R&R in blood testing stands for repeatability and reproducibility, and it refers to the accuracy or inaccuracy with which a blood test method behaves when executed under different situations, according to ASTM International. R&R is a means to assess any test method, not exclusively blood tests.
The basic standard of R&R in blood testing describes how to perform an interlaboratory study for obtaining values of variations between results from different laboratories conducting tests on the same sample, states ASTM. R&R uncovers discrepancies between these test results and, in short, describes the nature of the variation.
These variations may be attributed to systematic differences, bias, the test operators, equipment changes and changing environmental conditions within a lab, according to ASTM. Labs that participate in such evaluations undergo a small number of repeats for each test protocol. If the nature of variations in results between tests is what repeatability and reproducibility describes, then the variation itself is the standard deviation.
Labs that utilize testing materials purchased from ASTM require repeatability and reproducibility statements and values, especially when executing standard test methods. Having ranges of previously accessed deviations and consensuses at hand enables labs to produce and then evaluate measurements for a sample, as claimed by ASTM.