Investigation of Cystic Fibrosis

Chest X ray of Cystic Fibrosis
Sweat Test

• For the past forty plus years, sweat testing has been the most effective, and therefore the most popular, test for detecting cystic fibrosis.

How sweat test is performed

• The sweat test is performed by using an electrode filled with pilocarpine
• A current is run through the electrodes delivering the pilocarpine under the skin.
• The electrodes are removed and the arm is left to rest for about a one-half hour with the filter paper.
• The filter paper will soak up any sweat released from the person's skin. Once the one-half hour is up, the filter paper is placed into a flask and rinsed to release the sweat from the filter.
• A digital chloridometer is used to measure the concentration of chloride ions in the fluid. If more than 60 mmol/liter is detected, cystic fibrosis is diagnosed.

note:The sweat test may not work well in newborns because they do not produce enough sweat. In that case, another type of test, such as the immunoreactive trypsinogen test (IRT), may be used. In the IRT test, blood drawn 2 to 3 days after birth is analyzed for a specific protein called trypsinogen. Positive IRT tests must be confirmed by sweat and other tests.
Heel Prick Test

• is a common procedure for taking a blood sample from the heel of newborn infants.
• Infants with cystic fibrosis 1 to 2 weeks of age show increased levels of immunoreactive trypsin in the plasma in the neonatal heel-prick test.
• The test is positive if immunoreactive trypsin is greater than 80 mcg/litre. It is currently the best screening test for cystic fibrosis but cannot be done after the first few weeks of life since the immunoreactive trypsin falls as pancreatic insufficiency develops.

Genetic Testing

• The diagnosis of cystic fibrosis can also be confirmed by genetic testing in a person who exhibits one or more typical symptoms or has a history of cystic fibrosis in a sibling.
• Finding two abnormal cystic fibrosis genes (mutations) confirms the diagnosis. However, because genetic testing can confirm only a small percentage of the more than 1000 different kinds of cystic fibrosis mutations, failure to detect two mutations does not exclude a diagnosis of cystic fibrosis.
• The disease can be diagnosed prenatally by performing genetic testing on the fetus using chorionic villus sampling or amniocentesis

Pulmonary Function Test

• may show that breathing is compromised and are good indicators of how well the lungs are functioning.
• reduced VC(Vital Capacity) suggest reduce of lung volume (restrictive lung disease),which is present in many patient with CF with advanced lung disease in whom lung parenchyma is destroyed due to chronic lung infection.Strictly speaking, restrictive lung disease may only be diagnosed is TLC(total lung capacity) is reduced
  
• reduced FEV1 suggest narrowing of airway (obstructive lung disease) which is invariably present in patient with CF
  

Chest X-ray & CT Scan

• chest x-rays and computed tomography may be helpful to document lung infection and the extent of lung damage.
• reduced VC(vital capacity) suggest reduction of lung volume (restrictive lung disease),which is present in many patient with CF with advanced lung disease in whom lung parenchyma has been destroyed due to chronic lung infection.Strictly speaking, restrictive lung disease may only be diagnosed if TLC(Total Lung Capacity) is reduced.
• reduced FEV1 also suggest narrowing of airway (obstructive lung disease) which is almost invariably present in patient with CF
  

Characteristic of CF in Chest X-Ray

• Atelectasis

  • Discoid, segmental, lobar with RUL predominance

• Mucoid impaction

  • Nodular and fingerlike densities along bronchovascular bundle

• Cylindrical or cystic bronchiectasis

  • Peribronchial cuffing

• Hilar adenopathy

• Pulmonary arterial hypertension and cor pulmonale

• Recurrent pneumonias, particularly Staph, Pseudomonas and P. cepacia

• Clubbing and hypertrophic osteoarthropathy can occur

• Recurrent pneumothorax is common

Contributed by Lawrence Oh

Sources:
http://pediatrics.about.com/cs/conditions/l/bl_cf.htm
http://www.merck.com/mmhe/sec04/ch053/ch053a.html