitis, early chronic renal disease, malnutrition, excessive lactation, chronic dialysis, digitalis intoxication, hyperparathyroidism, hypoparathyroidism, hyperaldosteronism, diabetes mellitus, diuretic therapy & porphyria with inappropriate secretion of antidiuretic hormone.
Increases
- alcohol intoxication
- Bartter's syndrome
- pharmaceuticals
Decreases
Specimen
2 mL aliquot of a 24-hour urine collection.
Proper 24 hour urine collection procedureshould be followed, & collection container should be refrigerated at 2-6 C during collection.
Upon receipt in the work area, it should be well-mixed & measured in a graduated cylinder.
The total volume should be recorded.
Acidify patient samples with 1 part concentrated HCL to 100 parts of urine prior to analysis.
Centrifuge if a precipitate forms.
More general terms
Additional terms
References
- ↑ Kaplan, Lawrence A. & Pesce, Amadeo J., Clinical Chemistry: Theory, Analysis, & Correlation, 2nd Edition, The C.V. Mosby Company, St. Louis, MO, 1989, pp. 875-879.
- ↑ Henry, John Bernard, M.D., Clinical Diagnosis & Management by Laboratory Methods, 18th Edition, W.B. Saunders Company, Philadelphia, PA, 1991, pp. 165-166.
- ↑ ACA IV Discrete Clinical Chemistry Analyzer Instrument Manual, Volume 3A, Chapter 6: Test Methodology, MG 8.
- ↑ Clinical Guide to Laboratory Tests, 4th edition, HB Wu ed, WB Saunders, Philadelphia, 2006
- ↑ Panel of 8 tests Laboratory Test Directory ARUP: http://www.aruplab.com/guides/ug/tests/0020477.jsp
- ↑ Panel of 29 tests Laboratory Test Directory ARUP: http://www.aruplab.com/guides/ug/tests/0020805.jsp