Evaluation of sample handling in relation to levels of tissue inhibitor of metalloproteinases-1 measured in blood by immunoassay

Background: The possible effect of preanalytical conditions such as blood sample preparation and handling on TIMP-1 levels in blood needs thorough investigation. Materials and methods: Blood was collected in dry tubes and tubes containing EDTA and kept at 4degreesC or 20degreesC for 1, 4, 8, 24 or 72 hours before processing into serum or EDTA plasma. in addition, serum and EDTA plasma samples were frozen and thawed 1-8 times. TIMP-1 was measured by ELISA. Results: Time to processing for up to 72 hours did not significantly affect TIMP-1 levels in serum. In EDTA plasma, TIMP-1 levels were stable for up to eight hours; however, if samples were kept for 24 hours or longer the TIMP-1 levels increased (p<0.0001). Repeated freezing and thawing had a significant effect on TIMP-1 levels in serum (p=0.04). In plasma, repeated freezing and thawing for up to six times did not influence TIMP-1. However, in plasma samples exposed to seven or eight freeze/thaw cycles TIMP-1 levels decreased, although not significantly (p=0.23). Conclusions: Handling and processing of blood samples is crucial for TIMP-1 measurement by immunoassay. In serum, TIMP-1 levels are unaffected by time to processing. Plasma samples should be processed within eight hours to avoid a TIMP-1 increase. For the measurement of TIMP-1 in archival material, serum should not be used because TIMP-1 levels are significantly affected by repeated freezing and thawing; archival plasma can readily be used provided that samples have not been frozen and thawed more than six times.