Sammy, a 2.5-year-old boy, arrives at the family clinic for the first time complaining of fever and increasing “wet cough” for 6 days.

Sammy, a 2.5-year-old boy, arrives at the family clinic for the first time complaining of fever and increasing “wet cough” for 6 days. Sammy’s mother revealed that he has been diagnosed with asthma and has an inhaler to use for wheezing or coughing. When Sammy was about 9 months old, he began to experience similar episodes of “wet” cough and fever, which were diagnosed as bronchitis or pneumonia, and he would improve when treated with antibiotics and his inhaler. However, during the past year, these episodes have become more frequent and the coughs occur almost daily now. His sputum was often thick and purulent. He has daily nasal congestion that must be aspirated using saline and a suction bulb in his nares. Sammy does not attend daycare and has no tobacco exposure. His mother believes he is “small for his age.” Sammy’s mother told the clinician that his stools are malodorous, float, and sometimes appear to have drops of oil on them.

The clinician’s physical findings reveal an ill-appearing child whose height and weight are at the third percentile for his age. His temperature is 101°F (38.3°C) and respiratory rate is 32 breaths/minute. He is breathing with his mouth open. Auscultation of lung sounds reveals crackles and rhonchi in the upper part of the lung with some occasional wheezing. His fingers show clubbing. Chest radiograph shows some opacity in the upper lobes with some ring-shaped opacities; the radiologist interpreted the findings as bronchiectasis.

The physician suspects that Sammy may have cystic fibrosis (CF) and requests a sweat chloride test, serum electrolyte panel, and CFTR mutation analysis. The results are shown below:

Tests (units) Results RI/Cutoff/Interpretation
*Not the preferred first-tier molecular test for carrier screening or diagnosis. This test is used to identify mutations in individuals with a clinical diagnosis of CF when CFB/Cystic Fibrosis Mutation Analysis, 106-Mutation Panel is negative or uninformative.
Sweat chloride (mmol/L) 58 >6 months 40–59 (CF possible)
Sodium (meq/L) 128 136–45
Potassium (meq/L) 4.5 3.5–4.5
Chloride (meq/L) 94 98–107
TCO2 (meq/L) 25 23–29
*CFTR gene, full gene analysis (specimen of choice is a lavender-top tube) Positive for the presence of Δ508 mutation
  1. Why are the blood sodium and chloride results abnormal and how does CFTR protein affect these electrolytes?
  2. What is the cause of the malodorous and floating stools?