Dylan Edwards (asker) Nov 14, 2011:

I suppose each column in an Excel file of this kind represents a different question, and each row contains a different person's answer.

ENA isn't used in this way anywhere else in the file, and it still looks to me like the indefinite article.
It says "ENA 10% ..." - the use of the indefinite article suggests to me that they mean a 10% portion, as thomgeor80 suggests.

A couple of rows further down, it's the same phrase with ENA omitted - "10% ..." - but I think it means the same thing.

Dave Bindon Nov 9, 2011:

Ahhh.....! I'd been wondering whether or not you had the questionnaire. My guess is that the answers are in reply to a "Which of the following 10 statements is correct?" question, and this statement happens to be option (one).

Dylan Edwards (asker) Nov 9, 2011:

Well, it's typical of jobs of this kind: I don't have the question, or I can't easily find the question. I've worded it (deliberately vaguely) as follows: 10% AUSTRALIA ANTIGEN NEGATIVE.
I sent it to the client with my comment, leaving the interpretation to them.

D. Harvatis Nov 9, 2011:

You're probably right with your last guess. Another, less likely option is that the HBsAg becomes negative with a 10% dose of the drug. Could you provide some of the questions to which this is a possible answer?