Cystic Fibrosis Diagnosis in Newborns, Children, and Adults

Carlo Castellani, MD; Barry Linnane, MB, BCh, BAO, DCH, MRCPI, MRCPCH, MD; Iwona Pranke, PhD; Federico Cresta, MD; Isabelle Sermet-Gaudelus, MD, PhD; Daniel Peckham, MD


Semin Respir Crit Care Med. 2019;40(6):701-714. 

In This Article

Sweat Test

The sweat test is the gold standard for CF diagnosis.[152] It is performed through three steps: sweat induction by pilocarpine iontophoresis (cholinergic stimulation), sweat collection, and measurement of sweat Cl concentration, expressed in mmol/L Cl. Sweat collection is usually performed by the Macroduct system (Wescor Inc, Logan, UT), usable also in young children.

Sweat testing should be conducted at accredited CF care centers by experienced personnel following standard operating procedures[152] and be peer-reviewed at least annually.[94,138] It is mandatory to perform internal quality controls before each sample, as well as regular external quality assurance at least every 2 months.

The diagnosis relies, at all ages, on specific Cl concentration measures. Sweat conductivity which assess total sweat electrolytes concentrations (expressed in mmol/L NaCl equivalents) is a non-diagnostic screening method. A sweat Cl value greater than 60 mmol/L is consistent with a diagnosis of CF, below 30 mmol/L makes the diagnosis of CF unlikely. Some conditions can be associated with an elevated sweat Cl level (Table 3), and some disease causing mutations are frequently associated with values <30 mmol/L, such as 3849 + 10kbC > T, L206W, R347H, and D1152H.

Patients with sweat Cl values between 30 and 59 mmol/L should undergo repeat sweat chloride testing and further evaluation in a Specialist CF Centre, including detailed clinical assessment, extensive CFTR gene mutation analysis, and ancillary CFTR functional tests.[94,141,147,151]