Intended use

The Magnesium assay is used for the quantitation of magnesium in human serum, plasma, or urine.

Summary

Magnesium is an essential nutrient, which is involved in many biochemical functions. It has a structural role in nucleic acids and ribosomal particles, required as an activator for many enzymes and has a role in energy producing oxidative phosphorylation.

The normal body contains between 21 to 28 g magnesium, more than 50% of which is complexed with calcium and phosphate in bone. Only approximately 1% of the total magnesium is found in the extracellular fluid; hence, it tends to enter and leave cells under the same conditions as potassium. Approximately 35% of plasma magnesium is protein-bound, mainly to albumin, and therefore changes in albumin concentration may affect magnesium.

Hypomagnesemia results in the impairment of neuromuscular function and may develop in severe prolonged diarrhea, malabsorption syndromes, hyperaldosteronism, and diuretic therapy. Hypermagnesemia is seen in renal glomerular failure and diabetic coma.

Method

Enzymatic

Principle

Magnesium present in the sample is a cofactor in an enzymatic reaction with isocitrate dehydrogenase. The rate of increase in absorbance at 340nm, due to the formation of NADPH, is directly proportional to the magnesium concentration.

Specimen collection and handling

Suitable Specimens

Serum, plasma, and urine are acceptable specimens.

• Serum: Use non-hemolyzed serum collected by standard venipuncture techniques into glass or plastic tubes with or without gel barriers. Ensure complete clot formation has taken place prior to centrifugation. Centrifuge according to tube manufacturer’s instructions to ensure proper separation of serum from blood cells. Some specimens, especially those from patients receiving anticoagulant or thrombolytic therapy, may take longer to complete their clotting processes. Fibrin clots may subsequently form in these sera and the clots could cause erroneous test results.

• Plasma: Use plasma collected by standard venipuncture techniques into glass or plastic tubes. Acceptable anticoagulants are lithium heparin (with or without gel barrier) and sodium heparin. Ensure centrifugation is adequate to remove platelets. Centrifuge according to tube manufacturer’s instructions to ensure proper separation of plasma from blood cells.

• Urine: Urine specimens should be collected in no more than 2.5mL of 6N HCl per 100 mL or urine and 10 g/L of boric acid for a 24 hour specimen, to prevent precipitation of magnesium complexes.1

For total sample volume requirements, refer to the ASSAY PARAMETERS section of this package insert and Section 5 of the ARCHITECT System Operations Manual.

Specimen Storage

Serum, Plasma, and Urine

Temperature	Maximum Storage Serum/Plasma Urine*	Bibliographic Reference
20 to 25°C 2 to 8°C -20°C	7 days 3 days 7 days 3 days 1 year 1 year	6 6,7 6

*Acidify to pH < 2.

NOTE: Stored specimens must be inspected for particulates. If present, mix and centrifuge the specimen to remove particulates prior to testing.

Materials and Equipment Required

Materials Provided

3P68 Magnesium Reagent Kit

Materials Required but not Provided

• 1E65-05 Multiconstituent Calibrator

• Control Material

• Saline (0.85% to 0.90% NaCl) for specimens that require dilution

Reagents – working solutions

Reagent Kit

Magnesium is supplied as a liquid, ready-to-use, single reagent kit which contains:

3P68-22

R1 5 x 39 mL

R2 5x 11 mL

Estimated tests per kit: 1,000* serum/plasma

Estimated tests per kit: 670* urine

3P68-32

R1 10 x 71 mL

R2 10 x 18 mL

Estimated tests per kit: 3,750* serum/plasma

Estimated tests per kit: 2540* urine

*Calculation is based on the minimum reagent fill volume per kit.

Reactive Ingredients	Concentration
R1 Isocitrate dehydrogenase D-isocitrate potassium salt R2 NADP	2.2 U/mL 1.47 mg/mL 8.37 mg/mL

Inactive Ingredients: R1 and R2 contains sodium azide (0.1%) as a preservative.

Reagent Handling Remove air bubbles, if present in the reagent cartridge, with a new applicator stick. Alternatively, allow the reagent to sit at the appropriate storage temperature to allow the bubbles to dissipate. To minimize volume depletion, do not use a transfer pipette to remove the bubbles. CAUTION: Reagent bubbles may interfere with proper detection of reagent level in the cartridge, causing insufficient reagent aspiration which could impact results.

Storage and stability

Reagent Storage

Unopened reagents are stable until the expiration date when stored at 2 to 8°C.

Reagent stability is 30 days if the reagent is uncapped and onboard.

Indications of Deterioration

Instability or deterioration should be suspected if there are precipitates, visible signs of leakage, extreme turbidity, microbial growth, if calibration does not meet the appropriate package insert and/or ARCHITECT System Operations Manual criteria, or if controls do not meet the appropriate criteria.

Calibration

Calibration is stable for approximately 30 days (720 hours) and is required with a lot number change. Verify calibration with at least two levels of controls according to the established quality control requirements for your laboratory. If control results fall outside acceptable ranges, recalibration may be necessary.

The urine application uses the serum calibration.

For a detailed description of how to calibrate an assay, refer to Section 6 of the ARCHITECT System Operations Manual.

For information on calibrator standardization, refer to the Iron/Magnesium Calibrator (1E69) package insert.

Quality control

Quality Control will be performed every 24 hours using Bio Rad Multiqual Controls Level 1,2,3.

• If quality control results do not meet the acceptance criteria defined by your laboratory, patient values may be suspect. Follow the established quality control procedures for your laboratory. Recalibration may be necessary.

• Review quality control results and acceptance criteria following a change of reagent or calibrator

lot.

Preparation of Working Solutions

Not Applicable

Assay Procedure

For a detailed description of how to run an assay, refer to Section 5 of the ARCHITECT System Operations Manual.

Interpretation: reporting results

Refer to Appendix C of the ARCHITECT System Operations Manual for information on results calculations.

Representative performance data are given in the EXPECTED VALUES and SPECIFIC PERFORMANCE CHARACTERISTICS sections of this package insert. Results obtained in individual laboratories may vary.

Measuring Range:

Linearity

Magnesium serum is linear up to 0.60 to 9.50 mg/dL (0.25 to 3.90 mmol/L) for the serum/plasma. Magnesium urine is linear up to 1.81 mg/dL to 26.35 mg/dL (0.74 to 10.83 mmol/L). Linearity was verified using Clinical and Laboratory Standards Institute (CLSI) protocol NCCLS EP6-P.9

Limit of Detection (LOD)

The LOD for Magnesium serum is 0.10 mg/dL or 0.04 mmol/L. The LOD for Magnesium urine is 0.24 mg/dL or 0.10 mmol/L. The LOD represents the lowest concentration at which the analyte can be detected with 95% probability based on n ≥60 replicates of low-analyte level samples.

Limit of Quantitation (LOQ)

The LOQ for Magnesium serum is 0.16 md/dL or 0.07 mmol/L. The LOQ for Magnesium urine is 0.79 mg/dL or 0.33 mmol/L. The LOQ was determined from n ≥60 replicates of the low-analyte level samples and is defined as the lowest concentration at which a total allowable error of 15% or 0.3 mg/dL was met.

Dilutions

The ARCHITECT c Systems have an automatic dilution feature; refer to Section 2 of the ARCHITECT System Operations Manual for additional information.

Serum and Plasma: Specimens with magnesium values exceeding 9.50 mg/dL (3.90mmol/L) are flagged and may be diluted by following either the Manual Dilution Procedure.

Urine: Urine samples are automatically diluted 1:2.97 by the system using the Standard dilution option, and then the system automatically corrects the concentration by multiplying the result by the appropriate dilution factor. All samples should be initially tested using the STANDARD (1:3) Dilution Protocol. This dilution extends urine Magnesium linearity to 26.35 mg/dL (10.83 mmol/L), sample should be tested at a 1:9 automated dilution. Samples exceeding this concentration are flagged and may be diluted by following either the Automated Dilution Protocol or the Manual Dilution Procedure.

Serum/Plasma Automated Dilution Protocol

No dilutions on this assay.

Results outside the AMR will be reported with a < or > result.

Urine Automated Dilution Protocol

If using the Automated Dilution Protocol, the system performs a 1:9 dilution of the specimen and automatically corrects the concentration by multiplying the result by the appropriate dilution factor.

Precautions and Warnings

Precautions for Users

• For In Vitro Diagnostic Use.

• Do not use components beyond the expiration date.

• Do not mix materials from different kit lot numbers.

• CAUTION: This product requires the handling of human specimens.

It is recommended that all human sourced materials be considered potentially infectious and be handled in accordance with the OSHA Standard on Bloodborne Pathogens.2 Biosafety Level 23 or other appropriate biosafety practices4,5 should be used for materials that contain or are suspected of containing infectious agents.

• The following warning and precaution apply to R1 and R2

Contains sodium azide. EUH032	Contact with acids liberates very toxic gas.

This material and its container must be disposed of in a safe way.

NOTE: Refer to Section 8 of the ARCHITECT System Operations Manual for proper handling and disposal of reagents containing sodium azide.

• Safety Data Sheets are available at www.abbottdiagnostics.com or contact your local representative.

Limitations — interference

LIMITATIONS OF THE PROCEDURE

The Magnesium assay is susceptible to interference from hemoglobin. Refer to the Interference section of this package insert for additional details.

Do not use acetic acid, nitric acid, and sodium fluoride as urine preservatives.

Do not use more than 2.5 mL 6N HCl per 100 mL of urine. Excess hydrochloric acid may cause elevated results with this methodology.

Do not exceed 10 g/L boric acid.

Elevated Magnesium patient results may occur due to contamination from other sources of magnesium. Refer to RESULTS section of this package insert for additional information.

Refer to the SPECIMEN COLLECTION AND PREPARATION FOR ANALYSIS and SPECIFIC PERFORMANCE CHARACTERISTICS sections of this package insert.

Interfering Substance	Interferent Concentration	N	Magnesium
Target (mg/dL)	% Difference
Ascorbic acid	3.0 mg/dL (0.170 mmol/L)	7	2.1	1.37
3.0 mg/dL (0.170 mmol/L)	6	4.0	0.36
3.0 mg/dL (0.170 mmol/L)	7	6.4	0.18
Bilirubin, Conjugated	55.3 mg/dL (945.6 µmol/L)	7	1.9	1.68
55.9 mg/dL (955.9 µmol/L)	7	3.6	-2.33
56.5 mg/dL (966.2 µmol/L)	7	5.7	1.40
Bilirubin, Unconjugated	60.3 mg/dL (1031.1 µmol/L)	7	2.0	1.52
60.5 mg/dL (1034.6 µmol/L)	6	3.7	0.65
60.9 mg/dL (1041.4 µmol/L)	7	6.0	1.65
Calcium	28.0 mg/dL (7 mmol/L)	6	2.0	2.70
28.0 mg/dL (7 mmol/L)	7	3.8	3.86
28.0 mg/dL (7 mmol/L)	7	6.1	3.94
Copper	6.5 µg/mL (102.29 µmol/L)	10	2.0	0.40
6.5 µg/mL (102.29 µmol/L)	10	4.0	-0.30
6.5 µg/mL (102.29 µmol/L)	10	6.3	0.63
Glucose	1240 mg/dL (68.82 mmol/L)	7	2.1	-0.46
1311 mg/dL (72.76 mmol/L)	7	4.0	-0.44
1199 mg/dL (66.54 mmol/L)	6	6.4	-0.54
Hemoglobin	250 mg/dL (2.5 g/L)	7	2.1	5.24
1000 mg/dL (10.0 g/L)	6	3.9	6.50
1200 mg/dL (12.0 g/L)	7	6.4	6.66
Intralipid	2476 mg/dL (24.76 g/L)	7	2.0	1.36
2471 mg/dL (24.71 g/L)	7	3.7	0.38
2482 mg/dL (24.82 g/L)	7	6.1	-2.69
Iron	641 µg/dL (114.78 µmol/L)	10	2.0	0.80
641 µg/dL (114.78 µmol/L)	10	4.0	-0.22
641 µg/dL (114.78 µmol/L)	10	6.4	-0.92
L-Dopamine	5.0 mg/dL (0.255 mmol/L)	7	2.1	1.83
5.0 mg/dL (0.255 mmol/L)	6	4.0	1.10
5.0 mg/dL (0.255 mmol/L)	7	6.4	1.85
Triglyceride	3647 mg/dL (41.21 mmol/L)	10	2.0	-2.04
3598 mg/dL (40.66 mmol/L)	10	4.0	-1.60
3580 mg/dL (40.45 mmol/L)	10	5.8	-0.47
Zinc	4.3 µg/mL (65.77 µmol/L)	10	2.0	-0.54
4.3 µg/mL (65.77 µmol/L)	10	4.1	0.52
4.3 µg/mL (65.77 µmol/L)	10	6.4	0.67

The above solutions were prepared by addition of the interfering substances to human serum pool.

Drug Interference

The following drugs were tested for interference at the concentrations indicated using an acceptance criteria of ± 7.5% from the target value.

Interfering Substance	Interferent Concentration	N	Magnesium
Target (mg/dL)	% Difference
Acetaminophen	241 µg/mL (1592 µmol/L)	10	1.9	0.75
241 µg/mL (1592 µmol/L)	10	3.6	0.05
241 µg/mL (1592 µmol/L)	10	5.8	0.54
Ibuprofen	601 µg/mL (2915 µmol/L)	10	1.8	1.03
601 µg/mL (2915 µmol/L)	10	3.6	1.05
601 µg/mL (2915 µmol/L)	10	5.8	0.74
Salicylic Acid	71.96 mg/dL (5.21 mmol/L)	10	1.8	1.63
71.96 mg/dL (5.21 mmol/L)	10	3.7	0.68
71.96 mg/dL (5.21 mmol/L)	9	5.8	0.67
Sulfapyridine	300 mg/L (1.20 mmol/L)	3	1.5	-0.40
Sulfasalazine	300 mg/L (0.754 mmol/L)	3	1.5	1.50
Temozolomide	20 mg/L (0.10 mmol/L)	3	3.5	0.26
20 mg/L (0.10 mmol/L)	3	7.5	-1.11

Sulfapyridine and sulfasalazine solutions were prepared by addition of the interfering substances to human serum pool. Temozolomide was evaluated in human plasma.

Urine

Studies were conducted on the ARCHITECT cSystem based on guidance from CLSI EP07-A2.10Representative results are summarized below. Interference effects were assessed by Dose Response and Paired Difference methods. The following interfering substances were tested at the concentrations indicated using an acceptance criteria of ± 10% from the target value. Values in the table represent the highest levels of interferents that met the acceptance criteria at various magnesium concentrations.

Interfering Substance	Interferent Concentration	N	Magnesium
Target (mg/dL)	% Difference
Albumin	64.0 mg/dL (640 mg/L)	9	4.6	1.09
64.0 mg/dL (640 mg/L)	10	13.8	1.24
Ascorbic Acid	200 mg/dL (2000 mg/L)	9	4.9	0.76
200 mg/dL (2000 mg/L)	10	15.2	1.84
Bilirubin, Conjugated	59.9 mg/dL (1024.3 µmol/L)	10	4.3	-0.68
59.5 mg/dL (1017.5 µmol/L)	10	13.4	-2.41
Calcium	26.0 mg/dL (6.5 mmol/L)	9	4.9	2.39
27.0 mg/dL (6.8 mmol/L)	10	15.0	3.63
Copper	21.6 µg/dL (3.4 µmol/L)	12	5.1	-0.08
21.6 µg/dL (3.4 µmol/L)	12	14.5	0.20
Glucose	1220 mg/dL (67.71 mmol/L)	10	5.1	-0.92
1237 mg/dL (68.65 mmol/L)	10	15.6	3.04
Hemoglobin	1200 mg/dL (12.00 g/L)	10	5.2	4.36
1200 mg/dL (12.00 g/L)	9	15.9	2.10
Phosphorous	307 mg/dL (99 mmol/L)	10	4.5	-0.65
313 mg/dL (101 mmol/L)	9	14.1	-0.26
Zinc	3504 µg/L (54 µmol/L)	12	5.1	0.33
3504 µg/L (54 µmol/L)	12	14.6	0.03

Preservatives	Interferent Concentration	N	Magnesium
Target (mg/dL)	% Difference
Boric Acid	1000 mg/dL (10 g/L)	10	4.8	0.07
1000 mg/dL (10 g/L)	9	10.3	-0.63
6N HCl	3.0 mL/dL (180 mmol/L)	10	3.1	8.70
3.0 mL/dL (180 mmol/L)	10	9.4	8.76

Urine samples at the above concentrations were prepared by addition of the interfering substances to human urine pools.

NOTE: Acetic acid, nitric acid, and sodium fluoride interfere with magnesium results and should not be used as urine preservatives.

Interferences from medication or endogenous substances may affect results.11

Contacts:

Abbott Diagnostics Technical Support: 1-877-4ABBOTT (1-877-422-2688)

Alternative method

Send to sister facility if unable to perform at this site.

References

ABBOTT Magnesium package insert

Abbott Laboratories

Diagnostics Division

Abbott Park, Illinois 60064

PN 306624/R03

Revision 11/2018

Effective date

Effective date for this procedure: 06/11/2019

Author

Compiled by Abbott Diagnostics

Written by: Cheryl Strauch, MLS(ASCP)

Revised by: Jessica Mercer, MLS(ASCP)

Revised by: Rebecca Olog, MT(ASCP)

Revised by: Kimberlee J. Clark, MT(ASCP)