Detection of Bacterial Infection Based on Age-Specific Percentile-Based Reference Curve for Serum Procalcitonin Level in Preterm Infants.

BACKGROUND: Considering the physiological changes in serum procalcitonin (PCT) levels in newborns due to age, we recently established an age-specific percentile-based reference curve for serum PCT level. The present study aimed to determine the best cutoff percentile line using this reference curve for the differentiation between infected and colonized preterm infants. METHODS: A total of 52 preterm infants with positive bacterial culture (9 with bacterial infection, 43 with colonization) were enrolled within the study period. The 97.5th, 95.0th, 92.5th, 90.0th, 80.0th, 70.0th, 60.0th, and 50.0th percentile lines were drawn in the reference curve. PCT levels in infected or colonized infants were used, and sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated. The best cutoff percentile line was determined in the receiver operating characteristic curve analysis. RESULTS: Of the 52 preterm infants, 9 were infected (5 and 4 infants with an onset of < 7 days and ≥ 7 days after birth, respectively), whereas 43 were colonized (6 and 37 infants with an onset of < 7 days and ≥ 7 days after birth, respectively). The best cutoff percentile lines were the 90.0th percentile (sensitivity, 0.800; specificity, 0.833; PPV, 0.800; NPV, 0.833) and 97.5th percentile (sensitivity, 1.00; specificity, 0.973; PPV, 0.800; NPV, 1.00) in infants with an onset of < 7 days and ≥ 7 days after birth, respectively. CONCLUSIONS: The age-specific percentile-based reference curve for serum PCT level is clinically applicable as a new tool for diagnosing infections in preterm infants with positive culture results, particularly at ≥ 7 days after birth.

[Performance Utility of High Sensitivity Quantitative Assay for HBs Antigen].

A high sensitivity quantitative assay for hepatitis B virus (HBV) surface antigen (HBsAg-HQ assay) was recently developed and is useful for earlier detection of HBV reactivation. We created HBsAg-HQ assay operational proce- dures by the sample transport system and laboratory information system. In this study, we evaluated the perfor- mance and utility of the HBsAg-HQ assay based on our operational procedures using internal quality control (IQC) data and 13,762 samples routinely measured for 8 months. The IQC data of the HBsAg-HQ assay demonstrated good accuracy (CV: 1.6-2.7%). The difference in IQC data between two of the same analyzers or several reagent lots had no clinical significance. Of 13,762 samples, HBsAg titer was negative in 12,592(91.5%) and positive in 1,169(8.5%), and HBsAg negative samples were remarkably lower(<0.001 IU/mL) than the cut-off value(0.005 IU/mL). Among 114 HBsAg weakly positive samples ranging from 0.005 to 1.000 IU/mL, false positive results occurred in 12 samples, which were converted into negative results after re-measurement. We could effectively perform carry-over prevention and dilution of high titer samples using our operational procedures. Furthermore, we performed inhibition test in 52 HBsAg weakly positive samples, and 20 samples, most of which were taken from patients with connective tissue disease or malignancy, were judged as non-specific reactivity. Taken together, our operational HBsAg-HQ assay procedures may contribute to efficient workflow for routine testing. Moreover, the HBsAg-HQ assay may be clinically useful for not only highly sensitive assays, but also for reducing false positives.

Age-specific percentile-based reference curve of serum procalcitonin concentrations in Japanese preterm infants.

Procalcitonin (PCT) levels are elevated early after birth in newborn infants; however, the physiological features and reference of serum PCT concentrations have not been fully studied in preterm infants. The aims of the current study were to establish an age-specific percentile-based reference curve of serum PCT concentrations in preterm infants and determine the features. The PCT concentration peaked in infants at 1 day old and decreased thereafter. At 1 day old, serum PCT concentrations in preterm infants <34 weeks' gestational age were higher than those in late preterm infants between 34 and 36 weeks' gestational age or term infants ≥37 weeks' gestational age. Although the 50-percentile value in late preterm and term infants reached the adult normal level (0.1 ng/mL) at 5 days old, it did not in preterm infants. It took 9 weeks for preterm infants to reach it. Serum PCT concentrations at onset in late-onset infected preterm infants were over the 95-percentile value. We showed that the physiological feature in preterm infants was significantly different from that in late preterm infants, even in those <37 weeks' gestational age. To detect late-onset bacterial infection and sepsis, an age-specific percentile-based reference curve may be useful in preterm infants.

[Evaluation of cut-off value for autoantibodies against double-stranded DNA-complexed nucleosomes based on enzyme linked immunosorbent assay].

The new classification criteria for systemic lupus erythematosus (SLE) by Systemic Lupus International Collaborating Clinics (SLICC) published in 2012 have defined positive level titer of antibody against double stranded (ds) DNA as more than double the reference range if tested by enzyme linked immunosorbent assay (ELISA). The aim of this study was to evaluate optimal cut-off value and diagnostic performance of the anti-dsDNA nucleosome-complexed (anti-dsDNA-NcX) ELISA, which uses salmon testis DNA complexed with purified nucleosomes as antigens, for diagnosis of SLE. Titers of antibodies against dsDNA-complexed nucleosome were measured in sera of 76 patients with SLE, 148 with other connective tissue diseases, and 323 healthy volunteers. Sensitivity, specificity, correlation and concordance rate were compared among anti-dsDNA-NcX, conventional ELISA methods (EIA) and radioimmunoassay (RIA). As a results, concordance rates and Spearman's coefficient of rank correlation (r(s)) of anti-dsDNA-NcX with EIA and RIA were 59.2%, r(s) = 0.40 and 53.9%, r(s) = 0.21, respectively. Receiver operating characteristic curve analysis showed that the titer of 44 IU/mL calculated as 99 percentile of 323 healthy volunteers is a better cut-off value for anti-dsDNA-NcX than the 100 IU/mL recommended by the manufacturer. By setting the cut-off value at 44 IU/mL, anti-dsDNA-NcX showed the highest sensitivity (75.0%) and specificity (90.5%) of the 3 assays. With SLICC criterion, positivity rates of anti-dsDNA-NcX, EIA and RIA for SLE patients were 50.0%, 30.3% and 50.0%, respectively. In conclusion, anti-dsDNA-NcX has a good diagnostic performance for SLE with our proposed cut-off value of 44 IU/mL.

[Usefulness of anti-SS-A/Ro antibody measurement based on fluorescence enzyme immunoassay with Ro60 and Ro52 antigen].

OBJECTIVE: Anti-SS-A/Ro antibody is commonly found in the sera of patients with rheumatic disease. The antigenic components of SS-A/Ro are 60kD. and 52kD-Ro protein. Only anti-60kD SS-A/Ro antibody is detected by commonly used tests in clinical laboratories. "UniCAP EliA SS-A/Ro" is a new reagent using fluorescence enzyme immunoassay (FEIA) based on a mixture of both 60kD- and 52kD-Ro antigens. We evaluated the efficacy of detecting both anti-60kD and 52kD SS-A/Ro antibodies. PATIENTS AND METHODS: We collected sera from 264 rheumatic disease patients and 106 healthy subjects. Anti-SS-A/Ro antibodies were measured by the new reagent along with conventional method. Anti-52kD and 60kD SS-A/Ro antibodies were measured by ELISA kit in rheumatic disease patients. RESULTS: Anti-SS-A/Ro antibody levels were higher in patients with Sjögren's syndrome than those with SLE or RA. The prevalence of anti-SS-A/Ro antibody in rheumatic disease patients and healthy subjects were comparable with the conventional method, and patients with Sjögren's syndrome had highest prevalence of anti-SS-A/Ro antibody. Concordance rate between EliA and conventional method, and EliA and DID, were 96.6% and 94.3%, respectively. ELISA analysis revealed that patients with Sjögren's syndrome had anti-52kD SS-A/Ro antibody at high rates, while anti-60kD SS-A/Ro antibody was widely found in rheumatic disease patients. Three patients were positive only for anti-52kD SS-A/Ro antibody. CONCLUSION: Taken together, "UniCAP EliA SS-A/Ro" is useful as a screening test for anti-SS-A/Ro antibodies.