Urine Albumin Measurements in Clinical Diagnostics.

BACKGROUND: Measurement of urine albumin is critical for diagnosis, risk classification, and monitoring of chronic kidney disease (CKD). Guidelines recommend clinical decision cutoffs for the urine albumin-to-creatinine ratio (ACR) of 30 and 300 mg/g (3 and 30 mg/mmol). However, differences among manufacturers' routine urine albumin measurement procedures have been found to exceed 40%, suggesting CKD diagnosis and risk classification may vary depending upon the specific measurement procedure implemented in the laboratory. CONTENT: This review discusses urine albumin pathophysiology and clinical practice guideline recommendations for CKD. The review also provides recommendations for urine specimen collection and storage, and results reporting for the ACR. Recent advances in measurement techniques and development of reference systems intended to facilitate standardization of urine albumin measurements are reviewed. SUMMARY: Urine albumin is an important measurement procedure used for diagnosis, risk classification, and management of CKD. Urine albumin results should be reported as the ACR using quantitative measurement procedures. Random urine collections used for albuminuria screening should be followed by confirmation with first morning void collections to reduce variation and increase diagnostic accuracy for urine albumin measurement. Most measurement procedures utilize immunoturbidimetric or immunonephelometric techniques. However, results vary significantly among measurement procedures, potentially resulting in differences in classification or risk assessment for CKD. The National Institute for Standards and Technology (NIST) and other laboratories are developing reference systems, including liquid chromatography-tandem mass spectrometry candidate reference measurement procedures and reference materials, to enable standardization of routine measurement procedures.

Evaluation of Strontium Interference in Calcium Measurement Procedures and Content in Supplements as Measured by ICP-MS.

BACKGROUND: Bone health supplements containing strontium are available without prescription, however, the effects of strontium interference on clinical laboratory calcium measurement procedures are unknown. METHODS: To evaluate strontium interference on total calcium measurements, plasma pools with exogenously added strontium were measured by 3 total calcium measurement procedures. For ionized calcium measurements, whole blood pools prepared with exogenously added strontium were measured by 2 ionized calcium measurement procedures. An inductively coupled plasma mass spectrometry assay (ICP-MS) was validated for research measurements of strontium content in commercially available supplements. RESULTS: Exogenous strontium addition to plasma caused positive bias for total calcium measurements. Strontium concentrations of 1.0 mg/dL (0.114 mmol/L), 2.5 mg/dL (0.284 mmol/L), and 5.0 mg/Dl (0.568 mmol/L) resulted in mean biases of 1.9% to 3.5%, 4.9% to 9.0%, and 10.8% to 19.2%, respectively, for total calcium measurement procedures. Biases for ionized calcium measurements were less than 4.5% for a strontium concentration of 5.0 mg/dL (0.568 mmol/L). An in-house-developed ICP-MS assay for strontium in commercially available supplements exhibited within-laboratory and within-run coefficients of variation of less than 3%, and a linear response was obtained over the assay analytical measurement range of 10 to 100 000 ng/mL (0.0001 to 1.141 mmol/L). Strontium recovery for the ICP-MS assay was 97.1% to 105.3%. The largest amount of strontium measured in dietary supplements was 395 mg in a 1054 mg tablet. CONCLUSIONS: Some dietary supplements contain larger amounts of strontium than indicated on the product label. High concentrations of strontium may cause significant interference for total calcium measurement procedures, but ionized calcium measurement procedures are not significantly affected.

Cross-Institutional Evaluation of the Abbott ARCHITECT SARS-CoV-2 IgG Immunoassay.

OBJECTIVE: To describe a cross-institutional approach to verify the Abbott ARCHITECT SARS-CoV-2 antibody assay and to document the kinetics of the serological response. METHODS: We conducted analytical performance evaluation studies using the Abbott ARCHITECT SARS-CoV-2 antibody assay on 5 Abbott ARCHITECT i2000 automated analyzers at 2 academic medical centers. RESULTS: Within-run and between-run coefficients of variance (CVs) for the antibody assay did not exceed 5.6% and 8.6%, respectively, for each institution. Quantitative and qualitative results agreed for lithium heparin plasma, EDTA-plasma and serum specimen types. Results for all SARS-CoV-2 IgG-positive and -negative specimens were concordant among analyzers except for 1 specimen at 1 institution. Qualitative and quantitative agreement was observed for specimens exchanged between institutions. All patients had detectable antibodies by day 10 from symptom onset and maintained seropositivity throughout specimen procurement. CONCLUSIONS: The analytical performance characteristics of the Abbott ARCHITECT SARS-CoV-2 antibody assay within and between 2 academic medical center clinical laboratories were acceptable for widespread clinical-laboratory use.

Detecting direct oral anticoagulants in trauma patients using liquid chromatography-mass spectrometry: A novel approach to medication reconciliation.

BACKGROUND: Accurate medication reconciliation in trauma patients is essential but difficult. Currently, there is no established clinical method of detecting direct oral anticoagulants (DOACs) in trauma patients. We hypothesized that a liquid chromatography-mass spectrometry (LCMS)-based assay can be used to accurately detect DOACs in trauma patients upon hospital arrival. METHODS: Plasma samples were collected from 356 patients who provided informed consent including 10 healthy controls, 19 known positive or negative controls, and 327 trauma patients older than 65 years who were evaluated at our large, urban level 1 trauma center. The assay methodology was developed in healthy and known controls to detect apixaban, rivaroxaban, and dabigatran using LCMS and then applied to 327 samples from trauma patients. Standard medication reconciliation processes in the electronic medical record documenting DOAC usage were compared with LCMS results to determine overall accuracy, sensitivity, specificity, and positive and negative predictive values (PPV, NPV) of the assay. RESULTS: Of 356 patients, 39 (10.96%) were on DOACs: 21 were on apixaban, 14 on rivaroxaban, and 4 on dabigatran. The overall accuracy of the assay for detecting any DOAC was 98.60%, with a sensitivity of 94.87% and specificity of 99.05% (PPV, 92.50%; NPV, 99.37%). The assay detected apixaban with a sensitivity of 90.48% and specificity of 99.10% (PPV, 86.36%; NPV 99.40%). There were three false-positive results and two false-negative LCMS results for apixaban. Dabigatran and rivaroxaban were detected with 100% sensitivity and specificity. CONCLUSION: This LCMS-based assay was highly accurate in detecting DOACs in trauma patients. Further studies need to confirm the clinical efficacy of this LCMS assay and its value for medication reconciliation in trauma patients. LEVEL OF EVIDENCE: Diagnostic Test, level III.

Metabolomics and Precision Medicine in Trauma: The State of the Field.

Trauma is a major problem in the United States. Mortality from trauma is the number one cause of death under the age of 45 in the United States and is the third leading cause of death for all age groups. There are approximately 200,000 deaths per year due to trauma in the United States at a cost of over $671 billion in combined healthcare costs and lost productivity. Unsurprisingly, trauma accounts for approximately 30% of all life-years lost in the United States. Due to immense development of trauma systems, a large majority of trauma patients survive the injury, but then go on to die from complications arising from the injury. These complications are marked by early and significant metabolic changes accompanied by inflammatory responses that lead to progressive organ failure and, ultimately, death. Early resuscitative and surgical interventions followed by close monitoring to identify and rescue treatment failures are key to successful outcomes. Currently, the adequacy of resuscitation is measured using vital signs, noninvasive methods such as bedside echocardiography or stroke volume variation, and other laboratory endpoints of resuscitation, such as lactate and base deficit. However, these methods may be too crude to understand cellular and subcellular changes that may be occurring in trauma patients. Better diagnostic and therapeutic markers are needed to assess the adequacy of interventions and monitor responses at a cellular and subcellular level and inform clinical decision-making before complications are clinically apparent. The developing field of metabolomics holds great promise in the identification and application of biochemical markers toward the clinical decision-making process.

Baseline Assessment of 25-Hydroxyvitamin D Assay Performance: A Vitamin D Standardization Program (VDSP) Interlaboratory Comparison Study.

The Vitamin D Standardization Program (VDSP) coordinated an interlaboratory study to assess the comparability of measurements of total 25-hydroxyvitamin D [25(OH)D] in human serum, which is the primary marker of vitamin D status. A set of 50 individual donor samples were analyzed by 15 different laboratories representing national nutrition surveys, assay manufacturers, and clinical and/or research laboratories to provide results for total 25(OH)D using both immunoassays (IAs) and LC tandem MS (MS/MS). The results were evaluated relative to bias compared with the target values assigned based on a combination of measurements at Ghent University (Belgium) and the U.S. National Institute of Standards and Technology using reference measurement procedures for the determination of 25(OH)D2 and 25(OH)D3. CV and mean bias for each laboratory and assay platform were assessed and compared with previously established VDSP performance criteria, namely CV ≤ 10% and mean bias ≤ 5%. Nearly all LC-MS/MS results achieved VDSP criteria, whereas only 50% of IAs met the criterion for a ≤10% CV and only three of eight IAs achieved the ≤5% bias. These results establish a benchmark for the evaluation of 25(OH)D assay performance and standardization activities in the future.

Baseline Assessment of 25-Hydroxyvitamin D Reference Material and Proficiency Testing/External Quality Assurance Material Commutability: A Vitamin D Standardization Program Study.

The Vitamin D Standardization Program (VDSP) coordinated a study in 2012 to assess the commutability of reference materials and proficiency testing/external quality assurance materials for total 25-hydroxyvitamin D [25(OH)D] in human serum, the primary indicator of vitamin D status. A set of 50 single-donor serum samples as well as 17 reference and proficiency testing/external quality assessment materials were analyzed by participating laboratories that used either immunoassay or LC-MS methods for total 25(OH)D. The commutability test materials included National Institute of Standards and Technology Standard Reference Material 972a Vitamin D Metabolites in Human Serum as well as materials from the College of American Pathologists and the Vitamin D External Quality Assessment Scheme. Study protocols and data analysis procedures were in accordance with Clinical and Laboratory Standards Institute guidelines. The majority of the test materials were found to be commutable with the methods used in this commutability study. These results provide guidance for laboratories needing to choose appropriate reference materials and select proficiency or external quality assessment programs and will serve as a foundation for additional VDSP studies.

Method for Continuous Monitoring of Electrospray Ion Formation.

A method for continuously monitoring the performance of electrospray ionization without the addition of hardware or chemistry to the system is demonstrated. In the method, which we refer to as SprayDx, cluster ions with solvent vapor natively formed by electrospray are followed throughout the collection of liquid chromatography-selected reaction monitoring data. The cluster ion extracted ion chromatograms report on the consistency of the ion formation and detection system. The data collected by the SprayDx method resemble the data collected for postcolumn infusion of analyte. The response of the cluster ions monitored reports on changes in the physical parameters of the ion source such as voltage and gas flow. SprayDx is also observed to report on ion suppression in a fashion very similar to a postcolumn infusion of analyte. We anticipate the method finding utility as a continuous readout on the performance of electrospray and other atmospheric pressure ionization processes. Graphical Abstract ᅟ.

State of Harmonization of 24 Serum Albumin Measurement Procedures and Implications for Medical Decisions.

BACKGROUND: Measurements of serum and plasma albumin are widely used in medicine, including as indicators of quality of patient care in renal dialysis centers. METHODS: Pools were prepared from residual patient serum (n = 50) and heparin plasma (n = 48) from patients without renal disease, and serum from patients with kidney failure before hemodialysis (n = 53). Albumin was measured in all samples and in ERM-DA470k/IFCC reference material (RM) by 3 immunochemical, 9 bromcresol green (BCG), and 12 bromcresol purple (BCP) methods. RESULTS: Two of 3 immunochemical procedures, 5 of 9 BCG, and 10 of 12 BCP methods recovered the RM value within its uncertainty. One immunochemical and 3 BCG methods were biased vs the RM value. Random error components were small for all measurement procedures. The Tina-quant immunochemical method was chosen as the reference measurement procedure based on recovery and results of error analyses. Mean biases for BCG vs Tina-quant were 1.5% to 13.9% and were larger at lower albumin concentrations. BCP methods' mean biases were -5.4% to 1.2% irrespective of albumin concentration. Biases for plasma samples were generally higher than for serum samples for all method types. For most measurement procedures, biases were lower for serum from patients on hemodialysis vs patients without kidney disease. CONCLUSIONS: Significant differences among immunochemical, BCG, and BCP methods compromise interpretation of serum albumin results. Guidelines and calculations for clinical management of kidney and other diseases must consider the method used for albumin measurement until harmonization can be achieved.

Standardization of Urine Albumin Measurements: Status and Performance Goals.

BACKGROUND: Urine albumin is a key laboratory test used for classification, assessment of risk, and monitoring treatment of patients with chronic kidney disease. Urine albumin measurement results are not standardized among different measurement procedures. Consequently, clinical guidelines using fixed decision values for urine albumin cannot be applied consistently. CONTENT: Isotope dilution mass spectrometry reference measurement procedures and certified reference materials are being developed to enable standardization of immunoassay measurement procedures for urine albumin. A previous report determined calibration bias was the major error source for differences in results among different measurement procedures for urine albumin. Performance goals for between-day precision, ≤6% CV above 15 mg/L, and for specimen-specific effects, ≤6% CV, were established on the basis of the performance capability of current measurement procedures. The biological variation model was used to estimate a total allowable error of ≤24%-30% and from that the goal for bias of ≤7%-13%. SUMMARY: A reference system of higher-order certified reference materials and reference measurement procedures is being developed to enable standardization of urine albumin measurement results. Goals have been established for total allowable error, specimen-specific effects, imprecision, and bias to facilitate efforts to standardize urine albumin measurement results.

Moving Toward Standardization of Urine Albumin Measurements.

Measurement of urine albumin is important for detecting and monitoring kidney disease. At the present time, measurement of urine albumin is not standardized due to the lack of a reference system, which includes both a reference measurement procedure and certified reference materials. Developing a reference system will provide a means for clinical laboratory measurement procedures to become standardized and will enable successful use of uniform clinical decision points. Currently, urine albumin results vary in excess of 40% depending on which commercially available measurement procedure is utilized for measurement. Clinicians may struggle with classification of kidney disease in part due to differences in measurements from lack of agreement among laboratory methodologies employed when assessing urine albumin concentrations. This report focuses on current findings in urine albumin testing, highlights important measurement and reporting considerations, and presents strategies for developing a reference measurement procedure to enable standardization of urine albumin measurements.

Difference in bias approach for commutability assessment: application to frozen pools of human serum measured by 8 direct methods for HDL and LDL cholesterol.

BACKGROUND: We used a difference in bias approach to evaluate the commutability of 4 frozen serum pools for 8 direct methods for measurement of HDL and LDL cholesterol (HDLC and LDLC). METHODS: Freshly collected nonfrozen sera from 138 diseased and 37 nondiseased patients and 4 frozen pools from the CDC Lipid Standardization Program were measured by direct methods and by the beta-quantification reference measurement procedure of the CDC. We used an error components model to estimate the difference in the bias component of error plus its uncertainty for frozen pools vs patient samples between the direct method and the reference procedure. Frozen pools with bias differences less than a critical value determined by either medical requirements for bias or the random error components of the measurement procedures were considered commutable. RESULTS: On the basis of medical requirement criteria, 1 of the 4 frozen pools was commutable for most of the HDLC methods for both diseased and nondiseased patients, and none was commutable for LDLC methods. On the basis of random error criteria, all of the frozen pools were generally commutable for all of the HDLC methods for both diseased and nondiseased patients, and 1 of the 4 frozen pools was generally commutable for most of the LDLC methods for both diseased and nondiseased patients. CONCLUSIONS: Commutability was assessed as the closeness of agreement of the difference in bias between a reference material and a set of patient samples. Criteria for commutability could be based on fixed medical requirements for bias or on random error components.