Test ID: MGF
Magnesium, Random, Feces
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
Diagnosis of osmotic diarrhea due to excessive ingestion of magnesium
Ruling out excessive ingestion of magnesium in the work-up of chronic diarrhea
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
Lytes, Feces
Magnesium (Mg)
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.
Container/Tube: Stool container (Supply T291)
Specimen Volume: 20 g
Collection Instructions:
1. Collect a very liquid stool specimen.
2. See Stool Collection Information Sheet in Special Instructions.
Additional Information:
1. Do not send formed stool. In the event a formed stool is submitted, the test will not be performed. The report will indicate "A formed stool specimen was submitted for analysis. This test was not performed because it only has clinical value if performed on a watery stool specimen."
2. High concentrations of gadolinium and iodine are known to interfere with most metals tests. If either gadolinium- or iodine-containing contrast media has been administered, a specimen must not be collected for 96 hours.
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 | Formed stool |
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 |
|---|---|---|
| Fecal | Frozen (preferred) | 14 days |
| Refrigerated | 14 days | |
| Ambient | 7 days |
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Magnesium is a normal constituent in the diet and is normally present in fecal material. Magnesium is also a commonly used laxative that can be the cause of chronic diarrhea.
Sodium, potassium, chloride, and sulfate are usually the major contributors to fecal osmolality. Fecal osmolality is normally 2 x (sodium + potassium) unless there are exogenous factors inducing a change in this ratio, such as the presence of other osmotic agents (magnesium sulfate, saccharides), or drugs inducing secretions, such as phenolphthalein or bisacodyl.
If magnesium is excreted at a high rate (>200 mEq/kg), with an osmotic gap >100 mOsm/kg, magnesium is likely to be the principle contributor to osmotic diarrhea. Use of magnesium salts in the form of over-the-counter stool softeners is the most likely source of such excess excretion.
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: 0-199 mEq/kg
Interpretation Provides information to assist in interpretation of the test results
The osmotic theory of diarrhea is explained by the equation: 2x (stool sodium + stool potassium) = stool Osmolality + or - 30 mOsm.
Normal fecal sodium and potassium in the presence of an osmotic gap (>30 mOsm/kg) suggests osmotic diarrhea.
Increased concentration of fecal magnesium contributes to osmotic diarrhea.
Magnesium concentration of >200 mEq/kg is frequently associated with decreased fecal sodium and potassium, and is an indicator of excessive consumption of magnesium that is likely the cause of diarrhea.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
This test will only be performed on watery stool (diarrhea).
Formed stools are highly unlikely to contain excessive concentrations of magnesium. Formed stools indicate normal osmolality, ruling out excessive magnesium concentration. In the event a formed stool is submitted, the test will not be performed, and the report will indicate: "A formed stool specimen was submitted for analysis. This test was not performed because it only has clinical value if performed on a naturally occurring watery stool specimen."
High concentrations of gadolinium and iodine are known to interfere with most metals tests. If either gadolinium- or iodine-containing contrast media has been administered, a specimen must not be collected for 96 hours.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Phillips S, Donaldson L, Geisler K, et al: Stool composition in factitial diarrhea: a 6-year experience with stool analysis. Ann Intern Med 1995;123:97-100
2. Ho J, Moyer T, Phillips S: Chronic diarrhea: the role of magnesium. Mayo Clin Proc 1995;70:1091-1092
3. Fine KD, Santa Ana CA, Fordtran JS: Diagnosis of magnesium-induced diarrhea. N Engl J Med 1991;324:1012-1017
Method Description Describes how the test is performed and provides a method-specific reference
A small fraction of weighed feces is digested in hydrochloric acid and then analyzed for magnesium concentration (along with sodium and potassium) by inductively coupled plasma-atomic emission spectroscopy (ICP-AES). (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; evening
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 |
|---|---|---|
| 32290 | Magnesium, Random, F | 26708-8 |
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