False Positive Diagnosis of Lysosomal Storage Disease Based on Dried Blood Spot Sample; Leucocyte Number of a Challenging Factor

Özet

Aim: Recently dried blood spot (DBS) samples have been recommended as a screening test for Lysosomal Storage diseases. Although DBS samples have many advantagesincluding non-invasiveness, cost and transportation, usage of these samples is limited by its high false positive rate. We aimed to investigate any possible effect of theleucocyte number on enzyme activity in dried blood samples in a retrospective study.Materials and Methods: Data was collected from subjects (n=263) for whom hematological parameters were available in the database of Ege University Hospital. Thelysosomal enzyme activity results (alpha glycosidase, glycocerebrosidase, alpha galactosidase, sphingomyelinase and galactocerebrosidase) were re-evaluated with regard tothe leucocyte number. Enzyme activities were measured using fluorometric and liquid chromatography-tandem mass spectrometry methods.Results: All enzyme activities closely correlated with the total number of leucocyte, since leucocytes are the main source of lysosomal enzymes. Glycocerebrosidase andgalactocerebrosidase presented a positive correlation with the number of neutrophils and sphingomyelinase showed a positive correlation with the number of lymphocytes.When we recalculated the lysosomal enzyme activities with regard to the leucocyte number, the false positive rates for glycocerebrosidase, sphingomyelinase and alphagalactosidase decreased from 20%, 10.5% and 10.8% to 4.5%, 4.4% and 4.2%, respectively.Conclusions: Our data indicated that the enzyme activity in dried blood samples including low leucocyte number might be found lower than reference intervals resulting infalse positive diagnosis. We concluded that the calculation of enzyme activity with regard to the number of leucocytes might produce more reliable results and might be helpfulin decreasing the false positive rate.