Collection Instructions

Specimen Collection:

Samples are collected using Macroduct Advanced® microcups by Cystic Fibrosis Center staff in accordance with the guidelines of the Cystic Fibrosis Foundation and CLSI Document C34-A4. The Cystic Fibrosis Center is solely responsible for the collection of all sweat specimens at the University of Chicago, and provides all trained staff and equipment necessary to perform these procedures.

Sweat is collected by the care center using Wescor pilocarpine iontophoresis.

To increase the likelihood of collecting an adequate sweat specimen, sweat chloride testing can be evaluated in asymptomatic newborns with a positive newborn screen result or positive prenatal genetic test when the infant is at least ten days old, greater than 36 weeks gestation, and weighs >2kg. Sweat chloride testing should be performed as soon as possible at or after 10 days of life, ideally by four weeks of age. Sweat collections acquired in newborns >3.5kg (versus >2kg) improve specimen acceptability rates by 25% and should be considered when assessing the risk of a quality not sufficient (QNS) collection versus the need to obtain diagnostic information.

In symptomatic newborns (eg, those with meconium ileus), sweat chloride can be evaluated as early as 48 hours after birth if an adequate sweat volume can be collected; although, the likelihood of an inconclusive result may be greater at this age.

The average sweat rate should exceed 1 g/m²/min, which in general corresponds to a minimum sample weight of about 75 mg of sweat collected on a 2 x 2 inch (5.1 x 5.1 cm) gauze or filter paper and about 15 µL of sweat collected in Macroduct coil in 30 minutes. Volume verification should be performed for any specimen that might be near the 15 µL threshold. Samples less than the required volume or weight must not be analyzed.

Sweat must not be stimulated or collected from the head or trunk. Sweat must not be stimulated or collected from an area of diffuse inflammation, such as a rash or eczematous lesion, because of the likelihood of contamination by serous fluid.

The sweat collection time may not exceed 30 minutes.

The electrodes used for stimulation must be placed so that current does not cross the trunk, to avoid the possibility of current crossing the heart, resulting in cardiac depolarization.  The iontophoretic current source must be battery-powered, to avoid the possibility of patient exposure to line voltage. The area of stimulation must be equivalent to the area of sweat collection. For manually controlled devices, iontophoresis must be performed for no more than five minutes at a current less than 4 mA, to prevent burns. The iontophoresis unit must be tested by qualified personnel (such as engineering personnel) for current leakage and current control at defined frequencies and records retained.

Iontophoresis must be withheld from patients receiving oxygen by an open delivery system. While the possibility of an explosion due to the generation of an electrical spark is remote, it cannot be ignored. Often, these patients can temporarily receive oxygen via a facemask or nasal cannula, in which case sweat testing can be done.

Sweat must not be collected over areas of urticaria (hives) or burns.  In some rare instances a patient may develop an area of urticarial or small localized burns.  If this is observed the collection procedure must be discontinued immediately and appropriate medical attention obtained.  Documentation of follow-up treatment is maintained by the Cystic Fibrosis Center in the Department of Pediatrics. 

Collection Steps:

1. Wash the patient's skin thoroughly with distilled, deionized water. Leave the skin slightly wet after washing the area where the electrode will be attached or add a drop of distilled or deionized water to either the skin or the Pilogel surface (after installation in the electrode). Repeat after stimulation and before collection
2. Avoid touching the collecting surface of the coil
3. Fasten the collector to the extremity with firm strap pressure. Test for proper attachment after sweat appears in the coils
4. Do not attempt to remove the entire collector assembly from the patient's extremity before separating the coil from the main body. Loss of specimen may occur
5. Do not contaminate the nippers or sweat dispensing needle with sweat sample

Collection Device:

The sweat collection device must be designed for use with the appropriate iontophoresis system so that the stimulation and collection area are equivalent and the appropriate minimum acceptable sweat volume or weight can be achieved. Examples of acceptable combinations include:

• Stimulation with Pilogel iontophoresis and collection into Macroduct coils
• Stimulation with copper electrodes over gauze/filter paper pilocarpine pads and collection into gauze/filter paper
• Stimulation and collection into Nanoduct conductivity cell

Examples of unacceptable combinations include:

• Stimulation with Pilogel iontophoresis and collection into gauze/filter paper
• Stimulation with Polychrome iontophoresis and collection into Macroduct coils, gauze or filter paper
• Stimulation with copper electrodes over gauze/filter paper pilocarpine pads and collection into Macroduct coils