Darci R. Block

Body fluid analysis: Clinical utility and applicability of published studies to guide interpretation of today’s laboratory testing in serous fluids

Abstract Requests for testing various analytes in serous fluids (e.g. pleural, peritoneal, pericardial effusions) are submitted daily to clinical laboratories. Testing of these fluids deviates from assay manufacturers’ specifications, as most laboratory assays are optimized for testing blood or urine specimens. These requests add a burden to clinical laboratories, which need to validate assay performance characteristics in these fluids to exclude matrix interferences (given the different composition of body fluids) while maintaining regulatory compliance. Body fluid testing for a number of analytes has been reported in the literature; however, understanding the clinical utility of these analytes is critical because laboratories must address the analytic and clinical validation requirements, while educating clinicians on proper test utilization. In this article, we review the published data to evaluate the clinical utility of testing for numerous analytes in body fluid specimens. We also highlight the pre-analytic and analytic variables that need to be considered when reviewing published studies in body fluid testing. Finally, we provide guidance on how published studies might (or might not) guide interpretation of test results in today’s clinical laboratories.

Local verification and assignment of mean normal prothrombin time and International Sensitivity Index values across various instruments: recent experience and outcome from North America.

Warfarin dosing relies on accurate measurements of international normalized ratio (INR), which is calculated from the prothrombin time (PT), International Sensitivity Index international sensitivity index (ISI) of the thromboplastin, and the geometric mean of normal PT (MNPT). However, ISI assignments of certain reagent/instrument combinations are frequently unavailable, especially when the reagent and instrument are not from the same manufacturer. The effort to be in compliance with widely endorsed Clinical and Laboratory Standards Institute (CLSI) guidelines by locally verifying or assigning an ISI to an unsupported reagent/instrument combination is further hindered by the lack of US Food and Drug Administration (FDA)-approved certified plasmas designated for a particular reagent/instrument combination. The objectives of the study include development of a process to verify/assign ISI and MNPT of a single thromboplastin reagent from one manufacturer across multiple instruments including several from another manufacturer and across several campuses of a single institution, the Mayo Clinic. In this study, RecombiPlasTin 2G (R2G), was evaluated on the ACL TOP 700 (IL), STA-R Evolution, STA Compact, and STA Satellite. Random normal donor samples (n = 25) were used to verify/assign MNPT. A subset of the normal donors (n = 8) and 13 warfarin pools (INR range: 1.3-3.9), created from stable warfarin patient plasma, were used for ISI verification/assignment. The manufacturers assigned ISI was first verified on the ACL TOP 700 (reference method), then assigned on three unsupported instruments using orthogonal regression analysis. The MNPT and manufacturer assigned ISI (11.0, 0.95) were verified on the ACL TOP 700 and subsequently assigned on the STA-R Evolution (11.6, 1.04); STA Compact (11.5, 1.02); and STA Satellite (10.9, 0.99). Linear correlations of the INR results from all the four instruments demonstrated an r2 > 0.99. This process provides a reproducible approach to assigning ISIs on unsupported reagent/instrument combinations. Our data also confirm that ISIs of the same PT reagent differ significantly on different instruments, thus confirming the requirement for evaluations and validation of ISIs for different reagent/instrument combinations.

Implementation of Clinical Decision Support Rules to Reduce Repeat Measurement of Serum Ionized Calcium, Serum Magnesium, and N-Terminal Pro-B-Type Natriuretic Peptide in Intensive Care Unit Inpatients

BACKGROUND We assessed the impact of clinical decision support (CDS) rules within the electronic health record for ionized calcium (iCa), serum magnesium (Mg), and N-terminal pro-B-type natriuretic peptide (NT-proBNP) in intensive care unit (ICU) inpatients at a large academic center. METHODS A repeat order for measurement of iCa or Mg placed within 24 (iCa) or 48 (Mg) h of a previously nonactionable result, or additional orders for NT-proBNP beyond 1 within a single hospitalization, triggered a CDS pop-up alert showing the prior result and offering the opportunity to cancel the order or to place the order after entering an indication for repeat testing. The number of tests performed for each of these analytes and incidence of adverse clinical outcomes potentially associated with hypocalcemia or hypomagnesemia were compared between the 90-day period before CDS implementation and two 90-day periods immediately following. RESULTS iCa test volumes decreased by 48%, Mg by 39%, and NT-proBNP by 28% in the 90-day period immediately following implementation and remained decreased by 54%, 49%, and 22%, respectively, during the following 90-day period (all P values <0.0002). Adverse clinical outcomes potentially associated with hypocalcemia or hypomagnesemia did not increase (all P-values >0.17). CONCLUSIONS Implementation of CDS dramatically decreased repeat testing of iCa, Mg, and NT-proBNP without adversely impacting clinical outcomes in the ICU. Expansion of the rules from the ICU units to include the entire hospitalized patient population and expansion to additional analytes is expected to lead to further reductions in testing.

Evaluation of Beckman Coulter DxI 800 immunoassay system using clinically oriented performance goals.

OBJECTIVES We evaluated the analytical performance of 24 immunoassays using the Beckman Coulter DxI 800 immunoassay systems at Mayo Clinic, Rochester, MN for trueness, precision, detection limits, linearity, and consistency (across instruments and reagent lots). METHODS Clinically oriented performance goals were defined using the following methods: trueness-published desirable accuracy limits, precision-published desirable biologic variation; detection limits - 0.1 percentile of patient test values, linearity - 50% of total error, and consistency-percentage test values crossing key decision points. Local data were collected for precision, linearity, and consistency. Data were provided by Beckman Coulter, Inc. for trueness and detection limits. RESULTS All evaluated assays except total thyroxine were within the proposed goals for trueness. Most of the assays met the proposed goals for precision (86% of intra-assay results and 75% of inter-assay results). Five assays had more than 15% of the test results below the minimum detection limits. Carcinoembryonic antigen, total thyroxine and free triiodothyronine exceeded the proposed goals of ±6.3%, ±5% and ±5.7% for dilution linearity. All evaluated assays were within the proposed goals for instrument consistency. Lot-to-lot consistency results for cortisol, ferritin and total thyroxine exceeded the proposed goals of 3.3%, 11.4% and 7% at one medical decision level, while vitamin B12 exceeded the proposed goals of 5.2% and 3.8% at two decision levels. CONCLUSIONS The Beckman Coulter DxI 800 immunoassay system meets most of these proposed goals, even though these clinically focused performance goals represent relatively stringent limits.

Analytical and clinical comparison of anti-CCP assays with rheumatoid factor for the diagnosis of rheumatoid arthritis

INTRODUCTION Rheumatoid arthritis (RA) is an inflammatory autoimmune disease characterized by chronic joint inflammation and extra-articular manifestations, eventually leading to permanent disability without early therapeutic interventions. METHODS The analytical and clinical performance of an electrochemiluminescent immunoassay (ECLIA) (Roche Diagnostics, Indianapolis, IN) were determined for cyclic citrullinated peptide antibodies (anti-CCP) in the diagnostic assessment of rheumatoid arthritis compared to a plate-based anti-CCP enzyme immunoassay (EIA) (Inova Diagnostics, Inc.). RESULTS Imprecision studies on the automated Roche ECLIA demonstrated intra-assay CVs of <3% and inter-assay CVs of <7%. The Inova EIA had intra-assay CVs of <15% and inter-assay CVs of <12%. The limit of quantitation of both assays was acceptable, and both assays showed similar linearity within the manufacturers defined reportable ranges. Overall, analytical concordance was 62%, with 95.2% positive and 53.2% negative concordance. The clinical specificity in a normal population (n=91) was 98.9% and 100% for Roche ECLIA and Inova EIA, respectively. The clinical specificity in a connective tissue disease population (n=98) was 91.9% (95%CI, 86.0 to 96.5%) and 88.8% (95% CI, 81.0 to 93.6%) for Roche ECLIA and Inova EIA, respectively. CONCLUSION The Roche ECLIA demonstrated similar analytical performance, although with improved intra-assay precision, in comparison to the Inova EIA. The two methods also demonstrated similar clinical sensitivity and specificity. The Roche automated immunoassay is a viable alternative to the plate-based EIAs with the advantage of being performed on an automated platform.

Ureaplasma urealyticum Causes Hyperammonemia in an Experimental Immunocompromised Murine Model.

Hyperammonemia syndrome is an often fatal complication of lung transplantation which has been recently associated with Ureaplasma infection. It has not been definitely established that Ureaplasma species can cause hyperammonemia. We established a novel immunocompromised murine model of Ureaplasma urealyticum infection and used it to confirm that U. urealyticum can cause hyperammonemia. Male C3H mice were pharmacologically immunosuppressed with mycophenolate mofetil, tacrolimus and oral prednisone for seven days, and then challenged intratracheally (IT) and/or intraperitoneally (IP) with 107 CFU U. urealyticum over six days, while continuing immunosuppression. Spent U. urealyticum-free U9 broth was used as a negative control, with uninfected immunocompetent mice, uninfected immunosuppressed mice, and infected immunocompetent mice serving as additional controls. Plasma ammonia concentrations were compared using Wilcoxon ranks sum tests. Plasma ammonia concentrations of immunosuppressed mice challenged IT/IP with spent U9 broth (n = 14) (range 155–330 μmol/L) were similar to those of normal mice (n = 5), uninfected immunosuppressed mice (n = 5), and U. urealyticum IT/IP challenged immunocompetent mice (n = 5) [range 99–340 μmol/L, p = 0.60]. However, immunosuppressed mice challenged with U. urealyticum IT/IP (n = 20) or IP (n = 15) had higher plasma ammonia concentrations (range 225–945 μmol/L and 276–687 μmol/L, respectively) than those challenged IT/IP with spent U9 broth (p<0.001). U. urealyticum administered IT/IP or IP causes hyperammonemia in mice pharmacologically immunosuppressed with a regimen similar to that administered to lung transplant recipients.

A Case of Floating Gel

Two unrelated patients underwent coronary angiography and a percutaneous intervention. At the end of the procedures, blood was collected (Vacutainer® SST™; BD) for troponin, creatine kinase (CK), and CK-MB isoenzyme analysis. After centrifugation with the Roche Modular Pre-Analytics system (Roche Diagnostics), pipetting error alerts were triggered on the aliquoting module of the Pre-Analytics system. Investigation revealed that the separator gel had migrated above the serum (Fig. 1A), preventing separation of the serum from the …

Evaluation of lactate, white blood cell count, neutrophil count, procalcitonin and immature granulocyte count as biomarkers for sepsis in emergency department patients

BACKGROUND Lactate, white blood cell (WBC) and neutrophil count, procalcitonin and immature granulocyte (IG) count were compared for the prediction of sepsis, and severe sepsis or septic shock, in patients presenting to the emergency department (ED). METHODS We prospectively enrolled 501 ED patients with a sepsis panel ordered for suspicion of sepsis. WBC, neutrophil, and IG counts were measured on a Sysmex XT-2000i analyzer. Lactate was measured by i-STAT, and procalcitonin by Brahms Kryptor. We classified patients as having sepsis using a simplification of the 1992 consensus conference sepsis definitions. Patients with sepsis were further classified as having severe sepsis or septic shock using established criteria. Univariate receiver operating characteristic (ROC) analysis was performed to determine odds ratio (OR), area under the ROC curve (AUC), and sensitivity/specificity at optimal cut-off for prediction of sepsis (vs. no sepsis), and prediction of severe sepsis or septic shock (vs. no sepsis). RESULTS There were 267 patients without sepsis; and 234 with sepsis, including 35 patients with severe sepsis or septic shock. Lactate had the highest OR (1.44, 95th% CI 1.20-1.73) for the prediction of sepsis; while WBC, neutrophil count and percent (neutrophil/WBC) had OR>1.00 (p<0.05). All biomarkers had AUC<0.70 and sensitivity and specificity <70% at the optimal cut-off. Initial lactate was the best biomarker for predicting severe sepsis or septic shock, with an odds ratio (95th% CI) of 2.70 (2.02-3.61) and AUC 0.89 (0.82-0.96). CONCLUSION Traditional biomarkers (lactate, WBC, neutrophil count, procalcitonin, IG) have limited utility in the prediction of sepsis.

Diagnostic accuracy and clinical relevance of an inflammatory biomarker panel for sepsis in adult critically ill patients.

The objective of this study was to assess the diagnostic accuracy of C-reactive protein (CRP), procalcitonin (PCT), and cellular immune markers levels in sepsis. This was a prospective observational study in adult intensive care unit (ICU) patients, between 2012 and 2014. The 8-color flow cytometric biomarker panel included CD64, CD163, and HLA-DR. Index test results were compared with sepsis, using receiver operating characteristic curve analyses. Multivariate logistic regression assessed the relationship of sets of markers with the probability of sepsis. Of 219 enrolled patients, 120 had sepsis. C-statistic was the highest for CRP (0.86) followed by neutrophil CD64 expression (0.83), procalcitonin (0.82), and Acute Physiology and Chronic Health Evaluation (APACHE) IV (0.72). After adjustment for APACHE IV, the combination of CRP, PCT, and neutrophil CD64 measure remained a significant predictor of sepsis with an excellent AUC (0.90). In a targeted ICU population at increased risk of sepsis, CRP, PCT, and neutrophil CD64 combined improve the diagnostic accuracy of sepsis.

Fecal electrolyte testing for evaluation of unexplained diarrhea: Validation of body fluid test accuracy in the absence of a reference method

BACKGROUND Validation of tests performed on body fluids other than blood or urine can be challenging due to the lack of a reference method to confirm accuracy. The aim of this study was to evaluate alternate assessments of accuracy that laboratories can rely on to validate body fluid tests in the absence of a reference method using the example of sodium (Na(+)), potassium (K(+)), and magnesium (Mg(2+)) testing in stool fluid. METHODS Validations of fecal Na(+), K(+), and Mg(2+) were performed on the Roche cobas 6000 c501 (Roche Diagnostics) using residual stool specimens submitted for clinical testing. Spiked recovery, mixing studies, and serial dilutions were performed and % recovery of each analyte was calculated to assess accuracy. Results were confirmed by comparison to a reference method (ICP-OES, PerkinElmer). RESULTS Mean recoveries for fecal electrolytes were Na(+) upon spiking=92%, mixing=104%, and dilution=105%; K(+) upon spiking=94%, mixing=96%, and dilution=100%; and Mg(2+) upon spiking=93%, mixing=98%, and dilution=100%. When autoanalyzer results were compared to reference ICP-OES results, Na(+) had a slope=0.94, intercept=4.1, and R(2)=0.99; K(+) had a slope=0.99, intercept=0.7, and R(2)=0.99; and Mg(2+) had a slope=0.91, intercept=-4.6, and R(2)=0.91. Calculated osmotic gap using both methods were highly correlated with slope=0.95, intercept=4.5, and R(2)=0.97. Acid pretreatment increased magnesium recovery from a subset of clinical specimens. CONCLUSIONS A combination of mixing, spiking, and dilution recovery experiments are an acceptable surrogate for assessing accuracy in body fluid validations in the absence of a reference method.