A toddler died after NHS errors meant doctors missed an opportunity to diagnose the illness that led to his death, an inquest has heard.

Samuel Weithers died in November 2010, aged just 18 months old, of heart disease caused by a rare genetic disorder.

South London Coroner's Court heard on Thursday doctors who treated Samuel, of Norbury, in the run-up to his death were unaware he suffered from a glucose deficiency - known as G6PD deficiency - despite it being listed in his medical records.

Paediatricians at Croydon University Hospital (CUH) and Samuel's GP at Norbury Medical Practice told the court they would have treated him differently had they known of the deficiency.

Samuel was misdiagnosed with and treated for tonsillitis after his concerned parents Mark and Annette, of Courtland Avenue, took him to hospital on November 17, having been referred by his GP.

He returned to hospital on November 28, his condition having worsened, and was found to be severely anaemic and probably in heart failure.

Theo Fenton, a consultant paediatrician at CUH, said the severity of Samuel's anaemia was a "one in 500,000 event".

Despite treatment including a blood transfusion, he fell further ill and died at 9am the next day.

Ben Bradley, the family's lawyer, questioned doctors' decision not to administer a diuretic when he received a blood transfusion and criticised the hospital's failure to inform his family of his G6PD deficiency.

The court heard Samuel's GP and his parents should have received notice of his G6PD deficiency when it was diagnosed shortly after birth, allowing them to inform doctors treating him, but neither were.

John Chang, the paediatrician who initially diagnosed the deficiency, accepted responsibility for the "administrative failure" and assured the family procedures had been changed so the mistake would not be repeated.

Coroner Roy Palmer, recording a narrative verdict, said Samuel's heart disease had probably been present for weeks before his death and that doctors' unawareness of his G6PD deficiency had resulted in "a lost opportunity to investigate the cause of his symptoms".

He ruled it was impossible to say whether using a diuretic during Samuel's blood transfusion - rather than just after - would have helped to prevent his death.