The word is derived from the letters that make up the word.
L is for light, a for amplification by, s for stimulated, e for emission of, and r for radiation.
Electroencephalogram or a brain wave test that helps determine the presence of seizures. The blood test, cbc, is a complete blood count that examines red and white cells and determines if anemia is present. Taking a medicine prn means taking it as needed. If the medicine needs to be taken immediately then the word stat is used. Taking it p.o. means by mouth.