Question

A 56-year-old female was evaluated for cardiac arrhythmia. Her current medications included digoxin which was prescribed following a myocardial infract 4 years ago and hydrochlorothiazide (a diuretic) which was prescribed 2 years ago to treat recurrent bouts of edema.

Laboratory results were as follows: Na: 145 mmol/L K: 3.0 mmol/L Cl: 100 mmol/L HCO3: 25 mmol/L Mg: 0.4 mmol/L Ionized Ca: 1.0 mmol/L Digoxin: 1.4 ng/mL (therapeutic range: 0.5 – 2.2)

1. Calculate the anion gap. Is the anion gap normal? Explain why or why not.

2. List at least two functions of magnesium ions.

3. Explain the most likely reason for the magnesium level seen in this patient?

4. Explain the most likely reason for the calcium level in this patient?

Answer 1

In the present case study, a 56-year old female was evaluated for cardiac arrhythmia.

In the lab results:

* Na: 145 mmol/L

*K: 3.0 mmol/L

*Cl: 100 mmol/L

*HCO3: 25 mmol/L

1. The equation used to calculate the anion gap is: (Na+K) - (Cl + HCO3)

Thus we can calculate by applying the lab values to the equation

=(145+3) - (100+25)

=(148) - (125)

=23 mmol/L

The reference range for the anion gap in a healthy person is 10-20 mmol/L

The main causes of an increased anion gap due to a metabolic acidosis that maybe includes :

Methanol intoxication, Uremia, Diabetic ketoacidosis, Paraldehyde intoxication, Infection, Lactic acidosis, Ethylene glycol intoxication, and Salicylate intoxication.

Thus we can say that the patient is not healthy

2. Magnesium is a:

- divalent anion which complexes to organic phosphates and nucleic acids

- essential for effective aerobic and anaerobic metabolism

- binds things more strongly than calcium but is not as flexible in its ionic state.

3. Here in the present case study, the patient is evaluated for arrhythmias. The normal reference range of magnesium is 0.6-1.1 mmol/L. Here the patient lab results are showing low magnesium levels. The patient is taking hydrochlorothiazide for treating the bouts of oedema for the past 2 years ago. It is a diuretic coming under the group of thiazides. One of the main side effects of the thiazide diuretics is excreting the magnesium in high amount. This may lead to hypomagnesaemia and arrhythmias.

4. In the present case study, the patient lab value is showing the calcium range is 1.0mmol/L. The normal calcium range is 2.1 - 2.6mmol/L. Maybe the patient is suffering from chronic kidney disease and results in increased excretion of calcium and results in hypocalcemia.