Nasal potential difference measurements in patients with atypical cystic fibrosis

The diagnosis of cystic fibrosis (CF) is based on characteristic clinical a nd laboratory findings. However, a subgroup of patients present with an aty pical phenotype that comprises partial CF phenotype, borderline sn eat test s and one or even no common cystic fibrosis transmembrane conductance regul ator (CFTR) mutations. The aim of this study was to evaluate the role of na sal potential difference (PD) measurements in the diagnosis of CF patients with an atypical presentation and in a population of patients suspected to have CF, Nasal PD was measured in 162 patients from four different groups: patients with classical CF (n = 31), atypical phenotype (n = it), controls (n = 50), and patients with questionable CF (n = 70), The parameter, or combination of nasal PD parameters was calculated in order to best discriminate all CF patients (including atypical CF) from the non-CF group. The patients with atypical CF disease had intermediate values of PD measure ments between the CF and non-CF groups. The best discriminate model that as signed all atypical CF patients as CF used: e((response to chloride-free an d isoproterenol/response to amiloride)) with a cut-off >0.70 to predict a C F diagnosis. When this model was applied to the group of 70 patients,with q uestionable CF, 24 patients had abnormal PD similar to the atypical CF grou p. These patients had higher levels of sweat chloride concentration and inc reased rate of CFTR mutations. Nasal potential difference is useful in diagnosis of patients with atypical cystic fibrosis, Taking into account both the sodium and chloride transpor t elements of the potential difference allows for better differentiation be tween atypical cystic fibrosis and noncystic fibrosis patients. This calcul ation may assist in the diagnostic work-up of patients whose diagnosis is q uestionable.