What is a common factor seen in the clinical assessment of infants with probable jaundice and lethargy?

In the context of infants presenting with probable jaundice and lethargy, elevated serum ammonia is a significant concern. The presence of jaundice indicates an accumulation of bilirubin, which can disrupt normal liver function. In cases where the liver is not functioning properly, such as in certain metabolic disorders or liver dysfunctions, ammonia levels can rise. This is because the liver plays a crucial role in detoxifying ammonia, converting it into urea for excretion. Elevated serum ammonia can lead to further neurological issues and lethargy, which are particularly critical in infants whose physiological responses to hyperammonemia may manifest as decreased activity or lethargy.

The other options, while they may be relevant in different contexts, do not directly correlate with the specific clinical scenario involving jaundice and lethargy in infants. Elevated blood pressure is less commonly associated with neonatal jaundice, while a high heart rate may occur in various conditions but is not specific to jaundice or lethargy. Additionally, increased appetite is typically not expected in infants who are lethargic, as lethargy often results in decreased feeding behavior. Thus, elevated serum ammonia stands out as a key factor to consider in this clinical assessment.