Friday, July 21, 2017

nCD64 as a marker of Sepsis

Several times in my blogs, I have talked about how important it is to make a diagnosis at the fastest turn around time possible. In an attempt to miniaturise the testing platform and obtaining faster results, several technologies have been tested. In context with infections, genome detection and sequencing based technologies are increasingly becoming better and more accessible. Another example is pathogen specific molecular marker detection method on which a good lot of R&D is invested. MALDI-TOF is an excellent example.

Fig 1: Hospitalisation rates for sepsis or septicemia.
Sepsis is a serious issue. Any clinical microbiologist who works in association with the hospital knows the seriousness of sepsis. The terms "Sepsis" and "Septicemia" both refer to a bloodstream infection. Though in a strictly technical sense they mean two different things, they have been interchangeably used in literature and was widely accepted as similar. The earlier definition of sepsis was based on the idea that it is a systemic response and was thus assessed using a systemic inflammatory response syndrome (SIRS) criteria. To date, there is no clear definition of what sepsis is though it is generally agreed that it means circulating pathogen in blood. The diagnosis is based on evidence of fever, respiratory rate and abnormal total WBC count followed by bacterial identification from blood culture. There are no global estimates of sepsis prevalence. Available estimates suggest a range of <1% in a population. However,  there is a significant trend observed everywhere as shown in Fig 1.

In most parts of the globe, a prediction of sepsis is made based on markers such as C reactive protein and procalcitonin levels. Many studies have attempted to come up with a marker. Some of the well-researched markers of sepsis include triggering receptor expressed on myeloid cells-1 (TREM-1), azurocidin, CD64, CD11b etc.

Fig 2: Process schematic of the differential expression-based
cell-counting technology. Source
Studying these markers in the laboratory is not the big deal, since instruments such as Flow cytometers and other sophisticated equipments can do it. But they are not ideal for POCT (Point of care testing). In 2015, this problem was addressed by developing a POCT equipment based on microfluidics. The same group has now come up with improvements in design. The microfluidic biochip is capable of enumerating leukocytes and quantify neutrophil CD64 (nCD64) levels from 10 ml of whole blood without any manual processing. The tech uses whole blood (10ml) which is pumped into the biochip along with lysing and quenching buffers, to lyse erythrocytes. Cells are electrically counted and differentiated based on size using microfabricated electrodes. The CD64+ cells get captured based on their CD64 expression level. The difference in the cell counts is used to calculate nCD64 expression level. See Fig 2.

The authors claim that this technology can have profound results since the assay takes about 30 min and has scope for further improvement. That would be something really usefull to clinicians as a bedside tool for identifying sepsis.

References:

Mervyn Singer et al. The Third International ConsensusDefinitions for Sepsis and Septic Shock (Sepsis-3). JAMA. 2016;315(8):801-810. doi:10.1001/jama.2016.0287

Mayr F, Yende S, Angus D. Epidemiology of severe sepsis. Virulence. 2013;5(1):4-11.

Wang X, Li ZY, Zeng L, Zhang AQ, Pan W, Gu W, Jiang JX. Neutrophil CD64 expression as a diagnostic marker for sepsis in adult patients: a meta-analysis. Crit Care. 2015 Jun 10;19:245. doi: 10.1186/s13054-015-0972-z.

Hassan U, Reddy B Jr, Damhorst G, Sonoiki O, Ghonge T, Yang C, Bashir R. A microfluidic biochip for complete blood cell counts at the point-of-care. Technology (Singap World Sci). 2015 Dec;3 (4):201-213. DOI: 10.1142/S2339547815500090

Hassan U et al. A point-of-care microfluidic biochip for quantification of CD64 expression from whole blood for sepsis stratification. Nat Commun. 2017 Jul 3;8:15949. doi: 10.1038/ncomms15949.

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