Reasons for Rejecting Blood Samples Analyzed

Errors in clinical laboratories have a great impact on safety and care of patients, and need to be carefully analyzed for improvements to be made in the preanalytical phase, which is responsible for about 70% of errors.

Laboratory scientists at the University Hospital (Porto Alegre, Brazil) carried out an analysis of rejected samples and consequent request for new daily collections of blood for conduction of tests in the following analytical departments: biochemical-immunoassay and hematology. The analysis was performed on data collected from June to August 2010.

The rejection criteria in clotted, hemolyzed, icteric and lipemic samples were visually applied by two technologists and the criterion for the clotted sample was only analyzed in samples collected in ethylenediamine tetra-acetic acid (EDTA) or sodium citrate tubes. The rejection criterion for icteric samples was applied in samples with seric bilirubin levels greater than 25 mg/L that could interfere with the measurement of some tests, such as those for albumin, cholesterol, and total protein. Lipemic samples, in turn, were rejected when serum triglycerides levels exceeded 400 mg/dL, as that may inhibit the tests for amylase, uric acid, urea, bilirubin and total protein.

Of the 77,051 blood samples that were collected during the three months period, 441 (0.57%) were rejected by some type of preanalytical error and therefore had to be recollected. A clot was found in 43.8% of disallowed samples and was found to be the major cause of rejection of samples, followed by 24% with insufficient sample volume. The third most frequent cause for rejecting samples were hemolyzed samples, which involved 17.9% of cases. Other reasons for rejection of samples were misidentification, inappropriate tube, lipemic samples, inadequate sample/additive ratio, and insignificant icteric samples.

The authors concluded that in their laboratory, despite the percentage of preanalytical errors being small, the appearance of laboratory errors could be provoke an adverse impact on patient care. For example, when blood constituents such as potassium, magnesium, iron, lactate dehydrogenase, phosphorus, ammonium, and total protein are falsely increased during hemolysis. In this context, the poor quality specimens could influence laboratory results, which would be clinically incorrect and therefore mislead the physician whose intervention might be unsuccessful. The study was published in January 2012 in the journal Clinical Biochemistry.

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University Hospital Porto Alegre