A patient has calcium 1.9 mmol/L and albumin 25 g/L. Using a correction of 0.02 mmol/L for each g/L of albumin below 40, what is the corrected calcium?
Answer and explanation
Correct answer: A. 2.2 mmol/L, a value that lies within the normal range
- Step 1: Albumin is 15 g/L below 40, so add 15 times 0.02, which is 0.3 mmol/L. Step 2. The corrected calcium is 1.9 plus 0.3, which is 2.2 mmol/L. Answer: 2.2 mmol/L. Why not the others: Low albumin makes the total calcium look low, so correction is needed. Subtracting the correction gives the wrong direction. Adding too much gives a false hypercalcaemia.
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