SAN FRANCISCO — Get ready for a big fight over the words “micro” and “nano.”

Palo Alto-based medical testing company Theranos Inc. launched a preemptive strike in a trademark spat with rival Becton Dickinson Co. on Monday. Theranos is asking for a declaratory judgment that its use of the name nanotainer for blood collection tubes doesn’t infringing upon Becton Dickinson’s trademark for microtainer.