Light therapy helps the baby's body process the excess bilirubin
Health workers should no longer rely on instincts alone to judge the severity of jaundice in a newborn baby, guidance from the health watchdog recommends.
NICE wants blood tests for all newborns with suspected jaundice, a common and usually harmless condition but which can in rare cases be fatal.
The risk of kernicterus, a form of brain damage, can be averted completely if serious jaundice is spotted early.
The guidelines include specific advice on when to start and stop treatment.
Jaundice is prevalent among newborns - around 80% of premature babies and 60% of full-term babies develop it within the first week of life.
The condition is caused by high levels of bilirubin - a waste product created by the breakdown of red blood cells. The baby's immature liver often struggles to remove this substance from the body, so it starts to build up.
Deposited in the skin and eyes, it causes the yellow colour from which jaundice gets its name, but in serious cases it can damage the brain.
The condition, kernicterus, can cause long-term problems such as cerebral palsy and hearing loss, and in a handful of cases can be fatal. It is rare, but thought to be on the increase, affecting up to 12 babies a year in the UK.
But because for the vast majority of babies jaundice is entirely harmless, there has been some uncertainty as to when and how to treat it.
Warning symptoms and signs
Severe jaundice - particularly in the first 24 hours of life
Abnormal muscle tone
Spasms in the head, neck and spine
Health workers tend to rely on the appearance of the baby alone to diagnose the severity of a case of jaundice, but the National Institute for Health and Clinical Excellence (NICE) notes that this can be problematic, particularly when it comes to babies with darker skin tones.
The watchdog says all babies should be checked for jaundice regularly in the first 72 hours and, when the condition is suspected, tests to ascertain bilirubin level should be carried out every six hours.
Light therapy should then be used for babies with jaundice above a certain threshold, with treatment intensifying to include blood transfusion for the worst affected.
Dr Fergus Macbeth, director of the Centre for Clinical Practice at NICE, said: "The majority of babies will develop jaundice in their first week of life and it will be generally harmless in most cases.
"Although the condition does have the potential to become serious, it can usually be easily treated with timely and appropriate medical care. This guideline will ensure that happens."
Dr Janet Rennie, consultant neonatologist at University College Hospital London, said: "These recommendations should ensure that babies who have factors associated with an increased likelihood of developing significant jaundice are identified earlier so they receive prompt effective and appropriate treatment, directed at preventing permanent damage."
The Royal College of Midwives welcomed the new guidelines.
"Most cases of jaundice in newborns will be harmless, but a very small number could potentially be dangerous to the baby," said the RCM's education and professional development advisor Gail Johnson.
"We would advise any new parents who may be concerned about possible jaundice in their child to contact their midwife or doctor straight away."