A Urine Test for Detection and Management of Cystic Fibrosis

By LabMedica International staff writers
Posted on 16 Nov 2022

Image: The CFTR protein is a channel protein that controls the flow of H2O and Cl- ions into and out of cells inside the lungs. When the CFTR protein is working correctly, as shown in Panel 1, ions freely flow in and out of the cells. However, when the CFTR protein is malfunctioning as in Panel 2, these ions cannot flow out of the cell due to a blocked channel. This causes cystic fibrosis, characterized by the buildup of thick mucus in the lungs (Photo courtesy of Wikimedia Commons)

A simple urine test was developed that both identifies individuals with cystic fibrosis and determines the effectiveness of the drug treatment being used to control the disease.

Cystic fibrosis (CF) is caused by mutations in the CFTR gene that code for the ion channel called CFTR. One important function of CFTR is to regulate the production of fluid and mucus in the lungs and digestive fluids in the intestine. Loss of CFTR function leads to thick mucus in the lungs and reduced amounts of digestive fluids. The consequence is inflammations and blockages that damage the organs. CFTR is also expressed in the kidneys where it alters electrolyte handling.

Investigators at Aarhus University (Denmark) speculated that since in CF renal base excretion is impaired, challenged urine bicarbonate excretion may be a useful in vivo biomarker of cystic fibrosis transmembrane conductance regulator (CFTR) function. Therefore, they conducted a study to evaluate the association between challenged bicarbonate excretion and clinical characteristics in CF patients at baseline, quantify the changes induced by the CFTR modulator drug elexacaftor/tezacaftor/ivacaftor (Kaftrio) on challenged bicarbonate excretion after six months of treatment, and characterize the variation in challenged bicarbonate excretion among healthy adults.

During the study, quantification of urine bicarbonate excretion after an acute oral sodium bicarbonate challenge before and six months after Kaftrio treatment was carried out on 50 adult patients with CF who began CFTR modulator therapy with Kaftrio between May 2020 and June 2021.

Results revealed that at baseline, challenged urine bicarbonate excretion was associated with several CF disease characteristics. Bicarbonate excretion was higher in patients with residual function mutations. A higher bicarbonate excretion was associated with better lung function, pancreatic sufficiency, and lower relative risk for chronic pseudomonas infections. Elexacaftor/tezacaftor/ivacaftor treatment increased bicarbonate excretion, reaching about 70% of that seen in healthy control participants. In healthy control participants, individual bicarbonate excretion at each visit correlated with the individual mean bicarbonate excretion.

“The goal is for the urine test to be used as a clinical tool to determine both the severity of the genetic dysfunction and the medicine’s restorative effect in individual patients with cystic fibrosis,” said senior author Dr. Jens Leipziger, professor of biomedicine at Aarhus University. “The management of cystic fibrosis has changed with the recent introduction of treatments targeting the disease-causing mechanism. As the new treatments aim to improve the functioning of CFTR, the urine test can provide a measurement of whether a given treatment is effective. We know that the medicine is absorbed, metabolized, and excreted differently from person to person. If, with a simple test, we can monitor the effects of the medicine for the individual patient, then we expect that patients will be able to achieve a better treatment result.”

The cystic fibrosis study was published in the November 1, 2022, online edition of the journal Annals of Internal Medicine.

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Aarhus University