Diagnosis: How do you know if you have CF?

AGE OF DIAGNOSIS:  75% of CF patients diagnosed by AGE 2!


NEW NEWBORN SCREENINGS!

in 2001 less than 10% of cases were diagnosed in infancy..

in 2011, 60% of cases were diagnosed in infancy.

WHAT THEY FIND.. DIAGNOSIS MUST HAVE....

●Clinical SYMPTOMS consistent with CF in ONE organ (lungs, pancreas, liver, intestines, skin)

                     

AND

●Evidence of ABNORMAL CFTR:

•Increased sweat chloride on skin ≥60 mmol/L (2 times!)

•2- disease-causing mutations in CFTR from each parent's genes

•Abnormal nasal potential difference

HOW THEY FIND IT....

First...Blood Tests:

A provider will take a small amount of blood generally by poking the heel

What they are looking for...

• CF is associated with increased levels of IRT (immunoreactive trypsinogen) 
• IRT is a protein that is produced by the pancreas

If levels are high there are two options depending on the state you live in:

•  they will repeat the blood test in 2 weeks to rule out other causes of high IRT  
• they will complete a DNA test of the blood looking for mutations in CFTR

Results from DNA test:

• positive if they find 2 mutations in CFTR (one from mom, one from dad)
• negative with only 1 or 0 mutations in CFTR

Next.. SWEAT tests:

A provider will perform a test to make a small part of the baby's skin sweat for collection.  

• Applies an odorless, non-harmful chemical that causes sweat production (called Pilocarpine) over small area on arm or leg 
• covers this area with plastic wrap to promote moisture
• removes the covering and collects the sweat with gauze or filter paper
• sample sent to lab for analysis

Results from sweat tests:

For newborns and infants younger than six months of age:

●

≤29 mmol/L: Normal (CF very unlikely)

●

30 to 59 mmol/L: Intermediate (Possible CF)

●

≥60 mmol/L: Abnormal (Diagnosis of CF)

For infants ≥6 months, children, and adults:

●

≤39 mmol/L: Normal (CF very unlikely)

●

40 to 59 mmol/L: Intermediate (Possible CF)

●

≥60 mmol/L: Abnormal (Diagnosis of CF)

ONE MINUTE CLIP OF SWEAT TEST !

Generally this information can be useful in diagnosis but sometimes a 3rd test may be performed..

Third.. Nasal Potential Difference Test (NFD)

• a non-harmful, non-painful electrode is placed in the nose and a voltage is obtained before and after different chemicals are applied to determine the difference in chloride movement
• determining the movement of chloride is a way to check on the CFTR gene since it codes for this protein channel transporter of chloride

SYMPTOMS of CF in NEWBORNS: (will require testing)

• 20% of CF patients had Meconium Ileus at birth
• however...80-90% of newborns with meconium ileum have CF
• meconium: infant poop, blocks the digestive system
• 45% of CF patients had respiratory symptoms at birth
• 28% of CF patients were diagnosed as Failure to Thrive                                                                           (not meeting growth and development milestones despite proper nutrition)

LATE ONSET OF CF: adults typically present with gastrointestinal symptoms, diabetes mellitus, and infertility


References:
Katkin, J. (2014, June 25). Cystic fibrosis: Clinical manifestations and diagnosis. Retrieved January 30, 2015, from http://www.uptodate.com/contents/cystic-fibrosis-clinical-manifestations-and-diagnosis?source=search_result&search=cystic fibrosis diagnosis&selectedTitle=1~150