Features of the pre-analytical stage in quantitative determination of TREC/KREC in peripheral blood

Abstract

The use of dried blood spots (DBS) obtained from the heels of infants has many advantages over the collection of whole blood samples. DNA extracted from DBS can be used to detect genetic diseases by PCR, which has contributed to the development of population-based newborn screening worldwide. Since January 2023, the list of identified diseases includes a group of primary immunodeficiencies (PIDs), associated with the absence or decrease in the levels of T and/or B lymphocytes, determined as part of screening by the levels of TREC and KREC molecules in peripheral blood, respectively. Quantitative analysis requires special attention to biological material. The aim is to evaluate the impact of the preanalytical step on the quantitative analysis of TREC/KREC levels in peripheral blood.The material included 5219 DBS obtained from infants on days 3-4 of life, as well as DBS prepared from the whole blood of 100 apparently healthy individuals aged 18 to 29 years. A comparative analysis of the TREC/KREC molecules number in correctly and incorrectly collected DBS from newborns and adults, as well as depending on the volume of applied blood, was carried out by RT-PCR using test systems to assess the levels of TREC and KREC in peripheral blood. DBS quality was assessed visually.In the first months of the project, a significant number of incorrectly taken samples were identified – over a third of all DNA maps received for each corresponding month. As a result of additional training of medical staff, the amount of incorrectly collected material decreased to a level not exceeding 1% of all monthly samples collected. When using DNA extracted from DBS with application errors, the majority of samples (64% for newborns, 78% for adults) failed to obtain a result. In the remaining cases, the results obtained were significantly lower than the normal levels of TREC/KREC determined in the same samples with correct DBS collection (all p < 0.0001, 95% CI). The volume of blood used when correctly applied to Guthrie cards did not affect the results obtained, TREC and KREC levels were comparable; when comparing the medians calculated for each group of samples, no significant differences were identified (p > 0.05).When quantitatively analyzing TREC/KREC levels in peripheral blood, correctly taken material is fundamental importance to obtain reliable indicators, primarily to exclude false-positive results. To minimize errors in the preanalytical stage, additional training of medical personnel is necessary to control and/or correct errors.