Limitations of the sweat test [letter].

We are in agreement with Schwarz et al. when they state that 
the sweat test has some limitations in the diagnosis of cystic 
fibrosis (CF) and that the diagnosis is not justified on the 
basis of an abnormal sweat test unless there is other supporting 
evidence of the disease. In our experience a much greater problem 
of sweat test accuracy occurs in hospitals where the test is 
carried out on a very much smaller number of patients and 
where the laboratory has a much lesser degree of experience than 
that of the authors. We have had a significant number of 
patients referred to our regional children's hospital who have had abnormal 
sweat electrolyte measurements elsewhere, but unequivocally normal measurements when repeated by 
a laboratory carrying out a large number of tests. We have 
not needed to go to the extent of serial collections of 
sweat and of giving spironolactone as have the authors. If we 
obtain a test within the 'grey area' on repeated occasions, we 
carefully seek other evidence of the disease, particularly evidence of pancreatic 
disease. - We do not advocate the general use of spironolactone: 
the merit of this drug in our experiments on certain patients 
was merely to support our suspicion of temporary hyperaldosteronism, a condition 
which might have led to erroneous conclusions in the absence of 
K or Cl determinations. 