New microfluidic, paper-based device a potential diagnostic device for dry eye
A new microfluidic paper-based analytical device (µPAD) effectively and accurately measures lactoferrin levels in tear fluid of patients with dry eye, according to a new study.
“Compared with the lactoferrin concentration obtained using the standard enzyme-linked immunosorbent assay (ELISA) method, the concentration obtained using the new µPAD was reproducible in patients suffering from various types of immune-mediated dry eye disease,” said researchers.
Both the µPAD and ELISA were used to measure lactoferrin concentrations from four patients with graft-versus-host disease (GVHD)-related dry eye disease, three with simple dry eye disease and two healthy controls. Researchers observed high reproducibility of the results, with a positive and significant correlation between both methods (r, 0.886; p=0.006). [Ocul Surf 2018;doi:10.1016/j.jtos.2018.11.001]
Moreover, there was a significant inverse correlation between lactoferrin concentration and the fluorescein score (r, –0.751; p=0.019). Similar trends were observed for the ocular surface disease index (OSDI; r, –0.634; p=0.056) and Rose Bengal (r, –0.609; p=0.067) scores, but significance was not achieved.
On the other hand, the tear breakup time (TBUT; r, 0.750; p=0.111) and Schirmer (r, 0.552; p=0.221) test values tended to be positively associated with lactoferrin levels.
In a parallel analysis, researchers used ELISA alone to analyse tear fluid samples from a group of 22 patients (nine with GVHD-related dry eye, six with other types of dry eye and 7 controls without the condition). This cohort included samples from the seven dry eye patients in the initial analysis.
Researchers found similar trends in terms of the diagnostic criteria for dry eye. TBUT (r, 0.472; p=0.026) and Schirmer (r, 0.400; p=0.090) test values were positively correlated with lactoferrin, while the OSDI (r, –0.546; p=0.009) and Rose Bengal (r, –0.559; p=0.003) scores remained negatively associated.
In both analyses, visual acuity and age were not related to lactoferrin concentrations.
“In our study, a positive correlation was noted between ELISA and a novel paper-based microfluid method even in immune-mediated dry eye disease patients,” said researchers, noting that this is in agreement with a previous study that compared µPAD with ELISA and reported only a 6-percent margin of error. [Analyst 2014;139:1637-1643]
“Slight discrepancies were noted between the significance of the relationship between lactoferrin concentration and clinical variables in analyses of TBUT, Schirmer test values, and Rose Bengal staining scores. However, the overall tendency was similar between the two methods,” they added, explaining that the small sample size may account for these differences.
The novel µPAD method makes use of terbium as a reagent for the detection of fluorescein emission, such that after a 2-µL sample is placed on the µPAD, the intensity of the fluorescence would increase in proportion to the concentration of lactoferrin in the sample.
One important limitation of this method is its limit of detection, which is between 0.21–0.26 pg/µL. This may pose problems in some patients, especially those with severe GVHD-related dry eye disease, where lactoferrin is present in very low concentrations, according to researchers.
Regardless, “[m]easuring lactoferrin using this newly developed µPAD may become a useful tool for the standardized method because it is cheap without high cost instruments, antibody-free, rapid for quantification and easy to perform,” they added.