How to best use procalcitonin to diagnose infections and manage antibiotic treatment

Objectives

Procalcitonin (PCT) is a host-response biomarker that has shown clinical value for assessing the likelihood of bacterial infections and guiding antibiotic treatment. Identifying situations where PCT can improve clinical care is therefore highly important.

Methods

The aim of this narrative review is to discuss strategies for the usage and integration of PCT into clinical routine, based on the most recent clinical evidence.

Results

Although PCT should not be viewed as a traditional diagnostic marker, it can help differentiate bacterial from non-bacterial infections and inflammation states – particularly in respiratory illness. Several trials have found that PCT-guided antibiotic stewardship reduces antibiotic exposure and associated side-effects among patients with respiratory infection and sepsis. Studies have demonstrated that patient-specific decisions regarding antibiotic usage is highly complex. Factors to consider include: the clinical situation (with a focus on the pretest probability for bacterial infection), the acuity and severity of presentation, as well as PCT test results. Low PCT levels help rule out bacterial infection in patients with both low pretest probability for bacterial infection and low-risk general condition. In high-risk individuals and/or high pretest probability for infection, empiric antibiotic treatment is mandatory. Subsequent monitoring of PCT helps track the resolution of infection and guide decisions regarding early termination of antibiotic treatment.

Conclusions

PCT possesses high potential to improve decision-making regarding antibiotic treatment – when combined with careful patient assessment, evidence-based clinical algorithms, and continuous notification and regular feedback from all antibiotic stewardship stakeholders. Medical Journals such as Clinical Chemistry and Laboratory Medicine (CCLM) have played a critical role in reviewing and dissemination the high-quality evidence about assays for PCT measurement, observational research regarding association with outcomes among different populations, and interventional research proofing its effectiveness for patient care.

Comparison of a novel automated DiaSys procalcitonin immunoassay with four different BRAHMS-partnered immunoassays

Objectives

Procalcitonin (PCT) is an important biomarker of sepsis and respiratory infections. Various automated immunoassays for measuring PCT in patient plasma are available in medical laboratories. However, due to a lack of international reference material for PCT, the assays are not always comparable.

Design and methods

In this study, we compared a new turbidimetric immunoassay from DiaSys, measured on the Abbott Architect c16000 and Alinity c, with four BRAHMS-associated chemiluminescence immunoassays (Abbott Architect i2000SR, Alinity i, Roche Cobas e411 and DiaSorin Liaison XL) using 120 random patient plasma samples from the clinical laboratory routine at the University Medical Center Goettingen.

Results

The DiaSys assay showed clear differences as compared to the BRAHMS-associated assays when measured on Architect c: i.e. 58% positive mean bias vs. Architect i, 67% vs. Cobas and 23% vs. Liaison. As a result, additional 19% our patients would have a suspected bacterial infection, when using PCT values from the DiaSys assay and commonly accepted decision limits. A crosscheck of the DiaSys calibrator on the BRAHMS-associated systems showed a low recovery of the calibrator material (approx. 50%).

Conclusions

Overall, this study shows significant differences between the DiaSys and BRAHMS-associated assays. This could be attributed to a potential DiaSys calibrator problem. This highlights the need for an international reference material for harmonization of the PCT assays.

Biomarkers Predicting Tissue Pharmacokinetics of Antimicrobials in Sepsis: A Review

The pathophysiology of sepsis alters drug pharmacokinetics, resulting in inadequate drug exposure and target-site concentration. Suboptimal exposure leads to treatment failure and the development of antimicrobial resistance. Therefore, we seek to optimize antimicrobial therapy in sepsis by selecting the right drug and the correct dosage. A prerequisite for achieving this goal is characterization and understanding of the mechanisms of pharmacokinetic alterations. However, most infections take place not in blood but in different body compartments. Since tissue pharmacokinetic assessment is not feasible in daily practice, we need to tailor antibiotic treatment according to the specific patient’s pathophysiological processes. The complex pathophysiology of sepsis and the ineffectiveness of current targeted therapies suggest that treatments guided by biomarkers predicting target-site concentration could provide a new therapeutic strategy. Inflammation, endothelial and coagulation activation markers, and blood flow parameters might be indicators of impaired tissue distribution. Moreover, hepatic and renal dysfunction biomarkers can predict not only drug metabolism and clearance but also drug distribution. Identification of the right biomarkers can direct drug dosing and provide timely feedback on its effectiveness. Therefore, this might decrease antibiotic resistance and the mortality of critically ill patients. This article fills the literature gap by characterizing patient biomarkers that might be used to predict unbound plasma-to-tissue drug distribution in critically ill patients. Although all biomarkers must be clinically evaluated with the ultimate goal of combining them in a clinically feasible scoring system, we support the concept that the appropriate biomarkers could be used to direct targeted antibiotic dosing.

Analytical and clinical performance of the Advansure i3 procalcitonin assay

Procalcitonin (PCT) is a clinically useful biomarker for early diagnosis and subsequent management of sepsis. We evaluated the analytical performance of a new automated chemiluminescent immunoanalyzer-based procalcitonin assay, AdvanSure i3 PCT assay (LG Life Sciences, Korea) on an AdvanSure i3 (LG Life Sciences) and compared it to the Elecsys BRAHMS PCT assay (Roche, Switzerland) on a Cobas e801 (Roche). Analytical performance was performed for the precision, linearity, and method comparison with the Elecsys BRAHMS PCT assay by Clinical and Laboratory Standards Institute guidelines. Clinical evaluations were conducted using 87 residual samples from admitted patients with suspected infection. The patients were classified based on Sepsis-3 classification. The AdvanSure i3 PCT assay exhibited a CV <5.5% for between-run precision and <6.5% for within-laboratory precision. The assay was linear up to 80.32 µg/L (r = 0.990). Statistical analysis showed that the two assays yielded a good correlation (r = 0.996), with a weighted kappa value of 0.94. Median plasma PCT level was significantly different between the non-sepsis and sepsis groups (p < .001) and the non-sepsis and septic shock groups (p < .0018). The AdvanSure i3 PCT assay showed good analytical performance and correlation with the Elecsys BRAHMS PCT assay for the sepsis patients. This new assay can be used as a diagnostic early marker of sepsis in clinical laboratories.

Concordance of Three Automated Procalcitonin Immunoassays at Medical Decision Points

Procalcitonin (PCT) is a useful bacterial infection biomarker with the potential for guiding antibiotic therapy. We evaluated the concordance of three automated PCT immunoassays: Kryptor (BRAHMS GmbH, Hennigsdorf, Germany), Atellica IM 1600 (Siemens Healthcare Diagnostics, Munich, Germany), and Cobas e801 (Roche Diagnostics, Mannheim, Germany). In 119 serum samples with a PCT concentration <5.00 μg/L, Kryptor (reference assay) was compared with the other two immunoassays by Spearman’s rank correlation, regression analysis, and concordance at two antibiotic stewardship medical decision points: 0.25 and 0.50 μg/L. The Atellica IM 1600 and Cobas e801 results showed high correlations with those of Kryptor, with correlation coefficient (ρ) values of 0.97 and 0.99, respectively. However, negative biases were observed in both immunoassays (slope/y-intercept: 0.75/–0.00 for Atellica IM 1600; 0.88/–0.01 for Cobas e801). Atellica IM 1600 and Cobas e801 demonstrated excellent concordance with Kryptor at both medical decision points, with linearly weighted κ values of 0.90 and 0.92, respectively, despite discrepancies, which were more prominent at the 0.25 μg/L medical decision point. Based on these biases and discrepancies, the alternate use of different PCT immunoassays in repeat examinations is inadvisable. Standardization is required before comparing the results of different PCT immunoassays.

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.

Evaluation of the necessity and the feasibility of the standardization of procalcitonin measurements: Activities of IFCC WG-PCT with involvement of all stakeholders

Procalcitonin (PCT) is an important biomarker for sepsis diagnosis and management. To date, there is no higher-order reference measurement procedure (RMP) and certified reference material to achieve global standardization of results and results traceability to the SI units. Although efforts have been made to harmonize PCT results, a number of comparison studies and external quality assessment (EQA) schemes show conflicting results regarding results comparability and to date, equivalence of PCT results across the assays remains questionable in absence of studies relying on commutable EQA materials. In this context, the IFCC initiated activities to fill these gaps through the creation of the working group on standardization of PCT assays that gathers experts from National Metrology Institutes, calibration laboratories, clinicians, biologists, EQA providers and assay manufacturers. Among the activities, a higher order RMP and commutable reference materials are under development to build a robust reference measurement system (RMS). A commutability study is being organized to identify EQA materials that are fit for purpose to reliably estimate the current comparability of PCT results. This work will make it possible to evaluate the necessity and the feasibility for establishing and maintaining a new RMS for PCT assays, if deemed necessary.

Two-center comparison of 10 fully-automated commercial procalcitonin (PCT) immunoassays

Background This two-center study was designed to verify comparability of procalcitonin (PCT) values among 10 different commercial immunoassays. Methods A total number of 176 routine lithium-heparin plasma samples were divided in identical aliquots and simultaneously analyzed with 10 different PCT immunoassays, including Kryptor BRAHMS PCT sensitive, Abbott Architect BRAHMS PCT, Beckman Coulter Access PCT (on Access and DXI), BioMérieux Vidas BRAHMS PCT, Diasorin Liaison BRAHMS PCT, Fujirebio Lumipulse G BRAHMS PCT, Roche BRAHMS PCT (on Cobas E801), Diazyme PCT (on Roche Cobas C702) and SNIBE Maglumi PCT. Results Highly significant correlation was always found across multiple comparisons, with correlation coefficients comprised between 0.918 and 0.997 (all p < 0.001). Bland and Altman plots analysis revealed highly variable bias among immunoassays, ranging between ±0.2% and ±38.6%. Diazyme PCT on Roche Cobas C702 and SNIBE Maglumi PCT displayed the larger overestimation, whilst PCT values were underestimated by Cobas BRAHAMS PCT. The agreement was always >80% (all p < 0.001), but varied largely across multiple comparisons, ranging between 90%-99% at 0.1 μg/L, 81%-99% at 0.25 μg/L, 83%-100% at 0.5 μg/L, 94%-100% at 2.0 μg/L and 90%-99% at 10 μg/L, respectively. The larger disagreement was observed comparing Diazyme PCT and Maglumi PCT with the other methods. Conclusions Although we found acceptable correlation among 10 commercial PCT immunoassays, the limited agreement at clinical decision thresholds remains a major issue, especially at lower end of PCT concentration, thus potentially contributing to jeopardize the clinical value of this biomarker.

Development of a novel chemiluminescence immunoassay for the detection of procalcitonin

OBJECTIVE

To evaluate the analytical performance of our previously developed chemiluminescence immunoassay (CLIA) kit for the detection of procalcitonin (PCT) and compare with the results obtained using the Vidas B.R.A.H.M.S. PCT™ test (PCT-V).

DESIGN AND METHODS

Our laboratory previously designed a novel CLIA kit and supporting instrument (AE-180) for the detection of PCT. We analyzed the clinical performance of this system, including the imprecision, limit of detection, and linearity of analyses of 305 serum specimens. The results were compared with measurements of the same serum samples obtained with PCT-V.

RESULTS

The limit of detection and blank of our kit were 0.0075 and 0.0039 ng/mL, respectively. The intra- and inter-assay coefficient of variation of the kit were both between 0.8% and 3.9%. The equation of linearity was found to be y = 1.03× + 0.06 (r = 0.99) for concentrations in the range of 0.01-110 ng/mL. The correlation coefficient with the results of PCT-V was 0.995, and the equation obtained for Passing and Bablok regression analysis was 1.061 for our CLIA PCT kit and - 0.003 for PCT-V. Our kit slightly overestimated the concentration according to comparison with PCT-V results.

CONCLUSION

The kit that was previously developed in our laboratory for the measurement of serum PCT concentration using CLIA technology shows excellent performance, just that the functional sensitivity is not as good as the PCT-V; therefore, we suggest that this kit is suitable for clinical use.

Analytical Evaluation of the New Beckman Coulter Access Procalcitonin (PCT) Chemiluminescent Immunoassay

This study was designed to evaluate the analytical performance of the recently commercialized Beckman Coulter Access procalcitonin (PCT) chemiluminescent test on the Access immunoassay system. The analytical assessment encompassed the estimation of limit of blank (LoB), limit of detection (LoD), functional sensitivity (i.e., PCT value with ≤10% imprecision), linearity, imprecision and comparability of values with BRAHMS PCT-sensitive Kryptor. LoB, LoD and functional sensitivity were 0.002 μg/L, 0.003 μg/L and 0.003 μg/L, respectively. Intra-assay, inter-assay and total imprecision for plasma pools with low, medium and high PCT values were 1.8–2.1%, 2.4–3.7% and 3.1–4.3%, respectively. The assay exhibited excellent linearity between 0.02 and 84.0 μg/L. Excellent correlation (r = 0.999; p < 0.001) and negligible bias (3.2%) were found by comparing values obtained in paired plasma samples with BRAHMS PCT-sensitive Kryptor. Diagnostic agreement at 0.5, 2.0 and 10 μg/L PCT values ranged between 98%-100%. The results of this study confirm that Access PCT displays excellent analytical performance and high comparability with BRAHMS PCT-sensitive Kryptor.