Dear Iyke,
I truly wish it was as easy as that. Hospital based childhood nutritional assessments could theoretically reflect the situation in the community, but there so many factors that can bias the information that it cannot be relied upon. Here are a few of the problems I've seen with this data.
1) Even if you have people in the communities trained to detect children who are malnourished, not all of these people will be as active in referring the children. You may end up with more referrals from some communities simply because those trained screeners are more active.
2) Being farther away from a hospital increases the demands on the family taking their child to the hospital, so you may get a higher percentage of the cases from nearby communities and a lower percentage from communities farther away. The nutritional situation may be different in the more distant communities.
3) Even if the care for malnourished children provided by the hospital is free, there is an opportunity cost for the caregivers in time and travel. The poorest families, who are often the most likely to have malnourished children, are sometimes the least likely to take their children for treatment because they cannot stop working long enough or don't have money for the transportation. This is especially important in rural areas were distances may be longer and transportation relatively more expensive.
4) If the supply pipeline is irregular, changes in admissions are often more reflective of the breaks in supply than from changes in actual prevalence.
5) Depending on where you are, one type of malnutrition (kwashiorkor or marasmus) may be considered serious and the other not, which may change the likelihood of whether or not parents bring children to the hospital.
6) Some malnutrition may be linked to illness. The parents may bring to hospital children with a fever, but not think to bring a child that is malnourished but appears to be otherwise healthy. This could give you the idea that malnutrition is mostly due to illness, when perhaps there are more cases caused by local childcare practices.
I am sure some of our colleagues could come up with other factors that could affect the hospital-based data.
For the survey parameters, as Mark suggested, testing for bi-pedal edema should be included. Sometimes people include head circumference for small children, but I don't see this as often.
Good luck