PhD Studentship: Rapid point-of-care test to guide prescribing of antibiotics
The proposed project aligns with the following two Global Challenge Research Themes - (1) Migration and Displacement; and (2) Vaccines and Infection Disease (including AMR) and will be carried out in conjunction with Dr Lindenmeyer’s project exploring the experiences of migrants in the UK on obtaining or using antibiotics. The experiences of recent migrants of the use of antibiotics can be very different both from white British populations and established minority ethnic groups. This is because of the wide availability of antibiotics without prescription outside North America and Europe. The judicious use of antibiotics among migrant patients could be induced if the primary care professionals communicate their prescribing decisions backed up by objective tests. The optimised use of antibiotics is widely accepted as one of the major solutions for addressing antimicrobial resistance (AMR).
We propose to develop a point-of-care (PoC) test to quantify procalcitonin (PCT) in blood. The test will be used by primary care professionals to guide and communicate appropriate prescribing of antibiotics to people with acute respiratory infections (ARIs). A majority of antibiotics are currently prescribed for ARIs, many of which are either viral or non-severe. A growing body of evidence supports that PCT levels increases rapidly in patients with bacterial ARIs and decreases in response to effective clinical management, whilst viral infections have little effect on PCT levels. Hence, the concentration of PCT in blood is a reliable indicator for diagnosis of bacterial ARIs and guide to antibiotic decisions.
The normal concentration of PCT in blood is between 10 pM and 150 pM. The current methods for measuring PCT levels include enzyme linked fluorescent assay (ELFA), time resolved amplified cryptate emission (TRACE) and chemiluminescent immunoassay; all of which uses serum or EDTA/ heparinised plasma (rather than whole blood) samples to avoid interference with the optical detection method. This in turn requires sample collection followed by preparation by skilled medical professionals, and the tests themselves take 25 - 30 minutes.
This PhD project will develop a novel method for quantifying trace concentrations of PCT in whole blood obtained by fingerprick. Because the concentration of PCT is quite low, a method of rapid pre-concentration and sample clean-up is needed to generate a result in a few minutes during a consultation. To achieve this, we will use a combination of microfluidics and electrokinetics. We will use microchannels filled with hydrogels to create a pH-step between 6 and 7. The hydrogel will exclude larger objects such as red and white blood cells and platelets, but allow transport of PCT and other proteins along the microchannel. On application of an electric field of the correct polarity, PCT will migrate towards the pH step and accumulate there because its isoelectric point (6.5) is between the step pH values. Proteins with isoelectric points outside this range will either not migrate or will migrate past the pH step. We have demonstrated a 1000-fold concentration enhancement in 120 seconds using this approach. To detect PCT, anti-PCT antibodies will be immobilised at the pH step. Unbound interfering proteins with isoelectric points between 6 and 7 will be washed away by reversing the polarity of the electric field. Subsequently, the bound PCT will be detected label-free using optical interferometry. It should be noted that this is an entirely general assay method, and can easily be adapted to other analytes.
The proposed PoC system will be reliable and user-friendly, being based around smartphones/tablets with simple USB-controlled electronics to generate the required drive voltages and using the built-in camera to perform detection. This will provide a solution that is affordable by healthcare systems in both high-middle-income countries (HMICs) and low-middle-income countries (LMICs). The availability of such an objective test to guide primary care professionals’ decision making in prescribing antibiotics will reduce their usage to situations where they are necessary.