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A Rapid and Specific Microplate Assay for the Determination of Intra- and Extracellular Ascorbate in Cultured Cells
Published on: April 11, 2014
An in-vitro study to characterise analytical interference caused by sodium ascorbate with point-of-care measurement
Tim Webber1,2, Aniket Nadkarni1,2,3, Imogen Asser1
1Intensive Care Unit, Royal Adelaide Hospital, Adelaide, Australia.
Objective:
Mega-dose intravenous sodium ascorbate, the base-salt of vitamin C, is under investigation as a therapy in critical illness. At pharmacologic concentrations sodium ascorbate may interfere with point-of-care (POC) biochemical measurements. This study aims to characterise the impact of ascorbate on point-of-care (POC) lactate and glucose assays.
Design:
Prospective investigator initiated in vitro study using human and ovine blood samples.
Setting:
Blood samples from humans were collected within the clinical trials unit of the Royal Adelaide Hospital. Blood samples from sheep were collected within the South Australian Health and Medical Research Institute (SAHMRI) Pre-clinical Imaging and Research Laboratories (PIRL).
Participants:
Nineteen healthy adults and three sheep.
Interventions:
Whole blood was spiked with 30% sodium ascorbate to achieve concentrations of 5, 10, and 20mmol/L.
Main Outcome Measures:
Lactate and glucose levels were compared with baseline across multiple POC devices, blood gas analysers, and a laboratory colorimetric reference assay.
Results:
Increasing ascorbate caused spurious decreases in blood lactate measured by the colorimetric assay and two POC devices (Epoc® and the StatStrip Xpress®). False increases in blood lactate were observed with one POC device (iSTAT 1®) and with two blood gas analysers (RAPIDPoint® 500 and Radiometer ABL90 Flex), although the latter was not clinically significant. The StatProfile® Prime Plus blood gas analyser showed no interference. For glucose, increasing ascorbate caused spurious elevations in glucose with four POC glucometers (FreeStyle Optium Neo, StatStrip Xpress®, HemoCue® Glucose 201, and Epoc®) and a false decrease with the RAPIDPoint® 500. No interference was observed with the StatProfile® Prime Plus, Radiometer ABL90 Flex, or laboratory assay.
Conclusions:
At pharmacologic concentrations, ascorbate can cause both falsely high and low lactate and glucose readings, depending on the device used. These findings help inform the selection of appropriate devices for future clinical trials of mega-dose ascorbate.
