What is the maximum puncture depth for a premature infant?

For premature infants, the maximum puncture depth during heel stick procedures is 0.85 mm. This restriction exists because premature neonates have significantly less subcutaneous tissue and a much thinner heel pad than full-term infants or older children. Exceeding 0.85 mm risks penetrating the calcaneal bone, which can cause osteomyelitis or calcaneous damage — serious complications in an already fragile population. By contrast, full-term neonates allow a maximum depth of 2.0 mm, and older pediatric patients may tolerate slightly deeper punctures depending on the site. The 2.0 mm option and 2.5 mm option reflect limits appropriate for full-term neonates and older children, not premature infants. The option showing only 'mm' without a value is clearly incomplete and cannot be correct. Knowing device-specific depth limits is fundamental to capillary blood collection safety, and clinical lancets used for premature neonates are specifically engineered not to exceed the 0.85 mm threshold to protect bone integrity. This concept is tested frequently in phlebotomy and nursing fundamentals courses because the premature infant is the most vulnerable patient population in whom heel stick errors carry the gravest consequences.