Corrected calcium

• Corrected calcium = 0.02 x (40- albumin level) + calcium level
  • Units: calcium in mmol/L; albumin in g/L

Example:
Serum calcium 1.98 mmol/L
Serum albumin 23 g/L

1⃣ 
Normal albumin - current albumin
40 - 23 = 17

2⃣ 
1⃣ x 2 ÷ 100 
17 x 2 ÷ 100 = 0.34

3⃣ 
2⃣ + serum calcium level
0.34 + 1.98

Answer: Corrected serum calcium = 2.32 mmol/L

Calculation of potassium deficit

• Potassium deficit (g) = [(4 – current potassium level) × 0.4 × bodyweight]/13.4]
  • Unit: potassium in mmol/L
• Clinical significance: for fast correction of potassium in hypokalaemia cases

Anion gap

• Anion Gap = (Na⁺ + K⁺) – (Cl ^–+ HCO₃)
  • Units: all in mmol/L
  • Normal range: 8 – 16
• Clinical significance: to differentiate between high anion gap metabolic acidosis (HAGMA) and normal anion gap metabolic acidosis (NAGMA)

Calculated plasma osmolality

• Calculated plasma osmolality = (2 x Na⁺ ) + Urea + Glucose
  • Units: all in mmol/L
• Clinical significance: part of the diagnostic criteria for Hyperglycaemic hyperosmolar state (HHS)
  • Severe dehydration
  • Marked hyperglycaemia (plasma glucose >30 mmol/L)
  • Serum osmolality >320 mOsm/kg