Errors based on units of measure

Abstract

My narrative deals with an error avoided (which is no less instructive than an error made) that proves that physicians and nurses should be familiar with units of measure. The grandmother of a student nurse of mine was under calcium supplementation and discontinuous vitamin D3 therapy for a moderate, asymptomatic hypocalcaemia. She had had difficult relationships with physicians because of the postsurgical cause of her hypoparathyroidism. So, once her grandson became a registered nurse, he managed her calcaemia himself, consulting me about possible therapeutic adjustments. Calcaemia was always measured at the same laboratory, where another grandson worked. For a long time he regularly reported that calcaemia was normal at values of 8·6 to 9·1. Then one day, he called to tell me that his grandmother was asthenic. I recommended checking her calcaemia. After having talked with the laboratory, he called me at home, sounding agitated: “Professor, I have finally found you. I am at my grandmother’s. She is still asthenic, but also has the ’flu. My cousin is out of town and one of his colleagues at the laboratory tells me the calcaemia is at 4·83. My grandmother refuses to go to the hospital. I’ve got saline and calcium gluconate infusions here, and want to check with you if the dose suggested by your colleague is OK”. “Wait a moment, I’m coming”, I said, wondering how calcaemia could drop by 50% in a matter of a few weeks in a lady compliant to therapy. 10 minutes later, I was there. The lady had no signs of hypocalcaemia and no oedema that could have suggested albuminuria and consequently falsely low concentrations of calcium in the blood. I called the laboratory and asked the clinical chemist to double-check the results. “Yes, calcaemia is 4·83”. “4·83 what?”, I replied. No answer. “Please, tell me the unit of measure and normal range you are using”. This time, the response was quick: “4·83 mEq/L, with a reference range of 4·24 to 5·20”. The mystery was solved! The chemist acknowledged that the laboratory had recently changed its kit, and values were now given in mEq/L instead of mg/dL. Almost in tears, the nurse said he had been ready to infuse calcium had he not found me, so terrible was his recollection of a patient with tetany and calcaemia of 5. Since this incident, my first session of problem-based learning for students and nurses deals with this story. Year after year, I am told it was one of the most useful.