Dear Anonymous 27728 / Étudiant / Tidiani Cisse,
I am not sure that I understand your question. I guess that you have a SAM case with WHZ < -3 and you want to work out what weight for the same height would give WHZ >= 2 and this becomes a "target weight". Is that correct?
If so then it should be quite easy to write an short R script which uses the functions and reference data in the zscorer package to do the calculations You could wrap that script up with Shiny so you could do the calculations in your web-browser.
The mechanics of the R script will be something like this:
## Load zscorer library
library(zscorer)
## Sex, weight, and height for a SAM case
sex = 1
height = 91
weight = 9.9
## Calculate WHZ for this case
getWGSR(sex = sex, firstPart = weight, secondPart = height, index = "wfh")
This gives:
[1] -3.633671
This is the WHZ for the specified case (i.e. sex = 1 (for male), height = 91, and weight = 9.9).
We now need to calculate what weight for the current height gives WHZ = 2
## Specify the objective function
objFun <- function(weight)
{
result <- getWGSR(sex = sex, firstPart = weight,
secondPart = height, index = "wfh") + 1.99
return(result)
}
## Find the weight that gives an answer closest to zero
uniroot(objFun, interval = c(weight, 25))$root
This gives:
[1] 11.23279
This is the target weight
We can check the result with the original height and the target weight:
getWGSR(sex = 1, firstPart = 11.23279, secondPart = 91, index = "wfh")
This gives:
[1] -1.990001
which, as we wanted it just above WHZ = -2.
This process assumes that no height is gained during treatment. This may not always be the case as children tend to grow quickly when their nutritional needs are met.
A simple alternative ... UNICEF guidelines have a 15% weight gain as a target. For the example child this would be:
9.9 * 1.15 = 11.385
We can check what that gives:
getWGSR(sex = 1, firstPart = 11.385, secondPart = 91, index = "wfh")
This gives:
[1] -1.813269
which is also a bit above WHZ < -2 giving some room for a little gain in height.
The 15% proportional weight gain apporach is simple to apply with a table or using a cheap and simple pocket calculator.
BTW ... The GMP target weight tables are for normal growth in weight and we expect / want accelerated growth in therapeutic feeding.
I hope this is useful.