Test ID: MGU
Magnesium, 24 Hour, Urine
Secondary ID 
A test code used for billing and in test definitions created prior to November 2011
NY State Approved Indicates the status of NY State approval and if the test is orderable for NY State clients.
Useful For Suggests clinical disorders or settings where the test may be helpful
Assessing the cause of abnormal serum magnesium concentrations
Determining whether the body is receiving adequate nutrition
Special Instructions and Forms Describes specimen collection and preparation information, test algorithms, and other information pertinent to test. Also includes pertinent information and consent forms to be used when requesting a particular test
Method Name A short description of the method used to perform the test
Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES)
Reporting Name A shorter/abbreviated version of the Published Name for a test; an abbreviated test name
Aliases Lists additional common names for a test, as an aid in searching
Mg (Magnesium)
Specimen Type Describes the specimen type needed for testing
Specimen Required Defines the optimal specimen. This field describes the type of specimen required to perform the test and the preferred volume to complete testing. The volume allows automated processing, fastest throughput and, when indicated, repeat or reflex testing.
Collection Container/Tube: Clean, plastic urine container with no metal cap or glued insert
Submission Container/Tube: Plastic, 10-mL urine tube (Supply T068) or a clean, plastic urine container with no metal cap or glued insert
Specimen Volume: 10 mL
Collection Instructions:
1. Collect urine for 24 hours.
2. No preservative.
3. See Metals Analysis-Collection and Transport in Special Instructions for complete instructions.
4. Refrigerate specimen within 4 hours of completion of 24-hour collection.
Additional Information:
1. 24-Hour volume is required.
2. See Urine Preservatives in Special Instructions for multiple collections.
Urine Preservative Collection Options
| Ambient | Yes |
| Refrigerated | Preferred |
| Frozen | Yes |
| 6N HCl | Yes |
| 50% Acetic Acid | Yes |
| Na2CO3 | No |
| Toluene | Yes |
| 6N HNO3 | Yes |
| Boric Acid | Yes |
| Thymol | No |
Specimen Minimum Volume Defines the amount of specimen required to perform an assay once, including instrument and container dead space. Submitting the minimum specimen volume makes it impossible to repeat the test or perform confirmatory or perform reflex testing. In some situations, a minimum specimen volume may result in a QNS (quantity not sufficient) result, requiring a second specimen to be collected.
Reject Due To Identifies specimen types and conditions that may cause the specimen to be rejected
| Hemolysis | NA |
| Lipemia | NA |
| Icterus | NA |
| Other | NA |
Specimen Stability Information Provides a description of the temperatures required to transport a specimen to the laboratory. Alternate acceptable temperature(s) are also included.
| Specimen Type | Temperature | Time |
|---|---|---|
| Urine | Refrigerated (preferred) | 28 days |
| Ambient | 7 days | |
| Frozen | 7 days |
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Magnesium, along with potassium, is a major intracellular cation. Magnesium is a cofactor of many enzyme systems. All adenosine triphosphate-dependent enzymatic reactions require magnesium as a cofactor. Approximately 70% of magnesium ions are stored in bone. The remainder is involved in intermediary metabolic processes; about 70% is present in free form, while the other 30% is bound to proteins (especially albumin), citrates, phosphate, and other complex formers. The serum magnesium level is kept constant within very narrow limits. Regulation takes place mainly via the kidneys, primarily in the ascending loop of Henle.
Conditions that interfere with glomerular filtration result in retention of magnesium and, hence, elevation of serum concentrations. Hypermagnesemia is found in acute and chronic renal failure, magnesium overload, and magnesium release from the intracellular space. Mild-to-moderate hypermagnesemia may prolong atrioventricular conduction time. Magnesium toxicity may result in central nervous system depression, cardiac arrest, and respiratory arrest.
Numerous studies have shown a correlation between magnesium deficiency and changes in calcium-, potassium-, and phosphate-homeostasis, which are associated with cardiac disorders such as ventricular arrhythmias that cannot be treated by conventional therapy, increased sensitivity to digoxin, coronary artery spasms, and sudden death. Additional concurrent symptoms include neuromuscular and neuropsychiatric disorders. Conditions associated with hypomagnesemia include chronic alcoholism, childhood malnutrition, lactation, malabsorption, acute pancreatitis, hypothyroidism, chronic glomerulonephritis, aldosteronism, and prolonged intravenous feeding.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
0-15 years: not established
> or =16 years: 75-150 mg/specimen
Interpretation Provides information to assist in interpretation of the test results
With normal dietary intake of 200 to 500 mg of magnesium per day, urine excretion is typically 75 to 150 mg/24 hours. The remainder of the dietary intake passes through the gastrointestinal tract and is excreted in the feces.
Decreased renal function, such as in dehydration, diabetic acidosis, or Addison's disease, results in reduced output of magnesium.
Poor diet (alcoholism), malabsorption, and hypoparathyroidism result in low urine magnesium due to low uptake from the diet.
Chronic glomerulonephritis, aldosteronism, and drug therapy (cyclosporine, thiazide diuretics) enhance excretion, resulting in high output of magnesium.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Magnesium forms insoluble complexes with normal urine constituents that precipitate as soon as urine is passed. Sodium bicarbonate must not be used as a preservative. Acidification not required.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Fentona TR, Eliasziw M, Lyon SC, et al: Low 5-year stability of within-patient ion excretion and urine pH in fasting-morning-urine specimens. Nutr Res 2009;29:320-326
2. Mircetic RN, Dodig S, Raos M, et al: Magnesium concentration in plasma, leukocytes and urine of children with intermittent asthma. Clin Chim Acta 2001;312:197-203
Method Description Describes how the test is performed and provides a method-specific reference
Magnesium concentrations in urine can be determined by inductively coupled plasma optical emission spectrometry. Aqueous acidic calibrating standards, quality control samples, patient specimens, and blanks are diluted with diluent containing an internal standard. In turn, all diluted blanks, calibrating standards, quality control samples, and patient specimens are aspirated into a pneumatic nebulizer and the resulting aerosol directed to the hot plasma discharge by a flow of argon. In the annular plasma the aerosol is vaporized, atomized, and then ionized. Emission signals from magnesium and the internal standard are observed radially by the emission spectrometer. Instrumentation response is defined by the linear relationship of analyte concentrations versus the ratio of the magnesium emission signals ratioed with the internal standard. After reagent blank subtraction, unknown sample magnesium concentrations are calculated by entering the net unknown intensity ratios into the linear calibration equation.(Nixon DE, Moyer TP, Johnson P, et al: Routine measurement of calcium, magnesium, copper, zinc, and iron in urine and serum by inductively coupled plasma emission spectroscopy. Clin Chem 1986;32:1660-1665)
Day(s) and Time(s) Test Performed Outlines the days and times the test is performed. This field reflects the day and time the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time required before the test is performed. Some tests are listed as continuously performed, which means assays are performed several times during the day.
Monday through Friday; 11 a.m. to 6 p.m.
Analytic Time Defines the amount of time it takes the laboratory to setup and perform the test. This is defined in number of days. The shortest interval of time expressed is "same day/1 day," which means the results may be available the same day that the sample is received in the testing laboratory. One day means results are available 1 day after the sample is received in the laboratory.
Maximum Laboratory Time Defines the maximum time from specimen receipt at Mayo Medical Laboratories until the release of the test result
Specimen Retention Time Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded
Performing Laboratory Location The location of the laboratory that performs the test
Test Classification Provides information regarding the medical device classification for laboratory test kits and reagents. Tests may be classified as cleared or approved by the US Food and Drug Administration (FDA) and used per manufacturer's instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR), Investigation Use Only (IUO) product, or a Research Use Only (RUO) product.
CPT Code Information Provides guidance in determining the appropriate Current Procedural Terminology (CPT) code(s) information for each test or profile. The listed CPT codes reflect Mayo Medical Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.
83735
LOINC® Code Information Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the result codes returned for this test or profile.
| Result ID | Reporting Name | LOINC Code |
|---|---|---|
| 8595 | Magnesium, 24 Hr, U | 24447-5 |
| TM52 | Collection Duration | 13362-9 |
| VL50 | Urine Volume | 3167-4 |
| 857 | Mg Concentration | 32024-2 |
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