Quantitative Sweat Chloride Testing Remains the Standard for Diagnostic Testing

Quantitative sweat chloride testing remains the standard for diagnostic testing of cystic fibrosis (CF) because:

A) a total gene deletion of the cystic fibrosis (CF) gene cannot be detected by direct mutational analysis.
B) there are many mutations of the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) protein and direct mutational analysis is not always informative.
C) a gene deletion on the X chromosome results in loss of an intracellular receptor protein,which can only be detected by protein analysis.
D) an amino acid deletion in the CFTR gene resulting in the loss of electrolyte transport across cell membranes can only be detected by sweat testing.