This is what the latest edition of the AAMT BOS has to say about percent.
quote:
percent (%)
Note that percent is a single word.Do not use the abbreviation pct. except in tables. Use % or percent.
50% or fifty percent, not 50 pct.
Use the symbol % after a numeral. Do not space between the numeral and the symbol.
13% monos, 1% bands
She has had a 10% increase in weight since her last visit.
MCHC 34%
10% solution
Use numerals for the number preceding %.
50%, not fifty%
When the number is written out, as at the beginning of a sentence, write out percent.
Fifty percent of the patients were given a placebo.
According to the SI (International System of Units), it is common and acceptable for percents to be expressed as a fraction of one. MT experience would indicate that is is more common and acceptable for percent to be dropped in dictation (and hence in transcription). Use the expression dictated; do not convert.
polys 58% or polys 0.58 or polys 58
MCHC 34% or MCHC 0.34 or MCHC 34
range
In a range of values, repeat % (or percent) with each value.
Values ranged from 13% to 18%.
not Values ranged from 13 to 18%.
Fifty percent to eighty percent.
not Fifty to eighty percent.
subject-verb agreement
Percent of takes a singular verb when the word following of is singular, a plural verb when the word following of is plural.
Ninety percent of the body was burned.
Forty percent of the patients were in the control group.
Percent takes a singular verb when it stands alone (not followed by of).
Fifty percent is adequate.
See subject-verb agreement.
less than 1 percent
When the amount is less than 1 percent, place a zero before the decimal.
0.5% not .5%
With whole numbers, avoid following the number by a decimal point and a zero, since such terms are easily misread. The decimal point and zero may be used if it is important to express exactness. Use it if dictated.
5%, not 5.0%
Use decimals, not fractions, with percents.
0.5%, not 1/2%
percentage point
Percentage point is not the same as percent. Thus, a decrease from 10 percent to 5 percent is a decrease of 5 percentage points. It represents a decrease of 50 percent, not a decrease of 5 percent.
percentile
Probability distribution. If a boy's height is at the "50th percentile," he is at the same height as 50% of the boys his age.
Hmmmmm....how odd. I just noticed that they're violating their own guidelines there with the text following "percentage point" (by not using symbols following the numerals)!!! Ah well, nobody's perfect! LOL (I think I'll drop them an email about that!)
deeduze, I think you're thinking of the old grammar rules about writing out numbers one through nine, and using numerals for 10 and above. (This is not the recommendation anymore, by the way, at least as far as the AAMT is concerned!)
cats, I hope this helps you out a little. Personally, I pretty much always use a numeral with the symbol unless it is at the beginning of a sentence and the sentence can't be recast to move the number away from the being the first word.
Oh shoot...I just re-read your post to discover that you had already checked the BOS. DUH! Ah well, I took the time to type it all out, I'm not going to erase it now! 
