A serum potassium level of less than 3.5 millimoles per liter (mmol/L) may be considered low; the normal range is 3.6-5.2 mmol/L) Additional electrolyte levels such as calcium, glucose, magnesium and phosphorous may be checked at this time.  A blood assay may also include the blood urea nitrogen (BUN) and creatinine levels, which are indicators of kidney function. Patients who are taking digitalis also need their digoxin level checked as this medication affects heart rhythm. This will monitor the heart’s functioning for signs of damage or other problems. The doctor may have to shave parts of your skin if you have a lot of hair, and she will place 12 electrical leads on your arms, chest and legs. Each lead transmits electrical information about the heart to a monitor for 5 to 10 minutes. The patient should remain as still as possible and it may be necessary to repeat the ECG. Low potassium levels may also be related to low magnesium levels. This could prolong intervals on the EKG and could lead to Torsades de Pointes.

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Write a summary of the previous text in Vietnamese:
Kiểm tra nồng độ kali. Kiểm tra điện tâm đồ (ECG hoặc EKG).