The average weight of a newborn in the United States is about 7.5 pounds (3.5 kg). Given their limited body mass, guidelines were established to limit the volume of blood drawn for diagnostic testing.
The essential guideline for traditional blood sampling, according to Seattle Children’s Hospital, is that no more than 2.5% of the total blood volume (TBV) of an infant can be drawn at one time. In addition, no more than 5% can be taken within a 30-day period. These standards vary by country.
Infants with a bodyweight of 6.6 pounds, for example, have a total blood volume of 240 ml. Therefore, the maximum amount of blood that can be drawn for analysis may not exceed 6ml. And, no more than 12 ml should be taken in a 30-day period.
This limitation becomes a problem for conditions that might normally require continual evaluation.
Infant Blood Screening
Blood screening of newborns is conducted to detect the presence (or absence) of a number of disorders. According to the U.S. National Library of Medicine, conditions such as metabolism disorders, cystic fibrosis, HIV, sickle cell disease, and more must be determined early in order to treat properly.
A 20µl sample is smaller than 1/10,000 of the size of the 6ml sample. Most importantly, these capillary blood samples can be dried, held, transported, and stored without refrigeration or special handling and do not deteriorate the same way as whole blood samples.
Drawing a tiny blood droplet is less stressful for the infant.
Samples may be taken as often as needed for continual observation of the progress of specific conditions and treatments.
More frequent, less stressful sample collections can lead to better overall diagnoses and proper treatment sooner.
Low blood volume patients, particularly infants, can be subjected to more frequent sampling at less risk than with traditional venous blood collection.
More frequent, low volume samplings are less painful and even allow for home blood sampling of infants. In some cases, the infant may be allowed to go home sooner because the child’s ongoing condition can be analyzed remotely.