Diagnostic Highlights

General Comments: Prenatal and genetic tests are performed to identify fetal disease and carrier status. Failure to thrive and frequent upper respiratory infections often lead to diagnostic testing to confirm the CF diagnosis.

Test

Normal Result

Abnormality with Condition

Explanation

Quantitative sweat electrolyte test (pilocarpine iontophoresis) Genotyping

No mutations

>60 mEq/L (40-60 mEq/L is highly suggestive) >90 mEq/L (70-90 mEq/L is highly suggestive)

Probes identify the most common 87 of the 900 known mutations; finding of 2 CFTR mutations along with clinical symptoms is diagnostic for the condition. Negative results on genotype analysis do not exclude the diagnosis of CF.

Almost all patients with CF have increased chloride and sodium in their sweat

Genotyping identifies genetic alterations

Other Tests: Serum electrolytes, chest x-ray, arterial blood gases, pulmonary function tests, semen analysis, nasal potential difference measurement of the nasal mucosa, pulmonary function tests, bronchoalveolar lavage, and sputum microbiology.

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