What is the critical range for magnesium?

• A. 0.5-2.0 mg/dL
• B. 1-4.7 mg/dL
• C. 2-6 mg/dL
• D. 1.5-3.5 mg/dL

Answer: (B)

Critical values are results that require immediate action and notification of the clinician. For magnesium, the thresholds commonly used to trigger urgent reporting are around 1.0 mg/dL on the low side and about 4.7 mg/dL on the high side. Therefore, the range that defines the boundary for noncritical results is roughly 1 to 4.7 mg/dL; values outside this interval are considered critical and should be communicated promptly. This makes 1–4.7 mg/dL the best choice, as it reflects the standard reporting window labs use to determine when magnesium results become critical.