Collection of capillary blood for the measurement of retinol binding protein (RBP), ferritin, soluble Transferrin Receptor (sTfR), c-reactive Protein (CRP) and alpha-1-glycoprotein (AGP)

For the detection of Vitamin A and iron deficiency it is possible to measure certain proteins (RBP for Vitamin A deficiency, Ferritin and sTfR for iron deficiency) with a very sensitive and inexpensive Sandwich ELISA technique (Erhardt JG et. al. 2004). Already 16 ul plasma are sufficient to do a double measurement of these 3 proteins together with indicators of the infectious status (CRP for acute infections and AGP for chronic infections). The infectious status is very often interesting by itself but can also be used to correct the indicators for the Vitamin A and iron status which are influenced by infection. A simple finger prick is usually sufficient to collect enough blood. To increase the blood volume warming the finger, using more efficient lancets or adding vaseline to the puncture site can be helpful procedures. The following pictures show two different tubes which are used for the collection of capillary blood samples.

Approximately 60 ul whole blood

After centrifugation

This amount of plasma (a little bit more than 20 ul) is sufficient to measure all 5 proteins.

This blood tube contains a Gel separator to separate the erythrocytes from the serum fraction.

After centrifugation the tube can directly be frozen or send to the lab. There is no need to pipette in the field the plasma into another tube.

Extensive tests at the CDC in Atlanta have shown that proteins in plasma are stable at room temperature for one week. Therefore it is possible to collect plasma samples in the field without freezing and sending them not on dry ice to the lab.