English to Spanish Medical Medical (general)

In a consent form for a genetic study, the term "bajo llave" was not accepted by customer in the phrase below as a translation of 'locked' :

"Dr. XXX will keep locked separately a code sheet which links the sample code number with your name and hospital number."

Maybe 'locked' here means 'abrochado'? Basically the code sheet will be kept safe and private. Pls share your suggestions, thx