The purpose of this study is to find out whether the High Frequency Digit Triplet test can be used to screen patients with cystic fibrosis for hearing loss in conditions of health and pulmonary exacerbation. It is also designed to find out the youngest age at which a child can perform the test, the prevalence of hearing loss in a CF population and the prevalence of genetic mutations known to be associated with hearing loss in the same population.

Patients will be identified from the clinic list of four Cystic Fibrosis centres (Nottingham University Hospitals NHS (National Health Service) Trust, adults and children, West Midlands Adult Cystic Fibrosis Centre and Birmingham Children's Hospital).

In the first work stream patients 11 years old and over will answer some hearing screening questions and an ear examination and tympanogram. They will then have the new test (the High Frequency Digit Triplet, HFDT, test), the standard tests (Pure tone audiogram (PTA) including high frequencies, Distortion Product Otoacoustic Emissions) and then repeat the new test to look for order effect. These will be compared to validate the HFDT as a screening tool for hearing loss.

In the second work stream the investigators are looking to see if the test is feasible when a patient is unwell and about to start a course of IV antibiotics. The patients will have the same tests as in work stream 1 (though the high-frequency PTA may be modified if they are too unwell to complete it). They will then have the tests repeated at the next clinic visit (approximately 6-8 weeks later).

In the third work stream children aged 5-10 years will have the same tests. This is to discover the youngest age at which the HFDT test can reliably be performed. To ensure that the CF condition does not itself affect the ability to perform the test the investigators will compare CF children to healthy control children the same age.

The investigators will take blood and saliva samples from CF patients to look for mutations in mitochondrial genes which are known to be associated with aminoglycoside induced hearing loss.

Inclusion criteria

Work stream 1

• A diagnosis of CF, confirmed by genotype or sweat test, with characteristic clinical features.
• Aged 11 years and over.
• Informed consent. For age 11 to 18 years, consent will be sought from both the parent and young person (provided the young person is competent).

Work stream 2

• As above but the participant has a pulmonary exacerbation (as defined by Fuch's criteria) requiring intravenous antibiotics.

Work stream 3

• As for work stream 1, defined above.
• CF patients aged 5-10 years
• Healthy control children aged 5-10 years.
• Informed consent from parent with assent from the child.

Genetic Testing

• Informed consent
• Diagnosis of CF as above

Exclusion criteria

• None. In individuals with a hearing aid, we will perform PTA and HFDT tests without the aid.
• Individuals found to have conductive deafness after randomisation will be fully assessed for this prior to continuing with the study.