Dear Anselimo,
If it is for assesment, I would register the exact MUAC and compare it to tables of MUAC-for-age, which will give you an idea of the deviation from the mdian for age.
There are still no defined MUAC cut-offs for children > 5 years, but if you take the ones for adults, you will overestimate malnutrition.
If it is to include children in a program, I tried a "simplified MUAC-for- height", based on an article published by Mei, Z., Grummer-Strawn, L. M., De Onis, M.,Yip, R.,in the WHO bulletin (vol 75, issue 4, 1997): "The development of a MUAC-for-height reference, including a comparison to other nutritional status screening indicators".
You do a kind of quack-stick with a mark at 110 - 120 - 130 - 145 cm, the child is standing next to the stick:
if his head is below 11,0 cm mark, admit him if MUAC is < 12,0 cm
if his head is between 110 & 120 cm mark, admit him if MUAC is < 14,0 cm
if his head is between 120 & 130 cm mark, admit him if MUAC is < 14,6 cm
if his head is between 130 & 145 cm mark, admit him if MUAC is < 15,2 cm
If he is taller than 145 cm, use adult’s criteria
These cut-off were choosen because they represent -3 z-score of the MUAC-for-height in the table.
This protocole is a trial, it has not been endorsed by anybody yet and need more field test, but I checked myself on Sudanese population and all children admitted were visibly wasted, so I don't think we overestimate too much malnutrition with these cut-offs.
hope this help
Pascale