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Sweat Test

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Also known as: Sweat Electrolytes; Iontophoretic Sweat Test
Formal name: Sweat Chloride

At a Glance

Why Get Tested?

When to Get Tested?

When a person has symptoms that suggest CF; as a follow-up, confirmatory test to help diagnose CF

Sample Required?

A sweat sample collected using a special sweat stimulation procedure

Test Preparation Needed?

None; however, you may be instructed to avoid applying creams or lotions to your skin 24 hours before the test.

The Test Sample

What is being tested?

The sweat test measures the amount of sodium and chloride in sweat. Sodium and chloride are part of the body's electrolyte balance and combine to form the salt found in sweat. They help regulate tissue fluid balance. Normally, chloride travels in and out of the body's cells, helping to maintain electrical neutrality and water balance. This movement occurs through a protein, the cystic fibrosis transmembrane conductance regulator (CFTR), that serves as a channel, letting chloride out of cells and into the surrounding fluid and also reducing sodium absorption. Sodium levels thus usually mirror those of chloride.

Cystic fibrosis (CF) is caused by a mutation in each of the two copies of the CFTR gene (one copy from each parent). With two mutations, the CFTR protein may be dysfunctional or totally absent. Since CFTR levels are usually highest in the epithelial cells lining the internal surfaces of the pancreas, sweat glands, salivary glands, intestine, and reproductive organs, these are the areas most affected by CF. Dysfunctional or absent CFTR causes the cells to be impermeable to chloride conductance and results in increased sodium and chloride concentrations in sweat.

Two methods of sweat analysis are frequently used: sweat chloride concentration and sweat conductivity measurement. Sweat chloride analysis is recommended as the diagnostic test for CF. Sweat conductivity may be used to screen for CF.

How is the sample collected for testing?

A sweat sample is collected using a special sweat stimulation procedure. A tiny amount of a sweat-stimulating liquid is applied to a small patch of skin on the arm or leg. An electrode is then placed over the site and a weak electrical current stimulates the area. This is a painless procedure that may create a tingling or warm sensation. After several minutes, the area is cleaned and sweat is collected for about thirty minutes, either into a plastic coil of tubing or onto a piece of gauze or filter paper. The sweat obtained is then analyzed.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

No special preparation is needed. However, you may be instructed to avoid applying creams or lotions to the skin 24 hours before the test.

The Test

Common Questions

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Article Sources

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.

Sources Used in Current Review

Hadjiliadis, D. (Updated 2011 May 1). Sweat electrolytes test. MedlinePlus Medical Encyclopedia [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003630.htm. Accessed August 2012.

Sharma, G. (2012 May 15). Cystic Fibrosis. Medscape Reference [On-line information]. Available online at http://emedicine.medscape.com/article/1001602-overview through http://emedicine.medscape.com. Accessed August 2012.

Cotton, S. et. al. (2012 February 26). Multiple Positive Sweat Chloride Tests in an Infant Asymptomatic for Cystic Fibrosis. Medscape Today News from Lab Med v43 (2):1-5. [On-line information]. Available online at http://www.medscape.com/viewarticle/758468 through http://www.medscape.com. Accessed September 2012.

Ooi, C. et. al. (2012 July 27). Comparing the American and European Diagnostic Guidelines for Cystic Fibrosis Same Disease, Different Language? Medscape Today News from Thorax. v67 (7):618-624. [On-line information]. Available online at http://www.medscape.com/viewarticle/766511 through http://www.medscape.com. Accessed September 2012.

Boas, S. et. al. (2012 April 27). Results of a Quality Improvement Program for Sweat Testing to Diagnose Cystic Fibrosis. Medscape Today News from Lab Med v43 (4):12-14 [On-line information]. Available online at http://www.medscape.com/viewarticle/762278 through http://www.medscape.com. Accessed September 2012.

Bender, L. et. al. (2011 September 29). Kids in America Newborn Screening for Cystic Fibrosis. Medscape Today News from Lab Med v42 (10):595-601 [On-line information]. Available online at http://www.medscape.com/viewarticle/750133 through http://www.medscape.com. Accessed September 2012.

Pagana, K. D. & Pagana, T. J. (© 2011). Mosby's Diagnostic and Laboratory Test Reference 10th Edition: Mosby, Inc., Saint Louis, MO. Pp 924-925

Timothy S. Uphoff, Ph.D., D(ABMG), MLS(ASCP)CM.  Section Head Molecular Pathology Laboratory, Marshfield Labs, Marshfield Clinic, Marshfield WI.

Sources Used in Previous Reviews

Thomas, Clayton L., Editor (1997).  Taber's Cyclopedic Medical Dictionary. F.A. Davis Company, Philadelphia, PA [18th Edition].

Pagana, Kathleen D. & Pagana, Timothy J. (2001). Mosby's Diagnostic and Laboratory Test Reference 5th Edition: Mosby, Inc., Saint Louis, MO.

NIDDK (July 1997). Cystic Fibrosis Research Directions. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) [NIH Publication No. 97-4200]. Available online at http://www.niddk.nih.gov/health/endo/pubs/cystic/cystic.htm through http://www.niddk.nih.gov.

CFF. Sweat Testing Procedure and Commonly Asked Questions. Cystic Fibrosis Foundation [On-line information]. Available online at http://www.cff.org/publications01.htm through http://www.cff.org.

Tait, J., et. al. (26 March 2001). Cystic Fibrosis. GENEReviews [On-line information]. Available online at http://www.genetests.org/.

Mayo Clinic (2001, February 09). What is Cystic Fibrosis? Mayo Clinic [On-line information]. Available online at http://www.mayoclinic.com/invoke.cfm?objectid=2CEBF76F-D36A-4D15-B937BFF91AB51438 through http://www.mayoclinic.com.

MEDLINEplus (2002, January 2, Updated). Cystic Fibrosis. MEDLINEplus Health Information [On-line Information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/000107.htm.

MEDLINEplus (2002, January 2, Updated). Sweat Electrolytes. MEDLINEplus Health Information [On-line Information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003630.htm.

MEDLINEplus (2002, January 2, Updated). Trypsin and chymotrypsin in stool. MEDLINEplus Health Information [On-line Information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003594.htm.

Mountain States Genetics (1999, September, Revised). Cystic Fibrosis (CF). Newborn Screening Practitioner’s Manual [On-line information]. Available online at http://www.mostgene.org/pract/prac26.htm through http://www.mostgene.org.

National Institutes of Health (1995, November). Facts About Cystic Fibrosis. National Heart, Lung, and Blood Institute NIH Publication No. 95-3650 [On-line information]. Available online at http://www.nhlbi.nih.gov/health/public/lung/other/cf.htm through http://www.nhlbi.nih.gov/health/public/lung/other/cf.htm.

Quest Diagnostics NEWS (2002, Winter). What is the Best Test to Screen for Cystic Fibrosis? [On-line serial]. PDF available for download at http://www.questdiagnostics.com/hcp/files/02winter_newsletter.pdf through http://www.questdiagnostics.com.

MEDLINEplus (2002, January 2, Updated). Neonatal cystic fibrosis screening. MEDLINEplus Health Information [On-line Information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003409.htm.

Drkoop (2001). Cystic fibrosis. Medical Encyclopedia [On-line information]. Available online at http://www.drkoop.com/conditions/ency/article/000107.htm through http://www.drkoop.com.

MEDLINEplus (2002, January 2, Updated). Trypsinogen. MEDLINEplus Health Information [On-line Information]. Available online at http://www.nlm.nih.gov/medlineplus/ency/article/003560.htm.

Biomedical Hypertext (1999 May 20, last update). Exocrine Secretions of the Pancreas. Colorado State University [On-line information]. Available online at http://arbl.cvmbs.colostate.edu/hbooks/pathphys/digestion/pancreas/exocrine.html through http://arbl.cvmbs.colostate.edu.

UPCMD (1998 – 2002). Cystic Fibrosis. University Pathology Consortium, LLC [On-line information]. Available online at http://www.upcmd.com/dot/examples/00218/description.html through http://www.upcmd.com.

Sainato, D., (2002, March). Genetic Testing for CF Going Mainstream? Clinical Laboratory News, Volume 28.

Peter Jacky, PhD, FACMG. Director of Cytogenetics and Molecular Genetics, Airport Way Regional Laboratory, Portland, OR.

(June 2008) American Lung Association. Cystic Fibrosis Factsheet. Available online at http://www.lungusa.org/site/apps/nlnet/content3.aspx?c=dvLUK9O0E&b=2058829&content_id={2C5B0EF6-D044-4306-AF93-416DE1C89DE8}&notoc=1 through http://www.lungusa.org. Accessed January 2009.

Cystic Fibrosis Foundation. Testing for Cystic Fibrosis, The Sweat Test. Available online at http://www.cff.org/AboutCF/Testing/SweatTest/ through http://www.cff.org. Accessed January 2009.

(June 2006) Coffin, C. Nemours Foundation. Sweat Test. Available online at http://kidshealth.org/parent/general/sick/sweat_test.html through http://kidshealth.org. Accessed January 2009.

Pagana K, Pagana T. Mosby's Manual of Diagnostic and Laboratory Tests. 3rd Edition, St. Louis: Mosby Elsevier; 2006. Pp 707-709.

Cleveland Clinic. Cystic Fibrosis. Available online at http://my.clevelandclinic.org/disorders/cystic_fibrosis/hic_cystic_fibrosis.aspx# through http://my.clevelandclinic.org. Accessed January 2009.

Denise I. Quigley, PhD, FACMG. Co-Director Cytogenetics/Molecular Genetics, Airport Way Regional Laboratory, Portland, OR.

Peter Jacky, PhD, FACMG. Director of Cytogenetics and Molecular Genetics, Airport Way Regional Laboratory, Portland, OR.

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