Development and validation of dried matrix spot sampling for the quantitative determination of amyloid β peptides in cerebrospinal fluid

Pre-cut Filter Paper for Detecting Anti-Japanese Encephalitis Virus IgM from Dried Cerebrospinal Fluid Spots

BACKGROUND

The use of filter paper as a simple, inexpensive tool for storage and transportation of blood, 'Dried Blood Spots' or Guthrie cards, for diagnostic assays is well-established. In contrast, there are a paucity of diagnostic evaluations of dried cerebrospinal fluid (CSF) spots. These have potential applications in low-resource settings, such as Laos, where laboratory facilities for central nervous system (CNS) diagnostics are only available in Vientiane. In Laos, a major cause of CNS infection is Japanese encephalitis virus (JEV). We aimed to develop a dried CSF spot protocol and to evaluate its diagnostic performance using the World Health Organisation recommended anti-JEV IgM antibody capture enzyme-linked immunosorbent assay (JEV MAC-ELISA).

METHODOLOGY AND PRINCIPAL FINDINGS

Sample volumes, spotting techniques and filter paper type were evaluated using a CSF-substitute of anti-JEV IgM positive serum diluted in Phosphate Buffer Solution (PBS) to end-limits of detection by JEV MAC-ELISA. A conventional protocol, involving eluting one paper punch in 200 μl PBS, did not detect the end-dilution, nor did multiple punches utilising diverse spotting techniques. However, pre-cut filter paper enabled saturation with five times the volume of CSF-substitute, sufficiently improving sensitivity to detect the end-dilution. The diagnostic accuracy of this optimised protocol was compared with routine, neat CSF in a pilot, retrospective study of JEV MAC-ELISA on consecutive CSF samples, collected 2009-15, from three Lao hospitals. In comparison to neat CSF, 132 CSF samples stored as dried CSF spots for one month at 25-30 °C showed 81.6% (65.7-92.3 95%CI) positive agreement, 96.8% (91.0-99.3 95%CI) negative agreement, with a kappa coefficient of 0.81 (0.70-0.92 95%CI).

CONCLUSIONS/SIGNIFICANCE

The novel design of pre-cut filter paper saturated with CSF could provide a useful tool for JEV diagnostics in settings with limited laboratory access. It has the potential to improve national JEV surveillance and inform vaccination policies. The saturation of filter paper has potential use in the wider context of pathogen detection, including dried spots for detecting other analytes in CSF, and other body fluids.

Development, validation and clinical application of a novel method for the quantification of efavirenz in dried breast milk spots using LC-MS/MS

OBJECTIVES

This manuscript describes the development, validation and clinical application of a novel method for the quantification of the antiretroviral drug efavirenz in dried breast milk spots using LC-MS.

METHODS

Dried breast milk spots were prepared by spotting 30 μL of human breast milk on each circle of Whatman 903 Protein Saver cards. Chromatographic separation was achieved on a reverse-phase C18 column with 1 mM ammonium acetate in water/acetonitrile using a solvent gradient at a flow rate of 400 μL/min and detection was by TSQ Quantum Access triple quadrupole mass spectrometer equipped with a heated electrospray ionization source. The method was applied to characterize the breast milk pharmacokinetic profile of efavirenz in HIV-positive nursing mothers receiving regimens containing 600 mg of efavirenz once daily.

RESULTS

The assay was validated over the concentration range 50-7500 ng/mL. Accuracy ranged between 95.2% and 102.5% and precision ranged between 1.05% and 9.53%. The average recovery of efavirenz from dried breast milk spots was 106.4% and the matrix effect was 8.14%. Stability of efavirenz in dried breast milk spots and processed samples at room temperature, -40°C and -80°C was demonstrated. In the pharmacokinetic study, the mean (SD) AUC0-24, Cmax and Cmin of efavirenz in breast milk were 59,620 ng·h/mL (17,440), 4527 ng/mL (1767) and 1261 ng/mL (755.9), respectively. The mean (range) milk-to-plasma concentration ratio over the dosing interval was 0.78 (0.57-1.26).

CONCLUSIONS

The dried breast milk spot method is simple, robust, accurate and precise, and can be used in settings with limited resources.