Why Dried Blood Spots Are an Ideal Tool for CYP1A2 Phenotyping

Volumetric absorptive microsampling at home as an alternative tool for the monitoring of HbA1c in diabetes patients

Background:

Microsampling techniques have several advantages over traditional blood collection. Dried blood spot (DBS) sampling and blood collection with heparinized capillaries are the standard techniques. Volumetric absorptive microsampling (VAMS) is a novel technique that collects a fixed volume of blood by applying an absorbent tip to a blood drop. In the present study we explored the feasibility of HbA

Methods:

Diabetic patients were enrolled in this study during consultation with the endocrinologist. A venous (adults) or capillary (children) sample was taken for immediate HbA

Results:

The median time between sampling at home and analysis was 3 days. Results of HbA

Conclusions:

Utilizing equipment standard available in the clinical laboratory, the use of home-sampled dried VAMS and DBS is not a reliable tool for the monitoring of HbA

Are capillary DBS applicable for therapeutic drug monitoring of common antipsychotics? A proof of concept

AIM

DBS sampling has been proposed as an alternative for venous blood collection in therapeutic drug monitoring (TDM) of antipsychotics. For implementation in routine practice, a comparison between capillary and venous blood concentrations is mandatory.

RESULTS

A DBS method for quantification of antipsychotics was clinically validated. First, whole blood therapeutic ranges were calculated using the blood:serum ratio. Calculation of DBS:blood ratios and Passing-Bablok regression analysis demonstrated that concentrations obtained by DBS analysis were highly comparable to those obtained by conventional whole blood analysis. Clinical interpretation of serum, whole blood and DBS concentrations were highly identical (sensitivity 91.6-97.6%).

CONCLUSION

This is the first clinical study demonstrating the value of DBS sampling in TDM of antipsychotics.

A Novel, Nondestructive, Dried Blood Spot-Based Hematocrit Prediction Method Using Noncontact Diffuse Reflectance Spectroscopy

Dried blood spot (DBS) sampling is recognized as a valuable alternative sampling strategy both in research and in clinical routine. Although many advantages are associated with DBS sampling, its more widespread use is hampered by several issues, of which the hematocrit effect on DBS-based quantitation remains undoubtedly the most widely discussed one. Previously, we developed a method to derive the approximate hematocrit from a nonvolumetrically applied DBS based on its potassium content. Although this method yielded good results and was straightforward to perform, it was also destructive and required sample preparation. Therefore, we now developed a nondestructive method which allows to predict the hematocrit of a DBS based on its hemoglobin content, measured via noncontact diffuse reflectance spectroscopy. The developed method was thoroughly validated. A linear calibration curve was established after log/log transformation. The bias, intraday and interday imprecision of quality controls at three hematocrit levels and at the lower and upper limit of quantitation (0.20 and 0.67, respectively) were less than 11%. In addition, the influence of storage and the volume spotted was evaluated, as well as DBS homogeneity. Application of the method to venous DBSs prepared from whole blood patient samples (n = 233) revealed a good correlation between the actual and the predicted hematocrit. Limits of agreement obtained after Bland and Altman analysis were -0.076 and +0.018. Incurred sample reanalysis demonstrated good method reproducibility. In conclusion, mere scanning of a DBS suffices to derive its approximate hematocrit, one of the most important variables in DBS analysis.

CYP1A2 phenotyping in dried blood spots and microvolumes of whole blood and plasma

Background: Phenotyping, using caffeine as probe substrate, is a proper method to assess CYP1A2 activity. We evaluated the utility of dried blood spots (DBS) for CYP1A2 phenotyping. Results: LC–MS/MS methods were developed and validated for quantitation of caffeine and its metabolite paraxanthine in DBS, whole blood and plasma. All parameters met the pre-established criteria. While recovery, matrix effects and precision were unaffected by hematocrit (Hct), there was a Hct effect on accuracy, although for the evaluated Hct interval (0.36–0.50) it remained within acceptable limits. The phenotyping methods were successfully applied in healthy volunteers. Conclusion: Excellent method performance and highly comparable phenotyping indices in DBS, whole blood and plasma, combined with the benefits of DBS sampling, illustrate the suitability of DBS-based CYP1A2 phenotyping.