Amy B. Karger

GFR Estimation Using β-Trace Protein and β2-Microglobulin in CKD

BACKGROUND β-Trace protein (BTP) and β2-microglobulin (B2M) are novel glomerular filtration markers that have stronger associations with adverse outcomes than creatinine. Comparisons of BTP and B2M to creatinine and cystatin C are limited by the absence of rigorously developed glomerular filtration rate (GFR) estimating equations for the novel markers. STUDY DESIGN Study of diagnostic test accuracy. SETTING & PARTICIPANTS Pooled database of 3 populations with chronic kidney disease (CKD) with mean measured GFR of 48 mL/min/1.73 m2 (N=3,551; MDRD [Modification of Diet in Renal Disease] Study, AASK [African American Study of Kidney Disease and Hypertension], and CRIC [Chronic Renal Insufficiency Cohort] Study). INDEX TESTS GFR estimated using creatinine, cystatin C, BTP, or B2M level. REFERENCE TEST GFR measured as the urinary clearance of iothalamate. RESULTS For BTP and B2M, coefficients for age, sex, and race were smaller than for creatinine and were similar or smaller than for cystatin C. For B2M, coefficients for sex, age, and race were smaller than for creatinine and were similar (age and race) or smaller (sex) than for cystatin C. The final equations with BTP (BTP, age, and sex) or B2M (B2M alone) were less accurate than either the CKD-EPI (CKD Epidemiology Collaboration) creatinine or cystatin C equations. The combined BTP-B2M equation (BTP and B2M alone) had similar accuracy to the CKD-EPI creatinine or cystatin C equation. The average of the BTP-B2M equation and the CKD-EPI creatinine-cystatin C equation was not more accurate than the CKD-EPI creatinine-cystatin C equation. LIMITATIONS No external validation population, study population was restricted to CKD, few participants older than 65 years, or nonblack nonwhite race. CONCLUSIONS BTP and B2M are less influenced by age, sex, and race than creatinine and less influenced by race than cystatin C, but provide less accurate GFR estimates than the CKD-EPI creatinine and cystatin C equations. The CKD-EPI BTP and B2M equation provides a methodological advance for their study as filtration markers and in their associations with risk and adverse outcomes, but further study is required before clinical use.

Quantitative Epstein–Barr virus shedding and its correlation with the risk of post-transplant lymphoproliferative disorder

We postulated that quantitative monitoring of Epstein–Barr virus (EBV) shedding after transplantation could distinguish EBV‐associated illnesses and predict clinical outcome. EBV DNA was measured in solid organ (SOT) and hematopoietic cell transplants (HCT) using our own real‐time TaqMan EBV PCR. The proportion of patients who had EBV DNAemia post‐transplant was significantly lower in HCT vs. SOT (p < 0.001). Over a 7.5‐yr period, post‐transplant lymphoproliferative disorder (PTLD) occurred in 66 (5.8%) of 1131 patients who met adequate monitoring criteria. SOT recipients developed PTLD significantly later than HCT recipients (median, 2.8 yr vs. 121 d; p < 0.001). PTLD was documented in 53 (14%) of 376 patients who had EBV in ≥1 whole blood sample vs. 13 (2%) of 755 patients who had at least three EBV‐negative blood samples and were never positive. PTLD risk in viremic patients increased with the peak quantity of EBV DNAemia (p < 0.001). PTLD occurred in 37/333 (11%) of patients with peak blood levels 103–105 copies/mL vs. 16/43 (37%) of patients with levels >105 (p < 0.001). EBV PCR was predictive in 29 (78%) of 37 patients tested within three wk prior to tissue diagnosis of PTLD, and thus, we conclude that EBV PCR with careful attention paid to changes in EBV DNAemia could lead to earlier diagnosis and treatment of PTLD.

Performance in Measurement of Serum Cystatin C by Laboratories Participating in the College of American Pathologists 2014 CYS Survey

CONTEXT Cystatin C is becoming an increasingly popular biomarker for estimating glomerular filtration rate, and accurate measurements of cystatin C concentrations are necessary for accurate estimates of glomerular filtration rate. OBJECTIVE To assess the accuracy of cystatin C concentration measurements in laboratories participating in the College of American Pathologists CYS Survey. DESIGN Two fresh frozen serum pools, the first from apparently healthy donors and the second from patients with chronic kidney disease, were prepared and distributed to laboratories participating in the CYS Survey along with the 2 usual processed human plasma samples. Target values were established for each pool by using 2 immunoassays and ERM DA471/IFCC international reference material. RESULTS For the normal fresh frozen pool (ERM-DA471/IFCC-traceable target of 0.960 mg/L), the all-method mean (SD, % coefficient of variation [CV]) reported by all of the 123 reporting laboratories was 0.894 mg/L (0.128 mg/L, 14.3%). For the chronic kidney disease pool (ERM-DA471/IFCC-traceable target of 2.37 mg/L), the all-method mean (SD, %CV) was 2.258 mg/L (0.288 mg/L, 12.8%). There were substantial method-specific biases (mean milligram per liter reported for the normal pool was 0.780 for Siemens, 0.870 for Gentian, 0.967 for Roche, 1.061 for Diazyme, and 0.970 for other/not specified reagents; and mean milligram per liter reported for the chronic kidney disease pool was 2.052 for Siemens, 2.312 for Gentian, 2.247 for Roche, 2.909 for Diazyme, and 2.413 for other/not specified reagents). CONCLUSIONS Manufacturers need to improve the accuracy of cystatin C measurement procedures if cystatin C is to achieve its full potential as a biomarker for estimating glomerular filtration rate.

Association of biotin ingestion with performance of hormone and nonhormone assays in healthy adults

Importance Biotinylated antibodies and analogues, with their strong binding to streptavidin, are used in many clinical laboratory tests. Excess biotin in blood due to supplemental biotin ingestion may affect biotin-streptavidin binding, leading to potential clinical misinterpretation. However, the degree of interference remains undefined in healthy adults. Objective To assess performance of specific biotinylated immunoassays after 7 days of ingesting 10 mg/d of biotin, a dose common in over-the-counter supplements for healthy adults. Design, Setting, and Participants Nonrandomized crossover trial involving 6 healthy adults who were treated at an academic medical center research laboratory Exposure Administration of 10 mg/d of biotin supplementation for 7 days. Main Outcomes and Measures Analyte concentrations were compared with baseline (day 0) measures on the seventh day of biotin treatment and 7 days after treatment had stopped (day 14). The 11 analytes included 9 hormones (ie, thyroid-stimulating hormone, total thyroxine, total triiodothyronine, free thyroxine, free triiodothyronine, parathyroid hormone, prolactin, N-terminal pro-brain natriuretic peptide, 25-hydroxyvitamin D) and 2 nonhormones (prostate-specific antigen and ferritin). A total of 37 immunoassays for the 11 analytes were evaluated on 4 diagnostic systems, including 23 assays that incorporated biotin and streptavidin components and 14 assays that did not include biotin and streptavidin components and served as negative controls. Results Among the 2 women and 4 men (mean age, 38 years [range, 31-45 years]) who took 10 mg/d of biotin for 7 days, biotin ingestion–associated interference was found in 9 of the 23 (39%) biotinylated assays compared with none of the 14 nonbiotinylated assays (P = .007). Results from 5 of 8 biotinylated (63%) competitive immunoassays tested falsely high and results from 4 out of 15 (27%) biotinylated sandwich immunoassays tested falsely low. Conclusions and Relevance In this preliminary study of 6 healthy adult participants and 11 hormone and nonhormone analytes measured by 37 immunoassays, ingesting 10 mg/d of biotin for 1 week was associated with potentially clinically important assay interference in some but not all biotinylated assays studied. These findings should be considered for patients taking biotin supplements before ordering blood tests or when interpreting results. Trial Registration clinicaltrials.gov Identifier: NCT03034707

Filtration Markers as Predictors of ESRD and Mortality: Individual Participant Data Meta-Analysis

BACKGROUND AND OBJECTIVES Serum β-trace protein (BTP) and β-2 microglobulin (B2M) are associated with risk of ESRD and death in the general population and in populations at high risk for these outcomes (GP/HR) and those with CKD, but results differ among studies. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS We performed an individual patient-level meta-analysis including three GP/HR studies (n=17,903 participants) and three CKD studies (n=5415). We compared associations, risk prediction, and improvement in reclassification of eGFR using BTP (eGFRBTP) and B2M (eGFRB2M) alone and the average (eGFRavg) of eGFRBTP, eGFRB2M, creatinine (eGFRcr), and cystatin C (eGFRcys), to eGFRcr, eGFRcys, and their combination (eGFRcr-cys) for ESRD (2075 events) and death (7275 events). RESULTS Mean (SD) follow up times for ESRD and mortality for GP/HR and CKD studies were 13 (4), 6.2 (3.2), 14 (5), and 7.5 (3.9) years, respectively. Compared with eGFRcr, eGFRBTP and eGFRB2M improved risk associations and modestly improved prediction for ESRD and death even after adjustment for established risk factors. eGFRavg provided the most consistent improvement in associations and prediction across both outcomes and populations. Assessment of heterogeneity did not yield clinically relevant differences. For ESRD, addition of albuminuria substantially attenuated the improvement in risk prediction and risk classification with novel filtration markers. For mortality, addition of albuminuria did not affect the improvement in risk prediction with the use of novel markers, but lessened improvement in risk classification, especially for the CKD cohort. CONCLUSIONS These markers do not provide substantial additional prognostic information to eGFRcr and albuminuria, but may be appropriate in circumstances where eGFRcr is not accurate or albuminuria is not available. Educational efforts to increase measurement of albuminuria in clinical practice may be more cost-effective than measurement of BTP and B2M for improving prognostic information.

Rare erroneous results on the Siemens Dimension Vista® platform due to urine carryover: A warning to current users

In 2014, the West Bank Laboratory at the University of Minnesota, part of the non-profit Fairview Health Services system, went live with two Siemens Dimension Vista® 500 instruments. In the first few months after go-live, the lab began receiving reports of rare, erroneous results from clinicians. After further investigation it was noted that most of the errors being reported followed a consistent pattern with significantly elevated potassium, BUN and creatinine. After months of unsuccessful troubleshooting with Siemens, our lab and others within the Fairview Health Services system began hypothesizing that urine carryover was occurring due to the pattern of elevated analytes, and asked Siemens to investigate this hypothesis. In March 2016 Siemens confirmed a software defect which omits an aliquot probe rinse resulting in sample carryover in rare cases. Our objective is to alert current users of the Siemens Dimension Vista® instruments to this rare but alarming phenomenon, discuss the frequency and impact of the erroneous results at our institution, and detail recommended steps for users of Siemens Dimension Vista® instruments to help retrospectively determine whether they have experienced similar erroneous results.

Critically Elevated Potassium in a 55-Year-Old Female With Chronic Lymphocytic Leukemia

Hyperkalemia in specimens from patients with chronic lymphocytic leukemia (CLL) may be due to tumor lysis syndrome (TLS) or specimen processing. This report describes a 55-year-old Caucasian woman with CLL who presented to an outside hospital with hyperkalemia and was transferred to a second hospital. Initial evaluation on the core laboratory chemistry analyzer (the VITROS 5600) and the ABL90 FLEX blood gas analyzer showed markedly elevated levels of potassium (K+). TLS was subsequently diagnosed, and dialysis was initiated. However, follow-up K+ measurements in whole blood (WB) yielded low levels that were unexpected after a single dialysis treatment. We then discovered that the initially elevated K+ level was from centrifuged plasma specimens and concluded that it indicated pseudohyperkalemia, likely from centrifugation. This case demonstrates that medical teams need be alert to potentially false K+ results in patients with elevated white blood cell counts. WB specimens are preferable, and steps to minimize trauma to the specimen and immediate analysis using blood gas instruments are recommended.

A 43-year-old woman with unexplained elevation of hCG

OBJECTIVE This case report investigates an unusual hCG result in a woman who is not pregnant. PATIENT AND METHODS A 43-year-old woman was admitted for recurrence of thrombotic thrombocytopenic purpura (TTP) and therapeutic plasma exchange (TPE) was initiated. Prior to transitioning the patient from TPE to immunosuppressive therapy, a serum qualitative hCG test was performed and was positive. Several etiologies for elevated hCG were considered and investigated, including heterophile antibody interference, endogenous hCG from pituitary or malignancy, and exogenous hCG. RESULTS Retrospective measurement of hCG levels in remnant samples, including a sample obtained prior to TPE initiation, demonstrated that the hCG elevation occurred with plasma administration for TPE. Further investigation with the American Red Cross confirmed that a plasma donor was unknowingly pregnant and in the latter half of the first trimester at the time of donation, when hCG levels peak. CONCLUSION In plasma recipients with unexplained hCG elevation, passive transfer of hCG from plasma should be considered in the differential diagnosis. Retrospective measurement of hCG in remnant samples obtained prior to plasma exchange can assist in confirming the source.

Determining the utility of creatinine delta checks: A large retrospective analysis

INTRODUCTION Delta checks are a long-standing practice for identifying errors in the laboratory. However, with the decrease in errors due to laboratory automation, their utility is unclear. The objective of this retrospective analysis was to determine whether establishment of a creatinine delta check would be an effective means for capturing true laboratory error. METHODS All patients with a minimum of two creatinine results during March of 2015 were selected for review (n = 23,410 creatinine results). The lowest % change for a previously confirmed creatinine error in our laboratory was approximately 60%; therefore only results that changed by at least ±60% (n = 254) were reviewed. The etiology of creatinine value change was categorized as laboratory error, pathologic change, or non-pathologic change, based upon chart review. RESULTS 1.2% (3/254) of reviewed delta checks were determined to reflect 2 instances of true laboratory error that went unrecognized by laboratory staff. 91.3% (232/254) of the delta checks were determined to reflect a pathologic or dialysis-related change in creatinine levels. The remaining 7.5% of delta checks (19/234) were deemed to be non-pathologic changes in creatinine. DISCUSSION This study identified two instances of laboratory error reflected by 3 delta checks (1.2%); the vast majority (91.3%) of creatinine results that changed by ±60% were pathologic or dialysis-related. Thus, establishment of a ±60% delta check for creatinine would overwhelmingly flag true biological change and would not be an efficient means for identifying rare laboratory errors. Clinical laboratories should perform similar retrospective analyses prior to enacting delta checks to determine whether they will effectively capture laboratory error.

A Setback to Universal Pediatric Lipid Screening and a Call for More Research

In 2011, a report published by the National Heart, Lung, and Blood Institute on pediatric cardiovascular health and risk reduction put forth a recommendation for universal lipid screening in children and adolescents between the ages of 9 and 11 (1). Although the American Academy of Pediatrics, the National Lipid Association, and the American Heart Association have supported this recommendation, there has been substantial debate questioning this approach. Fuel was added to the fire in this debate when in August of this year the US Preventive Services Task Force (USPSTF) issued a report on childhood dyslipidemia, concluding there is insufficient evidence either in support of or against universal lipid screening in children and adolescents (2). A recent article published in Science entitled “Cholesterol screening for kids …