For magnesium testing, which statement is true about preanalytical handling?

• A. Hemolysis can cause falsely increased magnesium
• B. Use EDTA tubes
• C. Use citrate tubes
• D. Hemolysis has no effect on magnesium

Answer: (D)

Magnesium testing is highly sensitive to preanalytical handling because magnesium is largely an intracellular ion. If cells lyse during collection or processing (hemolysis), magnesium leaks into the serum/plasma, leading to a falsely elevated measurement. Using anticoagulants like EDTA or citrate is not appropriate for Mg testing because they bind divalent cations such as Mg2+, which can distort the result. Therefore, samples should be collected in proper tubes (e.g., serum or heparinized plasma) and kept free from hemolysis. The idea that hemolysis has no effect is not correct; hemolysis can cause a falsely increased magnesium result.