© 2005 American Thoracic Society
Consideration of Important Preanalytical Conditions for the Assessment of Circulating Matrix Metalloproteinase-9To the Editor:We read with interest the recent article of Tazaki and colleagues (1) describing increased activity of matrix metalloproteinase-9 (MMP-9) in blood of patients with obstructive sleep apnea syndrome (OSAS). The significance of blood collection as an important preanalytical determinant has not been taken into account by the authors since there is evidence that blood sampling markedly determines the concentration of circulating MMP-9. These facts have previously been discussed in analytical journals (2, 3). Studies from our own laboratory demonstrate the importance of a standard procedure for the collection of specimens for MMP measurement in blood. A report of our own results on the effect of different blood sampling tubes on MMP-9 measurement is shown in Figure 1. Briefly, venous blood samples from eight healthy volunteers were simultaneously collected in different devices for preparation of serum samples. The tubes were centrifuged within 30 minutes after venipuncture at 1,600 x g for 15 minutes at room temperature. The MMP-9 concentration was measured in the supernatants using commercially available ELISA kits (Medac Diagnostika, Wedel, Germany). MMP-9 concentrations in serum samples collected in tubes with clot activator were about threefold higher than in pure serum samples and also higher than the concentrations found in plasma samples (Figure 1).
As platelets and leukocytes contain high concentrations of MMP-9, the varying release of MMP-9 from blood cells during the sampling process could cause these differences (3). These important conditions should be considered in the interpretation of increased MMP levels. Tazaki and coworkers did not clearly distinguish between serum or plasma samples and that may lead to misinterpretation of their results. Recently, the use of blood samples collected with sodium citrate was suggested to avoid the detrimental effect of other anticoagulants or serum and to optimize the diagnostic validity of MMPs in peripheral blood (4).
Departments of Pneumology and Urology, Charité-Universitätsmedizin Berlin, Berlin, Germany FOOTNOTES Conflict of Interest Statement: M.J. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript; K.J. does not have a financial relationship with a commercial entity that has an interest in the subject of this manuscript. REFERENCES
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
