Pilot Evaluation of Intestinal Current Measurement in Cystic Fibrosis and CRMS/CFSPID Patients in Poland

Background/Objectives: The term 'cystic fibrosis transmembrane conductance regulator-related metabolic syndrome/cystic fibrosis screen positive, inconclusive diagnosis (CRMS/CFSPID)' refers to patients with positive screening tests but without a final diagnosis of Cystic Fibrosis (CF). Intestinal Current Measurement (ICM) is a novel diagnostic technique that may document the abnormal function of the cystic fibrosis transmembrane conductance regulator. Our study aims to compare the cumulative chloride secretory response in the ICM study in the Polish population of CF patients, CRMS/CFSPID, and in a control group. Methods: Forceps rectal biopsies were taken from 40 patients (CF; n = 17 mean age 9.10 ± 4.18 (0.7-17.20); CRMS/CFSPID: n = 16, mean age 6.66 ± 4.83 (0.6-18.0); healthy controls (HC): n = 7, mean age 23.7 ± 9.5 (7.8-34.6). ICM tests were performed in the Ussing Chamber according to standard protocol version 2.7 of the European Cystic Fibrosis Society Diagnostic Network Working Group. Delta short circuit-current (ΔIsc) was measured after carbachol (ΔIsc_carbachol), 3-isobutyl-1-methylxanthine with forskolin (ΔIsc_{IBMX/forskolin}), and histamine (Δisc_histamine) stimulation. Cumulative secretion was calculated for each study group. Results: We obtained statistically significant differences in cumulative chloride secretory response between CF and CRMS/CFSPID (CF ΔIsc_{carbachol+IBMX/forskolin+histamine} 15.32 ± 15.47 µA/cm² vs. CRMS/CFSPID ΔIsc_{carbachol+IBMX/forskolin+histamine} 86.84 ± 37.84 µA/cm²; p < 0.001), and between CF and healthy controls (CF ΔIsc_{carbachol+IBMX/forskolin+histamine} 15.32 ± 15.47 µA/cm² vs. HC ΔIsc_{carbachol+IBMX/forskolin+histamine} 80.16 ± 48.54 µA/cm²; p = 0.005). No differences in cumulative chloride secretion were observed between the CRMS/CFSPID and HC groups. Conclusions: The conducted study suggests that ICM may offer diagnostic value, especially in cases where sweat test results are equivocal.