Tacrolimus Measured in Capillary Volumetric Microsamples in Pediatric Patients-A Cross-Validation Study

A Systematic Literature Review on the Use of Dried Biofluid Microsampling in Patients With Kidney Disease

BACKGROUND

Kidney disease is fairly unique due to the lack of symptoms associated with disease activity, and it is therefore dependent on biological monitoring. Dried biofluids, particularly dried capillary blood spots, are an accessible, easy-to-use technology that have seen increased utility in basic science research over the past decade. However, their use is yet to reach the kidney patient population clinically or in large-scale discovery science initiatives. The aim of this study was to systematically evaluate the existing literature surrounding the use of dried biofluids in kidney research.

METHODS

A systematic literature review was conducted using three search engines and a predefined search term strategy. Results were summarised according to the collection method, type of biofluid, application to kidney disease, cost, sample stability and patient acceptability.

RESULTS

In total, 404 studies were identified and 67 were eligible. In total, 34,739 patients were recruited to these studies with a skew towards male participants (> 73%). The majority of samples were blood, which was used either for monitoring anti-rejection immunosuppressive drug concentrations or for kidney function. Dried biofluids offered significant cost savings to the patient and healthcare service. The majority of patients preferred home microsampling when compared to conventional monitoring.

CONCLUSION

There is an unmet need in bringing dried microsampling technology to advance kidney disease despite its advantages. This technology provides an opportunity to upscale patient recruitment and longitudinal sampling, enhance vein preservation and overcome participation bias in research.

Effects of storage temperature and time on metabolite profiles measured in dried blood spots, dried blood microsamplers, and plasma

The practical advantages of capillary whole blood collection over venipuncture plasma collection for human exposome research are well known. However, before epidemiologists, clinicians, and public health researchers employ these microvolume sample collections, a rigorous evaluation of pre-analytical storage conditions is needed to develop protocols that maximize sample stability and reliability over time. Therefore, we performed a controlled experiment of dried whole blood collected on 10 μL Mitra microsamplers (DBM), 5-mm punches of whole blood from a dried blood spot (DBS), and 10 μL of plasma, and evaluated the effects of storage conditions at 4 °C, -20 °C, or -80 °C for up to 6 months on the resulting metabolite profiles measured with untargeted liquid chromatography-high resolution mass spectrometry (LC-HRMS). At -80 °C storage conditions, metabolite profiles from DBS, DBM, and plasma showed similar stability. While DBS and DBM metabolite profiles remained similarly stable at -20 °C storage, plasma profiles showed decreased stability at -20 °C compared to -80 °C storage. At refrigerated temperatures (4 °C), metabolite profiles collected on DBM were more stable than plasma or DBS, particularly for lipid classes. These results inform robust capillary blood sample storage protocols for DBM and DBS at potentially warmer temperatures than -80 °C, which may facilitate blood collections for populations outside of a clinical setting.

Use of volumetric absorptive microsampling and parallel reaction monitoring mass spectrometry for tacrolimus blood trough measurements at home in pediatric heart transplant patients

Background

Measurement of trough levels for calcineurin inhibitors by venipuncture sampling is a mainstay of patient management in solid organ transplant recipients but challenging in pediatric patients. Volumetric Absorptive Microsampling (VAMS) is a patient-friendly, minimally invasive sampling technique to accurately collect blood. An assay for measurement of tacrolimus in blood using VAMS, coupled with parallel reaction monitoring (PRM) mass spectrometry, was validated in pediatric heart transplant patients.

Methods

Tacrolimus was measured by a newly developed high-resolution PRM assay and compared with low-resolution tandem mass spectrometry (MRM). Dried blood samples were collected from pediatric heart transplant patients (n = 35) using VAMS devices and a satisfaction survey was completed by patients/guardians. Tacrolimus concentrations were compared across whole liquid blood, dried blood spots, and capillary blood, and shipping stability determined.

Results

The PRM assay was linear over a range 1-50 ng/mL, similar to MRM but had greater specificity due to reduced background noise. No significant differences in tacrolimus concentrations were observed between VAMS and venous blood. Tacrolimus dried on VAM tips was stable for 14 days and concentrations were unaffected by postal shipping. The variability in two simultaneously collected at-home patient samples was minimal - average concentration difference was 0.12 ± 0.94 ng/mL (p = 0.6) between paired samples.

Conclusion

A high resolution PRM mass spectrometry assay was developed for home-based dried blood collections for therapeutic monitoring of tacrolimus. The advantage of PRM was enhanced specificity and the VAMS devices provided a simple and convenient approach to blood sampling at home in pediatric heart transplant patients.

Optimizing medication adherence with home-monitoring - A feasibility study using capillary microsampling and mHealth in solid organ-transplanted adolescents

BACKGROUND

Reliable methods to detect and reduce medication nonadherence in solid organ-transplanted (SOT) adolescents are warranted. We aimed to evaluate the feasibility of combining a medication-manager application (TusenTac®-app) with home-sampling of tacrolimus (Tac) in young SOT recipients.

METHODS

Kidney and combined SOT recipients between 14 and 25 years were included. During an 8-week intervention period, the participants were instructed to use the transplant-specific, age-adapted TusenTac®-app daily and to perform weekly at-home Tac trough finger-prick microsampling. Microsample Tac concentrations were controlled against timed venous samples twice. Medication implementation and persistence adherence were measured with BAASIS© questionnaires, TusenTac®-registrations, Tac trough concentration coefficient of variation (CV%) and self-reporting by interview. For comparison, venous Tac trough CV% were obtained from the year before and after the short-term intervention.

RESULTS

Twenty-two recipients were included, two withdrawals, leaving 20; median age 17.9 (14.5-24.8) years, 12 females (60%). The participants registered their dosage intake 88% (1502/1703) of the expected times, and 90% (106/118) of the microsamples were obtained correctly. At inclusion, 11 recipients (55%) were nonadherent assessed with BAASIS© questionnaire, four of these (36%) turned adherent during the intervention period. At the end, 70% reported improved timing-adherence at the interview. There was no significant change in TacCV% from the year before to the year after the short-term intervention. Home-sampling was reliable and measured Tac concentrations accurately.

CONCLUSIONS

Home-monitoring, combining Tac finger-prick microsampling and a medication-manager app, is feasible in adolescent SOT recipients with 70% perceived improvement in medication timing-adherence. There were no significant long-term changes in TacCV% confirming the need for continuous use and individualized interventions.

Volumetric microsampling for simultaneous remote immunosuppressant and kidney function monitoring in outpatient kidney transplant recipients

AIMS

Immunosuppressant and kidney function monitoring are crucial for kidney transplant recipient follow-up. Microsamples enable remote sampling and minimise patient burden as compared to conventional venous sampling at the clinic. We developed a liquid chromatography-tandem mass spectrometry assay to quantify tacrolimus, mycophenolic acid (MPA), creatinine and iohexol in dried blood spot (DBS), and volumetric absorptive microsample (VAMS) samples.

METHODS

The assay was successfully validated analytically for all analytes. Clinical validation was conducted by direct comparison of paired DBS, VAMS and venous reference samples from 25 kidney transplant recipients. Patients received iohexol 5-15 minutes before immunosuppressant intake and were sampled 0, 1, 2 and 3 hours thereafter, enabling tacrolimus and MPA area under the concentration-time curve (AUC) and creatinine-based and iohexol-based glomerular filtration rate (GFR) estimation. Method agreement was evaluated using Passing-Bablok regression, Bland-Altman analysis and the percentages of values within 15-30% of the reference (P₁₅ -P₃₀ ) with a P₂₀ acceptance threshold of 80%.

RESULTS

For DBS samples, method agreement was excellent for tacrolimus trough concentrations (n = 25, P₁₅  = 92.0%) and AUCs (n = 25; P₂₀  = 95.8%) and adequate for creatinine-based GFR trend monitoring (n = 25; P₂₀  = 80%). DBS-based MPA AUC assessment showed suboptimal agreement (n = 16; P₂₀  = 68.8%), but was considered acceptable given its P₃₀ of 100%. The assay performed inadequately for DBS-based iohexol GFR determination (n = 24; P₂₀  = 75%). The VAMS technique generally showed inferior performance, but can be considered for certain situations.

CONCLUSION

The assay was successfully validated for tacrolimus, MPA and creatinine quantification in DBS samples, enabling simultaneous remote kidney function trend monitoring and immunosuppressant therapeutic drug monitoring in kidney transplant recipients.