General Chemistry Analysis Research Articles

First two-reagent vitamin D assay for general clinical chemistry

BackgroundVitamin D is a lipid-soluble molecule that plays key physiological roles in the metabolism of calcium, phosphate and magnesium. Recent studies show that deficiency in vitamin D is linked to cardiovascular diseases, autoimmune diseases and cancer. As a result, regular monitoring of 25-OH vitamin D (the main circulating form of vitamin D) is becoming essential. Current 25-OH vitamin D testing methodologies are cumbersome (too many reagents, long incubation times, phase separation) and are not compatible with general clinical chemistry platforms. Here, we report on a novel method to detect 25-OH vitamin D that is fast (results in 10 min or less), simple (two reagents) and compatible with virtually all general clinical chemistry analyzers. MethodsAn immunoturbidimetric assay for 25-OH vitamin D (the Diazyme EZ Vitamin D Assay) has been developed using nanoparticles and vitamin D-specific antibodies. The performance of the assay kit, which consists of two reagents and five calibrators, was tested on the Beckman AU680 analyzer (AU680). ResultsThe new assay was precise, sensitive (LOD = 7.2 nmol/L), linear (up to 390.1 nmol/L) and correlated strongly (R2 > 0.95) with major commercial 25-OH vitamin D assays. Additionally, the assay was found to be the fastest to date, with the first results obtained within 10 min. Throughput on the AU680 was estimated at over 300 tests per hour. ConclusionsThe newly developed 25-OH vitamin D assay is fast, precise and accurate. It can be run on most general chemistry analyzers. This assay aims at providing vitamin D-testing capabilities to all clinical chemistry laboratories.

Woman with Hypomagnesemia and Hypocalcemia

A 71-year-old woman was referred to the endocrinology clinic after several years of unresolved hypomagnesemia that required numerous hospital admissions to receive intravenous magnesium. She previously presented with palpitations on 3 occasions, and once with diarrhea and vomiting. The blood tests on all 4 presentations demonstrated severe hypomagnesemia (Table 1). View this table: Table 1. Laboratory results during previous visits.a Her medical history included type 2 diabetes mellitus and hiatal hernia. Her regular medications included simvastatin, esomeprazole, verapamil, pioglitazone, gliclazide, metformin, and calcium, magnesium, and vitamin D supplementation. Clinical examination in the endocrinology clinic was unremarkable, and no abnormality was demonstrated on electrocardiogram. An echocardiogram was normal. Laboratory results at this visit included serum magnesium 0.52 mg/dL (0.21 mmol/L) [reference interval 1.7–2.4 mg/dL (0.7–1.0 mmol/L)] and serum calcium 6.84 mg/dL (1.71 mmol/L) [reference interval 8.8–10.6 mg/dL (2.20–2.65 mmol/L)]. Serum albumin was 35 g/L (reference interval 35–52 g/L). The results of her other biochemical tests were unremarkable. Twenty-four-hour urine magnesium excretion was undetectable [reference interval 0.5–1.2 mg/dL (0.2–5.0 mmol/24 h)], as was random urine magnesium [<0.25 mg/dL (<0.1 mmol/L)]. Intact parathyroid hormone (PTH)3 was 20 ng/L (reference interval 15–88 ng/L), inappropriately low in the presence of hypocalcemia. All analytes were measured with a Beckman Olympus AU2700 general chemistry analyzer with the exception of intact PTH, which was measured with a Beckman Coulter Access II. The patient gave full written consent for the use of her clinical information and laboratory tests for the purposes of a case report in the medical literature. ### QUESTIONS TO CONSIDER 1. What are the common causes of hypomagnesemia? 2. Are any of the patient's medications potential causes of hypomagnesemia? 3. What effect does magnesium have on calcium and parathyroid hormone? The patient was advised to stop …

Direct enzymatic assay for %HbA1c in human whole blood samples

Objectives Development and validation of a direct enzymatic HbA1c assay that utilizes a single channel on chemistry auto-analyzers without the need to run separate glycated hemoglobin and total hemoglobin assays. Design and methods An enzyme based single channel assay was developed to measure %HbA1c in human whole blood samples. The performance characteristics of the Diazyme Direct Enzymatic HbA1c Assay were evaluated on the Hitachi 917 auto-analyzer using whole blood samples, appropriate controls and a reference lot of manufactured reagents. Accuracy studies were completed by comparing the Direct Enzymatic Assay to existing HPLC and immunoassay methods. Interference testing was performed to determine the effect of total hemoglobin, glycated serum proteins, chemical substances and hemoglobin variants in patient samples. Results The Direct Enzymatic HbA1c Assay showed within run precision and total precision results of ≤ 2% CV for both normal and abnormal level samples. Method comparison studies showed that there was a good correlation between the Direct Enzymatic HbA1c and the HPLC ( R 2 = 0.98) or the immunoassay ( R 2 = 0.97) methods. The assay measured within the range of 4–16% HbA1c and showed excellent performance with variant hemoglobin in samples. Conclusions Diazyme Direct Enzymatic HbA1c Assay is accurate and precise when compared to currently marketed medical devices. The assay is designed to report %HbA1c values directly without need for a separate measurement of total hemoglobin and is not adversely affected by interferences from common hemoglobin variants in samples. It is a cost effective, user-friendly method and is adaptable to most general chemistry analyzers.

Study of lipid profile from RIQAS quality control sample

The laboratory of the present author is a participant of Randox International Quality Assessment Scheme (RIQAS). The author receives twenty six samples for thirty nine general chemistry analysis per year, reports of which are to be sent fortnightly. Amongst thirty nine analytes there are partial lipid profile parameters like total cholesterol and triglycerides. So, the author decided to run a pilot study of full lipid profile from these samples. At the first phase four samples from two different cycles were considered as test materials. The reports of these samples were quite satisfactory. The trial run was given for fifteen consecutive days. (Presented by the author in the Annual Conference of ACBI, 2004).The success of trial runs for fifteen days proved that EQA samples from RIQAS may be used for full lipid profile analysis. Results were compared against Randox internal quality control samples (IQA) and were found to be accurate and reproducible.

Latex agglutination test for ferritin measurement.

Ferritin is an indispensable parameter in the diagnosis of latent iron deficiency anemia or siderosis. In this study, we evaluated the utility of a reagent for ferritin measurement in a latex agglutination (LA) test, using general chemistry analyzers. The intraassay coefficient of variation (CV) was 0.8-3.4% and the interassay CV was 0.0-0.7%. Linearity was observed up to 1100 ng/mL. The effective sensitivity value was 4.0 ng/mL. In addition, good results were obtained with the prozone test, the effects of interferences, correlation with the enzyme immunoassay (EIA) method, and functional assay sensitivity. A significant positive correlation with C-reactive protein (r=0.586, P<0.001) was found. When compared with liver-related biochemical parameters (asparate aminotransferase (AST) and alanine aminotransferase (ALT)) in patients with impaired liver function, ferritin varied in parallel with the liver-related parameters. This assay system was able to measure ferritin accurately over a wide range, and thus could be used to diagnose cancer, siderosis, and iron deficiency anemia. The LA assay system can be employed for measurement with general chemistry analyzers, with rapid and convenient execution. In addition, the LA test allows the simultaneous measurement of other markers of iron deficiency anemia, so clinicians can rapidly obtain examination results.

Evaluation of a Particle-enhanced Turbidimetric Immunoassay for the Measurement of Immunoglobulin E in an ILab 900 Analyzer

The measurement of immunoglobulin E (IgE) in serum is widely used in the diagnosis of allergic reactions and parasitic infections. We describe here a fully automated assay for human IgE suitable for routine application in a general chemistry analyzer. We used an ILab 900 analyzer. This instrument automates a particle-enhanced immunoturbidimetric assay with an analysis time of 9 min. The assay was linear in the range 4-1000 kIU/L (r = 0.9998). The intra- and interassay CVs at 57, 235, and 434 kIU/L were <3.5% and <7.4%, respectively. The detection limit was 4 kIU/L. Hemoglobin (</=16 g/L), bilirubin (</=250 micromol/L), and myeloma paraproteins did not interfere with the assay. The assay showed good correlation with a microparticle enzyme immunoassay (r = 0.998) with a mean difference between methods of -6 +/- 26 kIU/L. The new automated serum assay for IgE is an attractive alternative that avoids the need for dedicated instrumentation.

Methodology and Subspecialty Consolidation in the Clinical Laboratory

The design of instruments as automated workstations for the clinical laboratory has evolved steadily over the last two decades. The grouping of assays into clinical chemistry disciplines has been largely influenced by the instrumentation available, e.g., multicomponent chemistry analyzers and specialty analyzers, including analyte-specific analyzers, blood gas analyzers, nephelometers, instruments dedicated to therapeutic drug monitoring (TDM), and instruments dedicated to protein or other immunoassays. This evolution has been a synergy of needs and technologies. The advent of managed care has led to stringent efforts to decrease the unit costs of laboratory testing and to increase productivity. Increases in efficiency in the clinical laboratory can be achieved by modifying the overall process flow and by using more-efficient technologies. These changes are assumed to decrease labor requirements and, therefore, to decrease the major component of the direct cost of testing. The use of multiple instrument types, however, even for such altruistic reasons as optimizing analytical performance, can create a process and scheduling problem in attempts to reduce unit costs (1)(2). Each instrument utilized in a clinical chemistry laboratory (or in a multidiscipline automated core laboratory) incurs support costs: for calibration, regulation compliance, utilities, maintenance (including service contracts), computer interfacing, and inventory control, among others. These costs will exist if the front and back ends of the specimen-processing functions are completely automated. Therefore, even if all specimen manipulations are automated, reducing the number of instrument workstations can still reduce costs. The report by Scholer et al. in this issue of Clinical Chemistry describes an immunoturbidimetric method for digoxin that requires no pretreatment (3). The assay is adaptable to general chemistry analyzers, and its performance at several different centers with a variety of instrumentation is well documented here (3). Considering the analytical requirements for an acceptable assay for serum digoxin, the performance …

Application of existing technology to meet increasing demands for automated sample handling

As the clinical laboratory advances toward total automation, the marketplace is now demanding more-efficient sample-handling systems. These demands have arisen over a relatively short period of time, in part because of heightened concern over laboratory safety and the resulting manpower shortages. Adding sample-handling capabilities to existing instrumentation is often a challenge, because usually mechanical or system constraints are present that interfere. This challenge has been overcome in the DuPont Sample Management System (SMS), a second-generation general chemistry analyzer that incorporates the latest barcode and computer-interfacing technology. The development of the SMS system relies heavily on recent advances in technology, e.g., software modeling and computer-aided design. The SMS system includes a barcode scanner based on "charge-coupled device" technology, a random-access sample wheel, and new software that oversees the various functions.