Development of a fluorescent immunochromatographic test strip for rapid detection of CRP in sweat and effect of different storage conditions on sweat CRP

Background Previous studies have found a certain association between C-reactive protein (CRP) in human sweat and inflammation, but there is no research on rapid detection and storage conditions for CRP in sweat both domestically and internationally.

Objective To develop a rapid semi-quantitative test strip for detecting CRP content in sweat using fluorescence immunochromatography technology and explore the changes in CRP in human sweat under different storage conditions.

Methods The sweat CRP test paper was developed by double antibody sandwich method. On May 24, 2021, from 07:00 to 16:00, sweat samples from 54 young men who were hiking for 50 kilometers in the field were collected. The sweat CRP concentration was measured using test strips and the normal reference range was determined. Taking 10 sweat samples with relatively high CRP values, and different storage temperatures and time were set to detect changes in sweat CRP concentration.

Results The standard curve equation for CRP antigen standard and T/C value was Y=(7.5362 + 0.0105)/1 + (X/2186.5735)^-0.7549 -0.0105, and the R² value was 0.9999. The blank limit (LoB) was 1.94ng/mL, and the detection limit (LoD) was 5.94ng/mL. The absolute value of relative deviation was used to verify the accuracy, and the results were all less than 10%. The cross-reactivity of the results with serum amyloid protein A (SAA) and procalcitonin (PCT) was 0.00% and 0.01%, respectively, and the repeatability and precision in the laboratory were ＜10%. The normal reference range of sweat CRP of target population was ≤ 25 ng/mL. When sweat was stored at different temperatures (4℃, 25℃, 37℃) for 1 hour, there was no significant difference in CRP test. After 3 hours, the concentration of CRP decreased significantly at 4℃ and 25℃, while at 37℃, the concentration change was not significant.

Conclusion The fluorescent immunochromatography test strip for rapid semi quantitative detection of human sweat CRP has good accuracy, specificity, repeatability, and laboratory precision, which could be used for rapid detection of human sweat CRP content in the future with further study and lager sample size.