Which patient group is commonly considered to require cysteine provision in PN?

• A. Preterm infants
• B. Term infants
• C. Adults
• D. Elderly

Answer: (A)

Preterm infants commonly require cysteine in PN because they cannot produce enough of this sulfur-containing amino acid on their own. Their immature transsulfuration pathway and limited hepatic capacity mean they rely on dietary cysteine to meet needs for growth and for making glutathione, an essential antioxidant. This makes cysteine a conditionally essential nutrient for them, so PN formulations are typically supplemented with cysteine to prevent deficiency and support development.

Term infants, adults, and the elderly generally have more mature metabolism and can synthesize sufficient cysteine or obtain it adequately from diet, so cysteine provision in PN is not routinely required for these groups.