Medical Surgical Labs Electrolytes Top Tested #2


Which sign or symptom would correlate with a magnesium level of 0.9?


  1. Torsades de Pointes
    • Rationale:

      This answer is correct because Torsades de Pointes is a type of ventricular tachycardia. It is caused by low magnesium. Low magnesium can cause QT prolongation. QT prolongation causes rapid heart beats that can trigger death.

  2. Trousseau's sign
    • Rationale:

      This answer is not correct because Trousseau’s sign is apparent with low calcium. Calcium levels should be between 9 – 10.5 mEq/L.

  3. Hyporeflexia
    • Rationale:

      This answer is not correct because hyporeflexia occurs with high magnesium levels: levels over 2.1 mEq/L.

  4. Decreased deep tendon reflexes
    • Rationale:

      This answer is not correct because decreased deep tendon reflexes are a sign of high magnesium: Levels over 2.1 mEq/L.


Magnesium levels should be between 1.3 -2.1 mEq/L. Levels below 1.3 can cause lethal heart rhythms.


Learning Outcomes

Magnesium is a mineral required for the body to contract and relax the muscles. It also regulates neurotransmitters throughout the brain and nervous system. Magnesium levels should be between 1.3-2.1 mEq/L. Levels below 1.3 are a medical emergency. Since magnesium is important for muscle contraction and relaxation, levels below 1.3 can cause fatal heart dysrhythmias. Torsades de Pointes is caused by a magnesium deficiency. Low serum magnesium causes QT prolongation which results in this deadly arrhythmia. High levels of magnesium produces greater relaxation of muscles, causing decreased deep tendon reflexes and hyporeflexia.

Test Taking Tip

Think “Magnesium Mellows”. The higher the value, the more mellow the muscle becomes. The lower the value, the less mellow the muscle becomes. Such as in Torsades de Pointes, where the heart beats chaotically and rapidly, potentially resulting in a fatal arrhythmia.

Video Rationale