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In the clinical laboratory, knowledge of and the correct use of clot activators and anticoagulant additives are critical to preserve and maintain samples in optimal conditions prior to analysis. In 2017, the Latin America Confederation of Clinical Biochemistry (COLABIOCLI) commissioned the Latin American Working Group for Preanalytical Phase (WG-PRE-LATAM) to study preanalytical variability and establish guidelines for preanalytical procedures to be applied by clinical laboratories and health care professionals. The aim of this critical review, on behalf of COLABIOCLI WG-PRE-LATAM, is to provide information to understand the mechanisms of the interactions and reactions that occur between blood and clot activators and anticoagulant additives inside evacuated tubes used for laboratory testing. Clot activators - glass, silica, kaolin, bentonite, and diatomaceous earth - work by surface dependent mechanism whereas extrinsic biomolecules - thrombin, snake venoms, ellagic acid, and thromboplastin - start in vitro coagulation when added to blood. Few manufacturers of evacuated tubes state the type and concentration of clot activators used in their products. With respect to anticoagulant additives, sodium citrate and oxalate complex free calcium and ethylenediaminetetraacetic acid chelates calcium. Heparin potentiates antithrombin and hirudin binds to active thrombin, inactivating the thrombin irreversibly. Blood collection tubes have improved continually over the years, from the glass tubes containing clot activators or anticoagulant additives that were prepared by laboratory personnel to the current standardized evacuated systems that permit more precise blood/additive ratios. Each clot activator and anticoagulant additive demonstrates specific functionality, and both manufacturers of tubes and laboratory professional strive to provide suitable interference-free sample matrices for laboratory testing. Both manufacturers of in vitro diagnostic devices and laboratory professionals need to understand all aspects of venous blood sampling so that they do not underestimate the impact of tube additives on laboratory testing.

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BACKGROUND: Though plain plastic/glass tubes are recommended for CSF collection, many laboratories use the commercially available red topped evacuated tubes for CSF collection for biochemical analysis. These red vacutainers affect the assay of some serum parameters. AIM: We evaluated the effect of using red vacutainer for CSF collection on estimation of proteins. METHODS: CSF samples of 50 patients were collected in plain plastic containers. One milliliter from these were transferred to red vacutainers and mixed gently. Protein by pyrogallol red method was estimated directly from plastic containers and from the sample that was poured to red vacutainers. We further prepared different concentrations of bovine serum albumin in normal saline and estimated the O.D. on a spectrophotometer and protein levels on a clinical chemistry analyzer, similarly before and after transferring 1 ml to red vacutainer. RESULTS: The CSF protein levels were significantly higher (p=<0.0001) when transferred to a red vacutainer (median: 81.5 and range:32-324 mg/dl) than that estimated directly from a plain plastic container (Median: 50.5 and range: 20-300 mg/dl) and affected the interpretations in 50% cases. The protein levels were 25, 50, 50 and 355% higher when BSA prepared at concentrations of 100, 50, 25 and 10mg/dl respectively were transferred to red vacutainers. But for 750, 1500 and 3000 mg/dl of BSA concentrations, the increase in red vacutainer was 1.4, 2 and 0.7% respectively. CONCLUSION: Collection of CSF in red vacutainer significantly affects CSF protein estimations, probably due to the presence of clot activator. This might alter the interpretation of result and thus management of the subject. So the red vacutainer should not be recommended for CSF collection.

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