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Test Findings




    • Look For

    • Serum magnesium <0.7 mmol/L.


    • Causes of Hypomagnesaemia

    • Reduced intake - malnutrition, TPN
    • Urinary loss - acute tubular necrosis (polyuric phase), postobstructive diuresis, loop / thiazide diuretics, ACE inhibitors, renal tubular acidosis, aminoglycoside toxicity, hypercalcaemia, genetic tubular defects
    • GI loss - diarrhoea, laxative abuse, malabsorption, vomiting, NG aspirates, GI fistula, short bowel syndrome, long-term PPI use
    • Compartmental shift - refeeding syndrome, hyperparathyroidism, hyperthyroidism, acute pancreatitis, hungry bone syndrome

Clinical Features

    • Signs and Symptoms

      Only occur in the presence of resultant biochemical abnormalities
    • Hypocalcaemia - hyperreflexia, tetany, seizures, heart failure
    • Hypokalaemia - weakness, hypotonicity, depression, constipation, ileus
    • ECG Changes

    • Long QTc → torsade de pointes
    • Atrial or ventricular ectopics
    • Atrial fibrillation
    • Ventricular arrhythmias
    • Hypokalaemia - ST depression, prolonged QT interval, T wave flattening or inversion, prominent U wave
    • Associated Lab Abnormalities

    • Hypokalaemia
    • Hypocalcaemia
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