Media playback is unsupported on your device Media caption Finding out more about 'all the shaky-shake stuff'

"Be careful what you wish for, lest it come true," sums up a good lesson about life.

Don't wish it away and if you get things you desire, there may be unpleasant circumstances.

For James McGleenan, 11, that old Chinese proverb worked in his favour as a personal wish recently came true at Belfast City Hospital.

James is a haemophilia patient and was curious about what happened to his blood after it was taken by doctors.

So staff invited him to become a member of Harvey's Gang - a national initiative which demystifies what goes on in hospital by allowing children behind the scenes.

Image caption James McGleenan takes blood from his doctor, Gary Benson

They are allowed to touch, to ask questions and even to do things for themselves.

Wearing his own white coat, James and his doctor, Dr Gary Benson, swapped places.

First, James extracted blood. The needle was inserted and the blood withdrawn into a bottle.

He learned that labels are important, as is bedside manner.

Dr Benson, a haemophilia consultant, guided James's hand and the needle.

"Pretend you are a plane coming into land. Go in a wee bit deeper, round the corner of the vein, that's it you are doing a great job," he said.

Harvey's Gang started with an idea at Worthing Hospital in Western Sussex NHS Trust.

In March 2013, a boy called Harvey was admitted and diagnosed with acute leukaemia.

Image caption James enjoyed the opportunity to find out what happened when doctors took his blood

He was inquisitive about his condition and especially about what happened to his blood after it left his body.

He was invited to the lab, wore a specially-made white coat, engaged with staff and, as they say, the rest is history.

Sadly Harvey died several months later and, in his memory, Harvey's Gang was born.

In Belfast, Nicola McCrea, a bio-medical scientist said the initiative is a healthy reminder that at the end of every blood sample under examination, there is a person.

"As bio-medical scientists we have very little interaction with the patient. So it is actually lovely to see the patient come into the lab and actually put a face to the sample," she said.

"It's also a reminder that at the end of every sample there is a patient waiting on a result."

James carried the blood sample to the lab where labels were checked and placed in the analyser machine.

Image caption Harvey's Gang: a child with leukaemia has helped demystify the doctor's world for other children

He was intrigued.

"It's just brilliant. I now know when you shake blood about it separates the platelets from the blood cells. I saw my own blood being analysed and a lot of things make sense now," he said.

As a haemophilia patient, James has to be careful of internal bleeding and cannot do contact sport.

James's father Conal says they are very protective of him.

"We give him a replacement factor to bring his factor levels up to a couple of per cent of what they should be," he said.

"We do this every other day via injection that helps prevent little spontaneous bleeds that may happen in his everyday life."

"If he didn't get his treatment he could continue to bleed internally which could lead to serious joint damage and arthritis. If he fell or was in an accident and didn't have his treatment he could eventually die."

Dr Benson said Harvey's initiative was excellent for everyone involved.

"It lets people like James know what we, the medics, are doing. Also, monitoring his blood like we do ensures he is on the right medication.

"The staff has known James since he was born and since they did the cord blood test. I'd say we are all as excited as James is."

The tour ended and James was given a Harvey's Gang goody bag.

He didn't stop smiling, and neither did the staff.

See Marie Louise's full report on Tuesday's BBC Newsline at 18:30