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Test Code LAB3400 OB Magnesium, Blood Level

Test Name Alias

OB Magnesium Blood Level, OB Mg Blood Level, obstetric | 365

Ordering Instructions

This test is limited to hospital obstetrical patients that have been administered intravenous magnesium sulfate.

This test is only for Obstectric (OBGYN) Patients.

Collection Instructions

Specimen Collection: Blood


Container(s): 4.5 mL Mint Green Top (Lithium Heparin Gel) or 5.0 mL Gold Top (Serum Separator-SST Gel)

Preferred Volume to Collect: 4.5 mL

Minimum Volume to Collect: 1.0 mL

Neonate Volume to Collect: Not applicable

Capillary collect ok? Yes

Microtainer acceptable: Yes


Collection Instructions:

  • This test is only for Obstectric (OBGYN) Patients.

  • After collection, gently invert tube 8-10 times.
  • Specimen should be processed within 2 hours – See Processing Instructions.

Processing Instructions (Laboratory, Outpatient or Off-site collection)

Processed Specimen: Plasma or Serum

Centrifuge/Spin: Yes

Aliquot: Yes


Processing Instructions:

  • Plasma is preferred specimen type
  • Green Tube/Plasma: Centrifuge after collection within 2 hours.
  • Gold Tube/Serum: Allow blood to clot for 30 minutes in a vertical position and centrifuge within 1 hour.

Transport Temperature: Refrigerate

Specimen Transport Temperature


Specimen Stability

Ambient: 8 hours

Refrigerate: 72 hours

Frozen: aliquot plasma/serum for longer storage

Laboratory Retention: 72 hours

Test Frequency

Available 24 hours, usual TAT 1 day.

Reference Range

4.8 – 8.0 mg/dL Therapeutic

8.0 – 12.0 mg/dL Loss of Deep Tendon Reflexes

10.0 – 12.0 mg/dL Somnolence

12.0 -16.0 mg/dL Respiratory difficulty/depression

15.0 -17.0 mg/dL muscular paralysis

> 18.0 mg/dL altered cardiac conduction


Laboratory Critical Values Table

Performing Department


Performing Department Laboratory Location

Spectrum Health Regional Laboratory, Grand Rapids, MI
Spectrum Health Big Rapids Laboratory, Big Rapids, MI
Spectrum Health Blodgett Laboratory, Grand Rapids, MI
Spectrum Health Gerber Laboratory, Fremont, MI
Spectrum Health Kelsey Laboratory, Lakeview, MI
Spectrum Health Ludington Laboratory, Ludington, MI
Spectrum Health Pennock Laboratory, Hastings, MI
Spectrum Health Reed City Laboratory, Reed City, MI
Spectrum Health United Laboratory, Greenville, MI
Spectrum Health Zeeland Laboratory, Zeeland, MI





CDM Code


Epic Test ID


Interface Order Alias


Additional Information

PolicyTech Procedure Reference #8530: Magnesium Sulfate Infusion in the Obstetrical Patient

Reviewed Date