Cystic_Fibrosis_Diagnosis_Flashcards
What is the primary diagnostic test for cystic fibrosis (CF)?
The primary diagnostic test for cystic fibrosis (CF) is the sweat test.
What is the characteristic finding in the sweat test for patients with CF?
Patients with CF have abnormally high sweat chloride levels.
What is the normal value for sweat chloride in the sweat test?
The normal value for sweat chloride in the sweat test is less than 40 mEq/l.
What value of sweat chloride indicates CF?
A sweat chloride value greater than 60 mEq/l indicates CF.
What are some causes of false positive sweat test results?
Causes of false positive sweat test results include malnutrition, adrenal insufficiency, glycogen storage diseases, nephrogenic diabetes insipidus, hypothyroidism, hypoparathyroidism, G6PD, and ectodermal dysplasia.
What is the most common reason for false negative sweat test results?
The most common reason for false negative sweat test results is skin oedema.
What condition often leads to skin oedema causing false negative sweat test results?
Skin oedema causing false negative sweat test results is often due to hypoalbuminaemia/hypoproteinaemia secondary to pancreatic exocrine insufficiency.
SUMMARISE CF DIAGNOSIS
Cystic fibrosis: diagnosis
Sweat test
patient’s with CF have abnormally high sweat chloride
normal value < 40 mEq/l, CF indicated by > 60 mEq/l
Causes of false positive sweat test
malnutrition
adrenal insufficiency
glycogen storage diseases
nephrogenic diabetes insipidus
hypothyroidism, hypoparathyroidism
G6PD
ectodermal dysplasia
The most common reason for false negative tests is skin oedema, often due to hypoalbuminaemia/ hypoproteinaemia secondary to pancreatic exocrine insufficiency.
A 5-day-old baby has her heel prick test done, and it comes back that she has a raised level of immunoreactive trypsinogen (IRT).
What is the most appropriate next test for this baby?
Blood film
Brain imaging
Chest x-ray
Sweat test
Thyroid function tests
Sweat test
Newborns with a positive heel prick for CF, i.e. they have a raised immunoreactive trypsinogen (IRT) result, get a sweat test, which will be high if they have CF
On day 5 of life, newborns have the heel prick test. They are tested for cystic fibrosis (CF), congenital hypothyroidism, sickle cell disease, and a number of other metabolic diseases. For CF, the levels of IRT are tested, and if they are raised that can indicate CF. The baby should then undergo the sweat test, and if this is raised, this confirms a diagnosis of CF.
