Practical Laboratory Medicine最新文献

The “hook effect” or “prozone phenomenon” occurs when the concentration of a particular analyte saturates the antibodies used in the test, resulting in falsely low or negative results despite the presence of high analyte concentrations. We report two recent cases of hook effect encountered with a widely used immunoassay analyzer, the Siemens Atellica® IM1600. The first case involves a patient with advanced metastatic prostate cancer whose total PSA (tPSA) concentration dropped dramatically from his last biological control. The second case concerns a pregnant woman whose total HCG (ThCG) levels were also subject to the hook effect and who was found to have a molar pregnancy. In both cases, a dilution step enabled to overcome this analytical concern and to obtain a correct result. In addition, a comparison of the sensitivity of different immunoassay analyzers to this phenomenon was carried out. To avoid this analytical error, an additional dilution step should automatically be performed when there is a clinical suspicion of elevated levels of tumor or hormone markers. Finally, the most affected manufacturers should adapt their assays, accordingly.

Objectives

Point of care testing (POCT) offers the possibility of near bedside patient testing with a reduction of the turn-around time of analysis. The aim of our study was to determine the analytical performances and usability of a recently developed POCT device for the measurement of tests related to liver function. We evaluated the performance of a liver tests panel performed on the LINX EVO® POCT device.

Design and methods

The imprecision was determined with the Bio-Rad Liquichek Unassayed Chemistry Control. Method comparison was performed with a Cobas® 8000 analyzer. Samples from twenty healthy volunteers were used to verify the reference intervals. Furthermore, practicality was assessed by the healthcare staff handling the POCT device through a dedicated questionnaire.

Results

The imprecision observed was matching the criteria for the in-lab assay with only one exception, globulin, with an observed imprecision of 6.3 % and a criteria of 5.7 %. With the exception of total and direct bilirubin, the POCT method showed good agreement with the in-lab methods. The verification of reference intervals showed that more than 90 % of the healthy volunteer values were included into the reference interval claimed by the manufacturer except for glucose and globulin. The POCT practicality questionnaire was satisfying overall for users.

Conclusions

Our study showed very good analytical performances overall for the liver test panel performed on the LINX EVO® POCT instrument.

In Poland, independent evaluations under the auspices of the Institute of Hematology and Transfusion Medicine (IHTM) are mandated for any new device, assay, systems for screening samples from whole blood and plasma donors prior to implementation by Blood Transfusion Center (BTC). In last 5 years, two new systems were introduced to the market by Abbott GmbH, namely the Alinity s and the Alinity i. The evaluations performed for these two systems included the assessment of sensitivity, specificity and precision for each of the four mandatory serological screening markers in Poland: Hepatitis B Surface Antigen (HBsAg), Hepatitis C virus antibodies (Anti-HCV), HIV antibodies (anti-HIV) and Syphilis antibodies (anti-Treponema pallidum, anti-TP). Sensitivity was assessed by testing seroconversion panels, HBsAg international reference standard, well characterized local samples, and dilution panels. Specificity was assessed by testing routine donor samples. The results from Alinity i assays were compared to the results from Abbott ARCHITECT i2000SR and Ortho VITROS 3600 assays, while the results from Alinity s assays were compared to the results of ARCHITECT i2000SR assays. The evaluation of the Alinity s and Alinity i assays for sensitivity (100 %), specificity (99,92–100 %) and precision generated results that were as good as or better than generated by routinely used systems, were within acceptance criteria, and met all requirements for screening blood donor samples in accordance with Polish regulations. The specificity of the assays in routine use by BTCs, analyzed after approximately 150,000 donations on both systems, was comparable to the specificity observed during the evaluations at IHTM.

Introduction

Sodium fluoride/potassium oxalate (NaF/KOx) tubes has been regarded as the gold-standard tubes for glucose analysis. Even though their ineffectiveness in immediately inhibiting glycolysis has been reported in several studies especially in the first 1–4h, they are still used in our clinical biochemistry laboratory for glucose measurement. However, in its absence, only serum separator tubes are employed for glucose measurement. We aim to determine whether serum separator tubes (SSTs) can replace NaF/KOx tubes for laboratory measurement of blood glucose and to assess the stability of glucose concentrations for 3 days period.

Methods and findings

NaF/KOx tube type was the reference method while SSTs type was the candidate method for glucose measurement. A total of 50 paired samples collected separately in NaF/KOx tubes and SSTs from healthy adult participants in the Gambia Adults Reference Intervals Study (GARIS) project were used as the project sample size. Following blood collection and separation, the glucose concentration was measured within 2 h, and at 24h, 42h and 72h time-points. Our data analysis showed no significant difference in the mean glucose concentrations between the reference tube and candidate tube types (Mean difference = 0.06 mmol/L; P = 0.38) recorded in the different timepoints. Using growth trajectory and mixed effects model, the study data further showed no significant change in the glucose concentrations (p = 0.25) for three days period.

Conclusions

The study confirms that SSTs can produce similar glucose results when employed in the absence of NaF/KOx tubes. Besides, the glucose concentrations were stable in both tubes for three days when the samples were separated within 2 h and refrigerated in 2–8°C.

Objective

To develop and validate a rapid liquid chromatography-tandem mass spectrometry (LC-MS/MS) method to detect urinary free metanephrines and methoxytyramine, establishing reference intervals.

Methods

Urine samples were diluted with isotope internal standard solution, then analyzed directly using tandem mass spectrometry with multiple reaction monitoring measurement and electrospray ionization source in positive ion mode. Analytical parameters including linearity, lower limit of quantitation, imprecision and accuracy of the method were evaluated. The reference intervals for urinary catecholamine metabolites were established by analyzing 24-h urine samples collected from 81 apparently healthy volunteers.

Results

The analytical times for MN, NMN, and 3-MT were at 2.79, 2.80, and 2.74 min, respectively. The method displayed excellent linearity (r > 0.99) in the range of 1-1000 ng/mL, with lower limits of quantification (LLOQ) at 0.50 ng/mL for MN and NMN, and 0.25 ng/mL for 3-MT. The method's intra-day and inter-day imprecisions were less than 8 %. The method recovery ranged from 96.8% to 105.8 % for MN, 89.7%–106.4 % for NMN, and 93.5%–106.2 % for 3-MT. No carry-over was observed during the analysis of all analytes. The LC-MS/MS method was used to establish reference intervals in 24-h urine samples from 81 apparently healthy volunteers. There was no association of sex with urinary free metabolites.

Conclusion

This study established a novel, fast and sensitive LC-MS/MS method for determining urinary free catecholamine metabolites, which could facilitate screening and diagnosis for catecholamine-related tumors more conveniently and quickly.

Background

Whether chemiluminescence immunoassay (CLIA) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) for plasma aldosterone concentration (PAC) measurement can be used interchangeably in primary aldosteronism (PA) screening is still controversial. The purpose of this study was to compare CLIA to LC-MS/MS for PAC measurement in PA screening.

Methods

All participants underwent aldosterone-to-renin ratio (ARR) testing. PA was diagnosed by captopril challenge test or saline infusion test. PAC in screening test was measured with CLIA and LC-MS/MS. Plasma direct renin concentration in screening and confirmatory test was measured with CLIA. The concordance between CLIA and LC-MS/MS for PAC measurement in PA screening was analyzed.

Results

Twenty-one healthy volunteers, 61 patients with essential hypertension (EH) and 43 PA patients were enrolled. Median PAC by CLIA was 84.7 % higher than that by LC-MS/MS in screening test (P < 0.001). A positive correlation of PAC was observed between the two assays (Pearson r coefficient 0.770, P < 0.001). When ARR was used in differentiating PA from EH, there was no difference in the area under the receiver operating characteristic curve between CLIA and LC-MS/MS for PAC measurement (0.968 vs 0.950, P = 0.249).

Conclusion

CLIA and LC-MS/MS for PAC measurement exhibited high and comparable efficacy in PA screening. CLIA is a reliable and feasible alternative in PA screening test.

Background

Preeclampsia is a kind of pregnancy-related hypertension that affects 5.47 % of pregnancies in Ethiopia and 18.25 % of pregnant women who visit Arba Minch public health facilities for antenatal care. This study sought to identify hematological preeclampsia markers in pregnant women who received prenatal care at Arba Minch General Hospital.

Methodology

An institution-based comparative cross-sectional study was done from July 22 to October 30, 2021 at Arba Minch General Hospital. A total of 136 pregnant women were included in the study (46 with preeclampsia and 90 without preeclampsia). Epidata version 4.4. was used to enter data, and SPSS version 25.0 and Stata version17 were used for analysis. An independent sample t-test was used to examine the hematological parameter differences between study groups. Potential hematological markers were determined using receiver operating characteristic (ROC) analysis of the area under the curve (AUC). Statistical significance was defined if P value less than 0.05.

Results

A total of 136 pregnant women were studied. The complete blood count analysis showed that there were means differences in Red Cell Distribution (RDW) (p < 0.036), neutrophil-to-lymphocyte ratio (NLR) (p < 0.016) and relative lymphocyte count (Lymp%) (p < 0.047). The ROC analysis of the AUC for RDW, NLR and Lymp% resulted in 0.607, 0.609, 0.600 respectively.

Conclusion

RDW, NLR and Lymphocyte count could be potential candidate tools for the diagnosis and screening of preeclampsia. However, the robustness of the markers should be tested with prospective studies assessing changes present in each trimester.

Objectives

Both dimethylarginines are widely bound to chronic kidney disease (CKD). This study was focused to validate published LC-MS/MS method and compared the measured data with an immunoassay.

Design and methods

The analysis was performed on a Dionex UltiMate 3000 UHPLC-Standard (Thermo Fisher Scientific, Waltham, Massachusetts, USA) with an amaZon SL ion trap (Bruker, Billerica, Massachusetts, USA). Comparison was evaluated by using Passing Bablok regression and Bland Altman plot. Healthy volunteers (n = 40) were used for validation and as control group to patients group (n = 40) with different stages of CKD.

Results

The results in healthy controls determined by the LC-MS/MS (ELISA) method were 0.52 ± 0.0892 with 95 % CI: 0.49–0.55 (0.61 ± 0.1213 with 95 % CI: 0.57–0.64) μmol/L for AD MA and 0.56 ± 0.0810 with 95 % CI: 0.53–0.58 (0.62 ± 0.0752 with 95 % CI: 0.57–0.65) μmol/L for SDMA. In the same way, the patient group values determined by the LC-MS/MS (ELISA) method were 0.82 ± 0.1604 with 95 % CI: 0.75–0.88 (1.06 ± 0.3002 with 95 % CI: 0.94–1.19) μmol/L and 2.14 ± 0.8778 with 95 % CI: 1.47–2.58 (1.65 ± 0.5160 with 95 % CI: 1.40–1.98) μmol/L for ADMA and SDMA, respectively. The correlation between the methods, expressed as the Spearman correlation coefficient (R), was 0.858 (0.8059) for ADMA (p < 0.0001) and 0.895 (0.9607) for SDMA (p < 0.0001).

Conclusions

ADMA levels determined by the immunoassay were almost 30 % overestimated, in contrast to SDMA levels, which were 3 % underestimated. According to our findings, a better correlation could be obtained by simple sample dilution.

Reporting a measurement procedure and its analytical performance following method evaluation in a peer-reviewed journal is an important means for clinical laboratory practitioners to share their findings. It also represents an important source of evidence base to help others make informed decisions about their practice. At present, there are significant variations in the information reported in laboratory medicine journal publications describing the analytical performance of measurement procedures. These variations also challenge authors, readers, reviewers, and editors in deciding the quality of a submitted manuscript.

The International Federation of Clinical Chemistry and Laboratory Medicine Working Group on Method Evaluation Protocols (IFCC WG-MEP) developed a checklist and recommends its adoption to enable a consistent approach to reporting method evaluation and analytical performance characteristics of measurement procedures in laboratory medicine journals. It is envisioned that the LEAP checklist will improve the standardisation of journal publications describing method evaluation and analytical performance characteristics, improving the quality of the evidence base that is relied upon by practitioners.

Objectives

Soluble B-Cell Maturation Antigen (sBCMA) is a degradation product of plasma cell-bound BCMA found in serum. Serum sBCMA concentrations correlate with bone marrow plasma cellularity, making it an attractive biomarker for monitoring plasma cell disorders, such as multiple myeloma. Here we evaluated the automated BCMA immunoassay for the ProteinSimple ELLA, for the analysis of sBCMA.

Design & methods

Inter and intra-run precision was assessed through replicate sBCMA measurements at 3 different concentration levels. Linearity was determined through serial dilution of a high sBMCA patient sample. Accuracy was assessed through split specimen analysis on two separate lots of reagents. Stability was assessed at 3 temperature levels over 14 days. Cross-reactivity was assessed on BCMA targeting and non-targeting chemotherapeutics. A reference range was established through the analysis of 146 healthy donor samples. The effect of endogenous interferents was assessed through spiking and recovery studies.

Results

Inter and intra-run precision studies afforded CVs of <10% at all three concentration levels. Analytical measurement range was confirmed from 0.1 to 7 ng/mL. Accuracy studies afforded a slope of 0.976, intercept of 1.22, R² of 0.996. Assayed sBCMA values were unaffected by endogenous interferents and non-BMCA targeting antibodies. BCMA targeting therapeutics negatively affected assayed sBCMA concentrations. The reference range was established at 19–58 ng/mL sBCMA is analytically stable.

Conclusions

The ProteinSimple ELLA sBCMA assay shows acceptable performance for the clinical assessment of sBCMA. The assay was highly affected by BCMA targeting therapeutics, thereby patients undergoing this therapy should not have their sBCMA levels assessed by this method.