Not Every Drop of Blood Is Identical
As our program moves forward in developing a point-of-care, rapid diagnostic test for detecting liver enzymes, AST and ALT, in indicating abnormal liver function, one important objective of our device is that it should rely on small amounts of blood. Due to limited specialized staff and venipuncture equipment, tests that use fingerprick blood would be most practical and inexpensive for the Zanzibar medical community. However, according to a recent study exploring the variations in cellular components in drops of blood, results from fingerprick blood tests may not be as accurate as results from tests that use blood from traditional methods of venipuncture; that is inserting a needle into an arm vein.
The study, which was conducted at Rice University, shows that different drops of blood in each patient had considerable fluctuations in blood parameters. Specifically, the average percent coefficient of variation (CV) for consecutive drops of fingerprick blood was higher by up to 3.4 times for hemoglobin, 5.7 times for WBC count, 3 times for lymphocyte count, 7.7 times for granulocyte count, and 4 times for platelets than in venous controls measured using a hematology analyzer.
To be clear, the data presented in this study is not invalidating the reliability of fingerprick blood measurements, but is only suggests caution in that by using fingerprick measurements, one be will sacrificing some accuracy in blood test results. The study has also stated that in order to get results as accurate as those attained from the traditional venipuncture method, using six to nine drops of blood is recommended. A single drop of blood, which is roughly 35 μL of blood, is typically used in fingerprick tests. Six to nine drops of blood occupies a much larger volume that ranges from 210 to 315 μL.
In relating these findings to the use of blood volume in our rapid diagnostic device, this is something we must consider and decide on in designing our rapid diagnostic device for liver function. By using a very small amount of blood, we will risk a decrease in the accuracy of our device. On the other hand, by using a large volume of blood, we will be maintaining accuracy, but may be compromising the ease of using the device. Therefore, we strive to find an optimal volume of blood that not only provides the convenience of usage but also yields the most accurate results as possible.
Reference: http://ajcp.oxfordjournals.org/content/144/6/885.abstract