Which of the following can cause false negatives in newborn screening tests?

• A. Heat exposure
• B. Blood transfusions
• C. Improper sample collection
• D. Maternal medications

Answer: (B)

Blood transfusions can lead to false negatives in newborn screening tests primarily because they may dilute or replace the infant's blood with that of the donor, which alters the biochemical markers that the screening tests are designed to detect. If an infant has received a blood transfusion shortly before the screening, it might mask underlying metabolic conditions or inherited disorders by providing a transfusion of 'normal' values from the donor's blood.

For example, in the case of metabolic disorders such as phenylketonuria (PKU) or congenital hypothyroidism, the screening tests rely on the presence of specific metabolites or hormones in the newborn's blood. If a transfusion has occurred, it is possible that the levels of these metabolites may not accurately reflect the infant's true metabolic state, leading to a false negative result.

Improper sample collection can also lead to inaccurate results, but it typically would not specifically cause false negatives in the same direct manner as a blood transfusion does. Other factors like heat exposure and maternal medications may influence the testing process or results but are less likely to directly result in false negative results compared to blood transfusions.