The parents of six-year-old girl have made an appeal to find their daughter a vital bone marrow donor.
More than 300 people have tried unsuccessfully to help Caitlin
Caitlin Behan, from Weston Favell, Northamptonshire, suffers from a rare condition called Fanconi anaemia which affects bone marrow, stopping the blood from fighting infections and preventing clotting.
The only cure for the potentially fatal condition is to find a bone marrow match to allow a transplant - a task which has already seen more than 300 people ruled out during tests in Northampton.
Caitlin's family has arranged for more tests to be carried out on potential donors on Wednesday 12 November in the hope of finding a match.
No other cure
Her father Mark Behan, a Northamptonshire Police sergeant, said: "Caitlin desperately needs a bone marrow transplant, ideally within the next six- to-twelve months; nothing else will cure her.
"I hope people will be able to help."
Detective Inspector Neil McMahon, a colleague of Mr Behan's, said the illness was also taking its toll on Caitlin's father, her mother Bernie and her elder sister Martha.
He said despite searching a database of 300,000 bone marrow donors registered with the Anthony Nolan Trust no match had been found.
"Things are quite desperate really," he said. "She desperately needs a bone marrow transplant. It is the only thing that can save her".
He added: "We are all very concerned. Clearly it must be paramount in Mark's and his wife's minds every second of the day.
"They are a very strong, united family. There is huge support from the police and a lot of the people in Northampton as well."
The latest tests - which follow a recent clinic at Northamptonshire Police headquarters where more than 300 people came to be tested - will be at Northampton Saints Rugby Club in St James, Northampton.
The tests will run from 1600 to 2000 GMT.
Volunteers, who need to be aged between 18 and 43, will be asked to fill in a questionnaire and speak to someone from the Anthony Nolan Trust before having a blood test.
Patients who have Fanconi anaemia are also more susceptible to
leukaemia and cancer.