Comparison of the Abbott Architect BRAHMS and the Biomérieux Vidas BRAHMS Procalcitonin Assays

Clinical and Analytical Performance Evaluation of an Automated Procalcitonin Assay

BACKGROUND

Procalcitonin (PCT) measurement is useful for guiding antibiotic therapy and risk assessment in lower respiratory infections and/or sepsis. This study evaluated clinical and analytical performance of the Vitros® Immunodiagnostic Products B·R·A·H·M·S PCT assay (Vitros PCT).

METHODS

Precision, limits of blank (LoB), detection (LoD), and quantitation (LoQ) were determined for Vitros PCT, along with method comparison and clinical concordance with the B·R·A·H·M·S PCT™-sensitive KRYPTOR™ assay (KRYPTOR PCT). All-cause 28-day mortality was evaluated according to the change in PCT values (ΔPCT) from day 0 through day 4 in samples from 598 intensive care unit patients with sepsis.

RESULTS

Comparison of Vitros PCT and KRYPTOR PCT results yielded a Deming regression slope of 1.057, intercept of -0.010, and correlation coefficient (r) of 0.994. Precision analysis demonstrated within-laboratory coefficients of variation for Vitros PCT ranging from 3.1% to 6.4%. The LoD and observed LoQ were determined as 0.007 and 0.013 ng/mL, respectively. Overall agreement between assay methods was 98.5%, 98.0%, 97.4%, and 97.8%, at PCT clinical decision cutoffs of 0.100, 0.250, 0.500, and 2.00 ng/mL, respectively, with Cohen's Kappa coefficients (κ) > 0.91. ΔPCT values ≤80% vs >80% were associated with increased 28-day-all-cause mortality (P = 0.006).

CONCLUSIONS

Vitros PCT compares well with KRYPTOR PCT, showing excellent agreement at relevant clinical decision cutoffs that have been used for antibiotic decision-making and assessment of risk for sepsis progression. ΔPCT values determined with Vitros PCT were useful for evaluation of 28-day mortality risk in patients with severe sepsis.

Procalcitonin detection in human plasma specimens using a fast version of proximity extension assay

An exciting trend in clinical diagnostics is the development of easy-to-use, minimally invasive assays for screening and prevention of disease at the point of care. Proximity Extension Assay (PEA), an homogeneous, dual-recognition immunoassay, has proven to be sensitive, specific and convenient for detection or quantitation of one or multiple analytes in human plasma. In this paper, the PEA principle was applied to the detection of procalcitonin (PCT), a widely used biomarker for the identification of bacterial infection. A simple, short PEA protocol, with an assay time suitable for point-of-care diagnostics, is presented here as a proof of concept. Pairs of oligonucleotides and monoclonal antibodies were selected to generate tools specifically adapted to the development of an efficient PEA for PCT detection. The assay time was reduced by more than 13-fold compared to published versions of PEA, without significantly affecting assay performance. It was also demonstrated that T4 DNA polymerase could advantageously be replaced by other polymerases having strong 3'>5' exonuclease activity. The sensitivity of this improved assay was determined to be about 0.1 ng/mL of PCT in plasma specimen. The potential use of such an assay in an integrated system for the low-plex detection of biomarkers in human specimen at the point of care was discussed.

Harmonization status of procalcitonin measurements: what do comparison studies and EQA schemes tell us?

Sepsis represents a global health priority because of its high mortality and morbidity. The key to improving prognosis remains an early diagnosis to initiate appropriate antibiotic treatment. Procalcitonin (PCT) is a recognized biomarker for the early indication of bacterial infections and a valuable tool to guide and individualize antibiotic treatment. To meet the increasing demand for PCT testing, numerous PCT immunoassays have been developed and commercialized, but results have been questioned. Many comparison studies have been carried out to evaluate analytical performance and comparability of results provided by the different commercially available immunoassays for PCT, but results are conflicting. External Quality Assessment Schemes (EQAS) for PCT constitute another way to evaluate results comparability. However, when making this comparison, it must be taken into account that the variety of EQA materials consist of different matrices, the commutability of which has not yet been investigated. The present study gathers results from all published comparison studies and results from 137 EQAS surveys to describe the current state-of-the-art harmonization of PCT results. Comparison studies globally highlight a significant variability of measurement results that nonetheless seem to have a moderate impact on medical decision-making. For their part, EQAS for PCT provides highly discrepant estimates of the interlaboratory CV. Due to differences in commutability of the EQA materials, the results from different peer groups could not be compared. To improve the informative value of the EQA data, the existing limitations such as non-harmonized conditions and suboptimal and/or unknown commutability of the EQA materials have to be overcome. The study highlights the need for commutable reference materials that could be used to properly evaluate result comparability and possibly standardize calibration, if necessary. Such an initiative would further improve the safe use of PCT in clinical routine.

Diagnosing serious infections in older adults presenting to ambulatory care: a systematic review

OBJECTIVES

to summarise all available evidence on the accuracy of clinical features and blood tests for diagnosing serious infections in older patients presenting to ambulatory care.

METHODS

systematic review, searching seven databases using a comprehensive search strategy. We included cross-sectional prospective diagnostic studies on (1) clinical features, (2) diagnostic prediction rules based on clinical features alone, (3) blood tests and (4) diagnostic prediction rules combining clinical features and blood tests. Study participants had to be community-dwelling adults aged ≥65 years, in whom a physician suspected an infection. We used QUADAS-2 to assess risk of bias. We calculated measures of diagnostic accuracy and present descriptive statistics.

RESULTS

out of 13,757 unique articles, only six studies with a moderate to high risk of bias were included. There was substantial clinical heterogeneity across these studies. Clinical features had LR- ≥0.61 and LR+ ≤4.94. Twelve prediction rules using clinical features had LR- ≥0.30 and LR+ ≤2.78. There was evidence on four blood tests of which procalcitonin was the most often investigated: levels <0.37 ng/ml (LR- = 0.20; 95%CI 0.10-0.42) were suitable to rule out sepsis in moderately high prevalence situations. Two diagnostic prediction rules combining clinical features and procalcitonin had LR- of ≤0.12 (95%CI 0.05-0.33) and LR+ of maximum 1.39 (95%CI 1.30-1.49).

CONCLUSIONS

we found few studies on the diagnostic accuracy of clinical features and blood tests to detect serious infections in older people presenting to ambulatory care. The risk of bias was mostly moderate to high, leading to substantial uncertainty.

Development of magnetic particle-based chemiluminescence immunoassay for measurement of human procalcitonin in serum

BACKGROUND

Serum procalcitonin (PCT) has been recognized as a primary biomarker in bacterial infections, and monitoring its concentration could help to evaluate the prognosis of sepsis and guide the antibiotic administration. We aimed to establish a fast and accurate immunoassay for PCT quantitation.

METHODS

Our newly developed monoclonal antibodies (mAbs) against human PCT were preliminarily evaluated by enzyme-linked immunosorbent assay and then used to develop a chemiluminescence enzyme immunoassay (CLEIA). The proposed CLEIA was assessed in analytical performance and applied to measurement of serum PCT.

RESULTS

mAb 2D3 and mAb 8F6 were selected as capture and detection antibody respectively, due to the highest sensitivity for PCT detection with no cross reaction to calcitonin gene-related peptides. The proposed CLEIA based on mAb pair of 2D3/8F6-AP was characterized for a working range from 0.03 to 100 μg/L. An excellent correlation was observed between our proposed assay and the VIDAS BRAHMS PCT assay (r: 0.9825).

CONCLUSION

Our newly developed mAbs and CLEIA can serve as important diagnostic tools for measurement of human PCT in serum.

Method Verification Shows a Negative Bias between 2 Procalcitonin Methods at Medical Decision Concentrations

BACKGROUND

Procalcitonin (PCT) concentration increases as a result of systemic inflammation owing to bacterial infection. Many PCT algorithms and medical decision concentrations (MDCs) have been clinically validated using the B·R·A·H·M·S PCT™ sensitive Kryptor™ assay. Alternative PCT assays have recently been approved by the Food and Drug Administration for clinical use in the US and require method verification before clinical implementation.

METHODS

Precision, sensitivity, linearity, reportable range, and reference intervals were verified for the Architect B·R·A·H·M·S PCT assay. Accuracy of the Architect B·R·A·H·M·S PCT assay was evaluated by comparison with the B·R·A·H·M·S PCT sensitive Kryptor assay.

RESULTS

The Architect B·R·A·H·M·S PCT assay was found to be precise (CV, ≤4.6%), sensitive (limit of blank, 0.001 ng/mL; limit of quantitation, ≤0.01 ng/mL), and linear according to the manufacturer's claims. The analytical measurement range (0.20-100.00 ng/mL) and the reference interval (≤0.07 ng/mL) were also verified. Patient result comparisons indicated high agreement at 0.10 ng/mL and 0.25 ng/mL and reduced positive agreement at 0.50 ng/mL and 2.00 ng/mL MDCs owing to negative bias compared with the B·R·A·H·M·S PCT sensitive Kryptor assay.

CONCLUSIONS

The Architect B·R·A·H·M·S PCT assay meets most performance specifications claimed by the manufacturer; however, negative bias at 0.50 ng/mL and 2.00 ng/mL PCT concentrations is evident.