Haemorrhage responsive to vitamin K in a 6-week-old infant

A 6-week-old breast-fed infant presented with vomiting, jaundice, and irritability. Haemorrhage occurred after lumbar puncture, and a coagulation abnormality which responded to vitamin K was found. It would seem prudent to estimate the prothrombin time before invasive procedures in breast-fed infants of this age, or to give vitamin K to such infants when doubt exists about previous vitamin K administration.