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To the Editor.—
The International System of Units (SI) (240:1618, 1978) perpetuates one of the major shackles imposed by the laboratory man on his clinical colleagues—a Tower of Babel in normal enzyme levels. Each enzyme, however rarely used, has its own normal level that has to be memorized, or a call to the laboratory is required. If different substrates are used for the same enzyme, then there are many normal levels for the same enzyme, all in SI units. The patient-related problems are numerous. Normal levels for a laboratory may change. Last month I sent a patient to an emergency room for an amylase reading; I knew the normal level to be 200. The value was 148, but one week later, I found that the normal level had been changed the week before to 28—rather devastating. When normal levels change, reading old charts is tougher than reading cuneiform—one needs to
Langdon DE. SI Units and Enzyme Levels. JAMA. 1979;241(12):1229. doi:10.1001/jama.1979.03290380013011