A rapid and sensitive automated light scattering immunoassay for serum C-reactive protein and the definition of a reference range in healthy blood donors

Development of nanobody-based flow injection chemiluminescence immunoassay for sensitive detection of human prealbumin

Nanobodies, derived from camelid heavy-chain antibodies, have novel and impactful applications in clinical diagnostics. Our objective is to develop a nanobody-based chemiluminescence immunoassay for sensitive detection of human prealbumin (PA). In this context, a phage display nanobody library is constructed via immunizing dromedary camel with human prealbumin. Three nanobodies have been identified by five successive bio-panning steps. Based on their high expression level and good affinity, two out of three are chosen for further study. Magnetic beads (MBs) were functionalized with PEI by acylamide bond formed between the carboxyl group on the surface of the MB. Then, an anti-PA nanobody (Nb1) can be effectively immobilized onto the surface of the functionalized MB using glutaradehyde as the link. The modified MBs with Nb1 can specifically capture the target PA and reacted with silica nanoparticles with co-immobilized HRP and anti-PA nanobody (Nb2). The concentration of PA was detected by flow injection chemiluminescence. When using MB/PEI as the carrier of anti-PA Nb1, the CL signal significantly increased to 4-fold compared with the signal using MB without PEI modification. The CL signal was further amplified to 5-fold when Si/Nb2 was used as the signal probe. Under optimized conditions, the present immunoassay exhibited a wide quantitative range from 0.05 to 1000 μg L(-1) with a detection limit of 0.01 μg L(-1). The sensitivity of the proposed immunoassay offers great promises in providing a sensitive, specific, time saving, and potential method for detecting PA in clinical settings.

Fluorescent nanoparticles as labels for immunometric assay of C-reactive protein using two-photon excitation assay technology

We describe the use of fluorophore-doped nanoparticles as reporters in a recently developed ArcDia TPX bioaffinity assay technique. The ArcDia TPX technique is based on the use of polymer microspheres as solid-phase reaction carrier, fluorescent bioaffinity reagents, and detection of two-photon excited fluorescence. This new assay technique enables multiplexed, separation-free bioaffinity assays from microvolumes with high sensitivity. As a model analyte we chose C-reactive protein (CRP). The assay of CRP was optimized for assessment of CRP baseline levels using a nanoparticulate fluorescent reporter, 75 nm in diameter, and the assay performance was compared to that of CRP assay based on a molecular reporter of the same fluorophore core. The results show that using fluorescent nanoparticles as the reporter provides two orders of magnitude better sensitivity (87 fM) than using the molecular label, while no difference between precision profiles of the different assay types was found. The new assay method was applied for assessment of baseline levels of CRP in sera of apparently healthy individuals.

Occult pretransplantation systemic inflammation and posttransplantation vascular changes in a primate arterial allograft model

BACKGROUND

Occult systemic inflammation, as manifested by increased levels of C-reactive protein (CRP), identify patients at increased risk for renal allograft rejection. The mechanisms linking occult systemic inflammation to these adverse outcomes remain unclear. The purpose of this study was to examine the anatomic and physiologic effects of occult pretransplantation systemic inflammation on posttransplantation allograft outcome in a nonhuman primate model.

METHODS

Seventy-one healthy male Rhesus macaques were stratified into quartiles based on serum CRP. Five high quartile and six low quartile animals underwent common iliac artery transplantation from male donors. Duplex ultrasound measured graft flow at 3 weeks postoperatively; luminal narrowing was assessed by graft/femoral peak systolic velocity ratio. At 6 weeks, the grafts were harvested and morphometry studies were performed. Vessel wall changes were assessed by measuring the intimal medial area.

RESULTS

The allografts placed in high CRP quartile animals had more luminal narrowing by 3 weeks than those placed in low quartile animals, as evidenced by a higher mean graft/femoral peak systolic velocity ratio (1.6 vs. 0.90, P=0.006). Morphometry studies after graft harvest showed increased vessel wall area in the high quartile group versus the low quartile group (1.39 mm vs. 1.03 mm, P=0.018).

CONCLUSIONS

Occult pretransplantation systemic inflammation is associated with increased intimal thickening and stenosis after arterial allograft transplantation in a primate model. Additional studies are needed to confirm these results and to further investigate potential mechanisms linking pretransplantation systemic inflammation to adverse outcomes after transplantation.

Persistent elevation of C-reactive protein and ischemic heart disease in patients with continuous ambulatory peritoneal dialysis

We evaluated the association between a persistent elevation of C-reactive protein (CRP) level and the presence or severity of ischemic heart disease (IHD) in patients with continuous ambulatory peritoneal dialysis (CAPD). Seventy-three patients, who were over 40 years old, underwent dipyridamole thallium single photon emission computed tomography (SPECT), and followed-up for more than 1 year were enrolled. We measured stored plasma for CRP every 3 months. Elevation of CRP was defined as greater than or equal to 5 mg/L and persistent elevation of CRP as elevated CRP levels that lasted longer than 6 months. Serum albumin, cholesterol, lipoprotein(a), and plasma fibrinogen were measured at 3 months after the start of CAPD. Twenty-six patients showed an elevation of CRP for more than 6 months during the follow-up period. Twenty-eight patients showed positive findings on thallium SPECT. Coronary angiography showed significant stenosis (narrowing of the diameter more than 50%) in 23 of the 25 patients studied. Seventeen (65%) of 26 patients who had an elevated CRP level for longer than 6 months had positive thallium SPECT. The presence of diabetes, albumin, fibrinogen, and the presence of a persistent elevation of CRP were different between the patients with positive (n = 28) or negative thallium SPECT (n = 45). A multivariate logistic regression analysis showed that a persistent elevation of CRP is the only predictor of positive thallium SPECT (P = 0.002). There was a tendency of association, although it was not statistically significant, between the persistence of CRP elevation and the severity of IHD (P = 0.066). Three of 9 patients who had a persistent elevation of CRP and a negative thallium SPECT had a history of cerebral infarction or peripheral vascular disease. Therefore, 77% (20/26) of an elevated CRP level that lasted longer than 6 months can be explained by the presence of IHD or other atherosclerotic vascular disease. In conclusion, a persistent elevation of CRP level in patients with CAPD was strongly associated with IHD. For patients who have a persistent elevation of CRP without an apparent cause, we recommend a workup for IHD or other atherosclerotic cardiovascular disease.

High sensitivity C-reactive protein (CRP) reference intervals in the elderly

High sensitivity C-reactive protein is a useful marker in clinical practice; however, reference intervals are not available for all age groups. Therefore, the aim of this study was to determine reference intervals for elderly people. The non-parametric reference limits were calculated for the two genders, subdivided into two age classes (50-64 and 65-91 years). In our selected sample population, we did not observe significant gender differences.

Reference interval for serum C-reactive protein in healthy blood donors using the Dade Behring N Latex CRP mono assay

Measurement of the serum concentration of the acute-phase reactant C-reactive protein (CRP) provides an useful objective marker in clinical practice, both in screening for diseases and in monitoring disease activity and response to therapy. The aim of this study was to evaluate the analytical performance of the assay in the concentration range from 0.2 to 15 mg/L, and to determine a reference interval for serum CRP in healthy blood donors using the Dade Behring N Latex CRP mono assay on the Dade Behring Nephelometer II. The assay is a particle-enhanced nephelometric immunoassay with a measuring range of 0.2-1100 mg/L. The sample volume is 40 microL, and the assay time is 6 min. The coefficients of variation for within-run and between-run imprecision studies were between 2.2 and 5.4% in serum pools with CRP concentrations between 1.29 and 11.98 mg/L. Linearity studies showed excellent correlation between the theoretical and the measured values. No interferences were detected from hemoglobin <1.0 mmol/L, bilirubin <512 micromol/L and Intralipid <20 g/L. Blood samples were collected from 268 healthy blood donors (107 females and 161 males) between 20 and 65 years old. The non-parametric reference intervals for serum CRP was calculated to be <0.2-14.7 mg/L in females and <0.2-9.16 mg/L in males. The Mann-Whitney U-test revealed no gender-related difference for serum CRP (p-value=0.72). A common reference interval for serum CRP for both genders was calculated to be <0.2-10.5 mg/L (median 0.98 mg/L, range <0.2-17.3 mg/L).