the detection of Vitamin A and iron deficiency it is possible
to measure certain proteins in blood (RBP for Vitamin A deficiency,
Ferritin and sTfR for iron deficiency) with a sensitive and
inexpensive Sandwich ELISA technique (Erhardt JG et. al. 2004).
It can also be easily combined with the measurement of
CRP and AGP as indicators for the early and late stage of an infection. The
infectious status can be of interest by itself but also be
used to correct RBP and ferritin which are influenced by infection. More information on Vit. A and Iron
can be found in these extensive and relatively new reviews and for surveys in general the WHO Micronutrient survey manual might be of use (including the information of the two other documents in a more compact form).
The combined Sandwich
ELISA technique needs some experience and there are problems with
the availability of the antibodies but the advantage is that the 5
proteins can be measured for 5 USD/sample (in average 1 USD per
protein) with a high throughput procedure in bigger sample sizes. As material serum from venous or capillary sampling
can be used and already 25 ul are sufficient to do a double measurement
of these 5 proteins. Therefore a finger or heel prick is usually
sufficient to get enough blood for doing these measurements. The
best material for the measurement of the proteins is serum. Heparin
plasma usually forms cryoprecipitates after a freeze/thaw cycle which
can block the tips of the pipettor and EDTA plasma can have
problems with the stability of sTfR after freeze/thaw cycles.