As part of a series of articles BBC News Online reporter Jane Elliott looks behind the scenes of the NHS.
Neil Leaver says the service is vital
This week we focus on how a machine to help transplant patients with drugs is saving the NHS millions.
Over the last two decades more than 2,000 patients have had heart and lung transplants at the Royal Brompton and Harefield NHS Trust.
More than half these patients are still surviving and experts say much of the success for this is down to effective anti-rejection drugs.
When a donor organ is implanted the body's natural defences would normally attack it in a similar manner to the way in which the body fights bacteria or foreign bodies.
Immunosuppressant drugs like Cyclosporine and Tacrolimus help the patient's body stave off rejection.
In the past, deciding how much of a particular drug a patient could need was a lengthy process with more than 1,000 patients currently needing medication.
But a new system to monitor drug levels is saving patients' time and the NHS about £250,000 each year - cash that can then be ploughed back into the hospital.
The money saved so far has been used to fund nine full-time nursing posts
Neil Leaver, clinical scientist and head of the trust's immunosuppression monitoring unit, said the service currently analysed about 26,000 patient blood samples each year.
He said the service was vital because if the concentration of a drug was too low, a patient could reject their transplant.
If the concentration was too high, a patient could suffer serious infection or other toxic side effects.
Now the service they offered patients was much faster, with consultants getting the results the day the patients visited hospital.
"This system is a lot more reliable," said Mr Leaver.
"If we have a drug and we add up all the carbon, nitrogen and atoms we get the weight, and then infuse that drug to get the peak.
"We were the first laboratory in the UK to introduce such a service and we are two or three years ahead of any laboratory in this particular niche market.
"It is difficult to quantify how successful it is, but the risk of rejection is less using this system.
"It is very difficult because we are not seeing the patients, but what we are doing is picking up the changes within patients a lot more quickly than we used to."
Jane Tiller, deputy head of the unit, added that the new service was of considerable benefit to patients.
"Our patients can come in the morning and after lunch they can go home knowing the doctors have seen their latest results.
"We can give them the information saying that this patient is OK or this patient is not OK.
"We are used by a reference laboratory by a lot of other hospitals and send their results to them."