Sweat testing

The analysis of sweat for increased electrolyte concentration is used to confirm the diagnosis of cystic fibrosis (CF). CF is recognized as a syndrome with a wide spectrum of clinical presentations associated with a defect in the cystic fibrosis transmembrane conductance regulator protein (CFTR), a protein that normally regulates electrolyte transport across epithelial membranes. (For a more detailed discussion of CF, see Chapter 40.) Several hundred mutations of CFTR have been identified. Although mutational analysis is available, it is not informative in all cases, and the sweat test remains the standard for diagnostic testing.  

The United States Cystic Fibrosis Foundation (CFF) states that the diagnosis of CF is based on the following criteria  

Plus laboratory evidence of a CFTR abnormality as documented by elevated sweat chloride concentrations or identification of two CF mutations or m vivo demonstration of characteristic abnormalities in ion transport across the nasal epithelium 

Prom LeGrys VL, Burnett RW, Current status of sweat testing in North America. Arch Pathol Lab Med 1994 118 865-7. Copyright 1994, American Medical Association, 

The sweat test occurs in three phases sweat stimulation by pilocarpine iontophoresis collection of the sweat onto gauze, filter paper, coil, patch, or capillary tube and qualitative or quantitative analysis of sweat chloride, sodium, conductivity, or osmolality. A survey of 753 laboratories (Table 27-3) performing sweat testing revealed that 47% analyze chloride, 46% analyze conductivity, and less than 7% analyze sodium or osmolality.  

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Diagnosis of CF is based on two separate elevated sweat chloride concentrations of greater than or equal to 60 mEq/L (or mmol/L) obtained through pilocarpine iontophoresis (referred to as the sweat test ). Genetic testing (CFTR mutation analysis) may be performed to confirm the diagnosis, screen in utero, or detect carrier status. More than 70% of diagnoses are made by 12 months of age and almost all are made by age 12. 

T. Bray, G. C. F. Clark, G. J. Moody and J. D. R. Thomas, A Perspective of Sodium and Chloride Ion-Selective Electrode Sweat Tests for Screening in Cystic Fibrosis, University of Wales, Cardiff (1975). 

Exsudation par 6tuvage. A French test described in Vol 1 of Encycl, p XI, under Exudation (or Sweating) Tests... 

Fr for Resistance to Exudation Test). One of the Fr methods is described in Vol 1, of Encycl, under "Exudation (or Sweating)Test, p XI Another test is in Daniei,Dict(1902), pp 293, under Exsudation and the 3rd test in. Pepin Lehalleur (1935), 61... 

Extent of Propagation of Explosion. See Ability to Propagate Detonation in this section Exudation(or Sweating) Tests(Exsudation Esaais, in Fr) (Ausschwitzungoproben, in Ger). The purpose of the exudation test is to determine whether expls, such as dynamites, DKT, TNT, etc would release any li j in storage, especially in hot climates... 

British Tests. See Physical Tests for Determining Explosive and Other Properties Vol 1 and specifically the following British tests a)Ballistic Pendulum Test, p VII b)Exudation(ot sweating) Tests, p XI c)F7 lest(Figure of Insensitiveness Test) p XII Fragment Gun, p XII d)Friction Sensitivity Tests, p XIII e)Hopkinson s Pressure Bar Test, p XVI and i)Silvered Vessel Test or Waltham Abbey Silver Vessel Test, p XXIV... 

Carter, E.P., et al. 1984. Improved sweat test method for the diagnosis of cystic-fibrosis. Arch Dis Child 59 919. 

Parad, R. B., et al. (2005), Sweat testing infants detected by cystic fibrosis newborn screening, J. Pediatr., 147(3, Suppl), S69-72. 

Q2 How is the sweat test for diagnosis of cystic fibrosis performed ... 

Q2 In the sweat test, sweating is induced by passing a weak electric current across an area of skin treated with the secretory stimulant pilocarpine. The current enhances the ability of pilocarpine to penetrate skin and so local secretion of sweat is induced. When this test was performed on Carmen, the diagnosis was confirmed her sweat was found to contain 100 mmol l-1 chloride, normally this is expected to be <60 mmoll-1. 

Pilocarpine 208 Cation Sweat test (cystic fibrosis) 166... 

Sweat testing is one of the few clinical chemistry tests involving direct patient contact. Patients often have questions about the sweat test that their physicians may not have answered. Patient educational materials on sweat testing have been produced by the CFF in EngHsh and Spanish and include both written and video material. 

Testing procedures should minimize the opportunity for evaporation and contamination of the sweat sample. Detailed instructions on minimizing evaporation and contammation can be found in the NCCLS sweat testing document. ... 

Specimen Weight and Collection Time To have a valid sweat testing result, determination of and adherence to a minimum sweat weight or volume are critical. The requirement for a minimum amount is physiological, to ensure an appropriate sweat rate and sweat electrolyte concentration. It is independent of the instrumentation used to measure sweat electrolytes. Unfortunately, this is poorly understood, leading to false-positive and false-negative sweat test results, which have a significant implication for patient care. Sweat electrolyte concentration is related to sweat rate. 

Unreliable methodology, technical errors, and errors in interpretation can all lead to erroneous sweat test results. Methods that do not quantitate sweat collected or do not have an established minimum sample volume or weight are subject to false-negative results because an adequate sweat rate cannot be ensured. 

Physicians should be aware of the clinical spectrum of CF and appropriately order a sweat test on patients suspected... 

The results of the sweat test must be interpreted in light of the patient s clinical presentation by a physician knowledgeable about CF. There are several conditions other than CF that are associated with elevations in sweat electrolytes (Box 27-1). These conditions usually are distinguishable from CF based on the patient s clinical presentation. 

From National Committee for Clinical Laboratory Standards Sweat Testing Sample Collection and Quantitative Analysis Approved Guideline. NCCLS Document C34-A2. Viilaiiova, PA, National Committee for Clinical Laboratory Standards, 2000, p. 30,... 

Brand PLP, Gerritsen J, van Aalderen WM. A baby with eczema and an abnormal sweat test. Lancet 1996 348 932. 

Cystic Fibrosis Foundation Center Committee Sweat Testing Guidelines. Bethesda, MD Cystic Fibrosis Foundation (http //www.cff.org), 2005. 

Denning CR> Huang NN, Cuasay LR, et al. Cooperative study comparing three methods of performing sweat tests to diagnose cystic fibrosis. Pediatrics 1980 66 752-7. 

LeGrys VA. Sweat testing for the diagnosis of cystic fibrosis Practical considerations. J Pediatr 1996 129 892-7. 

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