Protein concentration of subcutaneous interstitial fluid in the human leg. A comparison between the wick technique and the blister suction technique

The wick technique and the blister suction technique are the most common methods for sampling of subcutaneous interstitial tissue fluid in man. The blister suction technique has the advantage of being less invasive than the wick technique, but the reliability of this method is still controversial. The aim of this study was to evaluate whether the simpler blister suction technique using large (8 mm) blisters could replace the wick technique in the investigation of patients with postreconstructive leg edema. Fifteen patients with ipsilateral leg edema following infrainguinal bypass surgery for lower limb atherosclerosis were investigated. The two different fluid sampling techniques were applied simultaneously on both legs. The concentration of total protein and albumin as well as colloid osmotic pressure of the subcutaneous interstitial tissue fluid in the leg were measured in all fluid samples. Agreement analysis was applied to compare the two methods, while the correspondence between the methods was estimated with linear regression analysis. The agreement index was found to be positive for all variables from the operated as well as from the contralateral control limb. Furthermore, all values were within the agreement limit. The best agreement between the two methods was found for colloid osmotic pressure on the operated side. According to the equation of linear regression, there was a slight overestimation of the wick values compared to the observed blister values. In conclusion, there was a good methodological agreement between the blister suction technique and the wick technique. The less invasive blister suction technique should be regarded as the method of choice for the investigation of subcutaneous interstitial tissue fluid in patients with postreconstructive leg edema.