A useful response says when more will be known instead of borrowing certainty from hope.

Under pressure to say something reassuring, it is tempting to offer a confidence you do not have. It works for a day, and then the thing is not fixed, and now the person has lost both the outcome and their trust in what you tell them. A date for the next information is worth more than a promise about the answer.

Say when you will know, and what you are doing in the meantime. Then keep that appointment, even if the update is that nothing has changed. People can sit with uncertainty far longer than with a reassurance that turned out to be a guess.