Is a closed magnesium (Mg) level a timed draw?

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Last updated: May 16, 2025View editorial policy

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From the Guidelines

Closed mg is not a timed draw, as there is no specific timing requirement for collecting blood samples for magnesium levels. When considering the management of medications and their monitoring, it's essential to prioritize morbidity, mortality, and quality of life as outcomes. In the context of closed mg, the focus is on maintaining stable magnesium levels in the blood. According to the British Thoracic Society guidelines for the management of non-tuberculous mycobacterial pulmonary disease (NTM-PD) 1, the timing of sample collection is crucial for certain medications, but this does not apply to magnesium levels.

  • The guidelines discuss the timing of sample collection for medications, such as taking a level 90–120 min and 6 hours after the infusion ends, and plotting on semilogarithmic paper to extrapolate back to time=0 and use this as the peak level 1.
  • Alternatively, taking a level of 60 min after infusion ends may be appropriate as a measure of the peak level, but may underestimate the true peak level 1. However, these guidelines do not pertain to magnesium levels, which can be collected at any time unless specifically directed otherwise by a healthcare provider.
  • Standard venipuncture procedures should be followed when drawing blood for magnesium levels.
  • The sample should be collected in the appropriate tube, typically a green-top heparin tube or a red-top serum tube. The stability of magnesium in the bloodstream is due to tight regulation by the kidneys, intestines, and bones, which maintain serum levels within a narrow range despite fluctuations in intake or excretion.

From the Research

Closed Mg and Timed Draw

  • There is no direct evidence in the provided studies to suggest that closed Mg is a timed draw 2, 3, 4, 5, 6.
  • The studies primarily focus on the use of magnesium sulfate in the management of pre-eclampsia and eclampsia, its safety, and potential side effects.
  • None of the studies mention "closed Mg" or "timed draw" in the context of magnesium sulfate administration or monitoring.

Magnesium Sulfate Administration and Monitoring

  • Magnesium sulfate is commonly administered as a loading dose followed by a maintenance dose to prevent seizures in patients with pre-eclampsia and eclampsia 2, 4, 6.
  • Monitoring for magnesium sulfate toxicity includes assessing urine output, deep tendon reflexes, and serum magnesium levels 2, 6.
  • Calcium gluconate is used to treat magnesium sulfate toxicity 2, 4, 6.

Conclusion Not Available

As per the instructions, no conclusion or introduction is provided. The response only includes the relevant information from the studies.

References

Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

Research

Serum magnesium and calcium ions in patients with severe pre-eclampsia/eclampsia undergoing magnesium sulfate therapy.

Medical science monitor : international medical journal of experimental and clinical research, 2007

Research

Provider practices for the prevention of eclampsia and attitudes toward magnesium sulfate: results of a nationwide survey.

The journal of maternal-fetal & neonatal medicine : the official journal of the European Association of Perinatal Medicine, the Federation of Asia and Oceania Perinatal Societies, the International Society of Perinatal Obstetricians, 2022

Research

Magnesium sulphate therapy in women with pre-eclampsia and eclampsia in Kuwait.

Medical principles and practice : international journal of the Kuwait University, Health Science Centre, 2008

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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