Requirements for improving quality in the measurement of bone markers

BACKGROUND

A number of biochemical assays readily detect molecules released from the bone matrix and collagen degradation in both serum and urine specimens. The variability of bone biochemical markers is still an issue of practical concern limiting their wider clinical use, and compromising the management of the individual patient. The aim of the present study was to define quality specifications of bone markers measurement in the total testing process.

METHODS

The different sources of biological variability of biochemical bone marker were assessed according to the current knowledge and categorized as pre-analytical, intra-analytical and post-analytical.

RESULTS

The identification of factors influencing bone marker measurements allowed recommendations to be made for decreasing pre- and intra-analytical variation in order to improve laboratory performance. The assessment of post-analytical sources of variation, moreover, involves the practical use of bone markers in identifying individual women at risk of fractures and the identification of non-responders, providing adequate limit value, least significant change value or optimal threshold of bone marker change.

CONCLUSIONS

Laboratory services may improve the potential clinical applications of biochemical markers of bone remodeling by improving method standardization, defining and reducing pre-analytical and analytical variables and providing reports that specify analytical and biological variation or cut-off values, thus facilitating data interpretation or reports.

Assessment of iodine intake in mildly iodine-deficient pregnant women by a new automated kinetic urinary iodine determination method

Maternal iodine deficiency can compromise the thyroid status of the mother, fetus and newborn child. Therefore, it is important to assess the iodine excretion level of groups of pregnant women. In this study we aimed to determine iodine intake in pregnancy using a recently reported automated kinetic method for urinary iodine determination. Urinary iodine measurements of 123 pregnant women (18 first, 28 second and 77 third trimester) were carried out using a new automated kinetic assay based on the Sandell-Kolthoff reaction at 37°C and its kinetic measurement at 340nm in a random-access automated analyzer after ammonium persulfate digestion at 95°C in a water bath with ±0.1°C precision. Statistical analyses were carried out using SPSS software. Whole group, first trimester, second trimester and third trimester urinary iodine concentrations (mean±SD) in pregnant women were 1.13±0.81, 1.08±0.71, 0.86±0.58 and 1.27±0.87μmol/L, respectively. The urinary iodine concentration significantly increased with gestational age (p<0.05). We found that our study group was mildly iodine-deficient according to WHO criteria. Furthermore, the pregnant women were found to be mildly iodine-deficient in the first and third trimesters and moderately so in the second trimester. The only statistical difference was between second and third trimester values (p<0.05). Even though the increased iodine deficiency in the second trimester is not useful for early detection of iodine deficiency in pregnancy, the severity of this deficiency in the second trimester may lead to important effects on thyroid metabolism for both mother and fetus. Our study suggests that the iodine excretion of pregnant women living in iodine-deficient areas could be assessed using this fast and automated method.

Easy fix for clinical laboratories for the false-positive defect with the Abbott AxSym total beta-hCG test

BACKGROUND

False-positive hCG results can lead to erroneous diagnoses and needless chemotherapy and surgery. In the last 2 years, eight publications described cases involving false-positive hCG tests; all eight involved the AxSym test. We investigated the source of this abundance of cases and a simple fix that may be used by clinical laboratories.

METHODS

False-positive hCG was primarily identified by absence of hCG in urine and varying or negative hCG results in alternative tests. Seventeen false-positive serum samples in the AxSym test were evaluated undiluted and at twofold dilution with diluent containing excess goat serum or immunoglobulin.

RESULTS

We identified 58 patients with false-positive hCG, 47 of 58 due to the Abbott AxSym total hCGbeta test (81%). Sixteen of 17 of these "false-positive" results (mean 100 mIU/ml) became undetectable when tested again after twofold dilution.

CONCLUSIONS

A simple twofold dilution with this diluent containing excess goat serum or immunoglobulin completely protected 16 of 17 samples from patients having false-positive results. It is recommended that laboratories using this test use twofold dilution as a minimum to prevent false-positive results.

Effect of blood collection tubes on total triiodothyronine and other laboratory assays

BACKGROUND

Increased total triiodothyronine (TT(3)) assay results in apparently euthyroid patients triggered an investigation of the effect of blood collection tubes on serum TT(3) and other laboratory assays.

METHODS

We examined potential assay interference for three types of tubes: plastic Greiner Bio-One Vacuette; glass Becton Dickinson (BD) Vacutainer; and plastic BD Vacutainer SST tubes. Serum samples from apparently healthy volunteers (age range, 30-60 years; 15 males and 34 females) were collected in different tube types and analyzed in 17 immunoassays (n = 49), 30 clinical chemistry tests (n = 20), and 33 immunology assays (n = 15). Tube effects were also examined by adding pooled serum to different tube types.

RESULTS

TT(3) values, when measured by the IMMULITE 2000 but not the AxSYM analyzer, were significantly higher (P <0.0001) for SST (2.81 nmol/L) than either glass (2.15 nmol/L) or Vacuette (2.24 nmol/L) tubes. The effect was large enough to substantially shift the distribution of patient values, increasing the percentage of values above the reference interval from 11.3% to 35.8%. The degree of interference from SST tubes on TT(3) differed among various tube lots and could be attributed to a tube additive shared by other plastic tubes. Results from several other tests statistically differed among tube types, but differences were not considered to be clinically significant.

CONCLUSIONS

Assay interferences from blood collection tubes represent challenges to clinical laboratories because they are not detected by the usual quality-control or proficiency testing programs. Laboratories can, however, address this problem by monitoring distribution of patients' results.

[Urinary iodide analysis: critical study of the digestion method]

Urinary iodine is largely measured in microtiter plates by a colorimetic ceric-arsenic assay based on the Sandell-Kolthoff reaction. However, a preliminary digestion step is necessary and requires a particular care not only to transform all the iodo-compounds into iodide but also to prevent the formation of substances liable to the disturb of the subsequent redox reaction. In the present study we tested three types of digestion processes, among them two conventional methods (ammonium persulfate and chloric acid) and a new one using combined nitric acid/hydrochloric acid. Results showed that important errors may be obtained with the chloric acid and the ammonium persulfate digestions. These discordances were the consequence of either an incomplete transformation of iodo-compounds or an oxidation of iodide into molecular iodine or a colorimetric assay disturbance due to a residual yellow coloring. No problems were evidenced with the combined nitric acid/hydrochloric acid process, which remains the better alternative to evaluate the urinary iodine. It could also provide a particularly useful means of assessing the iodine status in epidemiological studies.

Evaluation of a new generation of plastic evacuated blood-collection tubes in clinical chemistry, therapeutic drug monitoring, hormone and trace metal analysis

Polyethylene terephthalate (PET) tubes have several advantages over glass tubes: they are unbreakable, lighter and more easily disposed of. Despite a steady increase in their use and an expansion of the range of available tubes, few studies validating their use have been published in the literature. This paper describes the various studies that have been performed to compare VENOJECT glass, VENOSAFE PET and VENOSAFE PET/heparin tubes for the assay of a panel of analytes in routine clinical chemistry, immunochemistry, hormone and tumor marker analysis and trace metal determination. These studies demonstrate that VENOSAFE PET tubes are a suitable alternative to glass tubes.

Objective determination of appropriate reporting intervals

BACKGROUND

The reporting interval is the incremental value chosen in reporting analyte concentration. Reporting intervals for different analytes are often inappropriately narrow, when analytical imprecision and biological variability are considered.

METHODS

We have used statistical techniques to determine intervals for individual analytes at which there is 50% or 95% confidence that two results are analytically different, and compared these with the reporting intervals in use for a range of general chemistry analytes and analytes usually measured by immunoassay.

RESULTS

No analytes met the criteria for 95% confidence that the results are analytically different. Even at the 50% confidence level, 24 of 46 analytes failed at all concentrations examined. For some analytes, particularly hormones at high concentration, the reporting interval increment should be increased by a factor of at least ten.

CONCLUSIONS

The majority of analytes are inappropriately reported when analytical precision alone is considered. The concept of the 'uncertainty of measurement' has not been adequately addressed. A consensus should be reached and implemented on appropriate reporting intervals for all analytes.

[Comparison of three methods for quantitative analysis of LPO in different biological samples]

OBJECTIVE

To explore the optimized methods for detecting lipid peroxide (LPO) in biological samples and the reference value of LPO in human plasma.

METHODS

Three most commonly adopted methods were used for detecting LPO in different biological samples simultaneously, and then their linearity, accuracy, precision, stability and detecting efficiency were compared. The methods were FOX assay, Modified iodometric assay and TBARS assay. The standard curve (linearity evaluation), rate of sample recovery (accuracy evaluation), reproducibility (precision evaluation), stability of reading number (stability evaluation), as well as the detected values of LPO in different sample systems by three methods simultaneously (detecting efficiency) were evaluated. The sample systems were: isolated low-density lipoprotein (LDL), supernatant of cell culture, and human plasma.

RESULTS

When applied to detecting LPO in the isolated LDL sample system, FOX assay was found to have the most sensitive detecting efficiency, good accuracy and precision. When applied to detecting LPO in the supernatant of cell culture and human plasma sample systems, the Modified iodometric assay and TBARS assay showed better function than FOX assay; the rate of sample recovery of FOX assay 61.92% +/- 2.92% was obviously lower as compared with 99.00% +/- 2.65% of modified iodometric assay and 101.63% +/- 12.00% of TBARS assay; and the reproducibility of FOX assay 19.15% was also lower as compared with 4.36% of Modified iodometric assay and 3.14% of TBARS assay. The three methods all showed fine linearity and stability. The values of LPO concentration in normal human plasma were (14.189 +/- 4.889) mumol/L by Modified iodometric assay and (0.936 +/- 0.462) mumol/L by TBARS assay; these values were close to those in other reports.

CONCLUSION

FOX assay was found to be most sensitive in the three methods for measurement of LPO in a relative pure sample system (such as isolated LDL). In complex sample system, however, the Modified iodometric assay and TBARS assay showed better function. The authors suggest that suitable method be chosen according to the nature of sample, that more than one method be chosen for plasma LPO assay in the same planned analysis, and that Modified iodometric assay and TBARS assay be worth the first choice.

[Countermeasures against non-specific reactions in the measurement of beta-glucan in plasma by alkaline treatment, chromogenic automated kinetic assay]

We investigated the detection of non-specific reactions in the measurement of plasma (1-->3)-beta-D-glucan (beta-glucan) and countermeasures against them using alkaline treatment, chromogenic automated kinetic assay (alkaline-kinetic assay). In this study, we reexamined the values of beta-glucan using the alkaline-kinetic assay with and without laminaran oligosaccharides (LO) as a kind of beta-glucan that blocks the Limulus reaction. The materials for this study were 584 plasma samples in which beta-glucan had been measured. These were taken from 232 patients in Kawasaki Medical School Hospital between January 2002 and March 2002. Non-specific reactions were judged by a calculated value under a LO additive condition. Determination as to whether or not the each time course of the Limulus reaction was influenced by a non-specific reaction was also studied by applying a non-specific reaction index set up independently. Non-specific reactions were recognized in 51.9% of the samples (81/156). The amount of non-specific reaction was 9.9 pg/ml or less in major samples. On the other hand, when the cut off value of the index for detection of non-specific reactions was set at 0.5, the sensitivity was 88.9% and specificity was 73.7%. The positive and negative predictive values were 93.5% and 60.9% respectively. Non-specific reactions can be approximately distinguished by applying the non-specific reaction index. By so doing, unnecessary initiation of anti fugal therapy in response to non-specific reactions can be avoided. Further prospective and radical studies of non-specific reactions in the alkaline-kinetic assay are necessary.

Sodium removal and sodium concentration during peritoneal dialysis: effects of three methods of sodium measurement

BACKGROUND

Sodium removal (NaR) may have a major impact on the survival of peritoneal dialysis patients. The dialysate/plasma sodium concentration ratio (D/P(Na)) is an indirect index of transcellular water transport by aquaporin channels, and thus of ultrafiltration. Sodium concentration can be assessed by means of flame photometry (F), and direct (D-ISE) or indirect ion-selective electrodes (I-ISE), but these methods have different properties. I-ISE is being used increasingly in clinical laboratories. The aim of this study was to evaluate NaR and D/P(Na) using the three different measurement methods.

METHODS

We performed peritoneal equilibration tests (PETs) in 44 peritoneal dialysis patients and calculated the NaR. We also calculated D/P(Na) during the test; plasma and dialysate sodium concentrations were measured by F, D-ISE and I-ISE.

RESULTS

NaR was lower (P<0.001) with D-ISE (69+/-29 mmol) than with F (81+/-29 mmol) or I-ISE (79+/-28 mmol). D/P(Na) was also lower at baseline (0.92+/-0.02 vs 0.95+/-0.02 and 0.95+/-0.02; P<0.001), after 60 min (0.87+/-0.03 vs 0.90+/-0.03 and 0.90+/-0.03; P<0.001) and at the end of PET (0.88+/-0.04 vs 0.92+/-0.04 and 0.92+/-0.04; P<0.001) when measured by D-ISE in comparison with F and I-ISE, respectively.

CONCLUSIONS

NaR and D/P(Na) were lower when measured by the D-ISE method compared with the F and I-ISE methods. NaR and D/P(Na) were similar when measured by F or I-ISE. I-ISE can be used reliably in the evaluation of NaR and D/P(Na) in everyday clinical practice of peritoneal dialysis.

Non-invasive diagnosis of Helicobacter pylori infection: simplified 13C-urea breath test, stool antigen testing, or DNA PCR in human feces in a clinical laboratory setting?

OBJECTIVES

(1) To compare two stool antigen EIAs (HpSA, FemtoLab) and PCR of ureaseA and cagA in feces, with (13)C-urea breath test (UBT). (2) To ascertain whether a simplified UBT (breath collection time = 10 min) is as reliable as the standard assay (30 min).

DESIGN AND METHODS

Helicobacter pylori status was recorded in Group 1 (n = 187) by UBT, H. pylori stool antigen, ureA and cagA PCR in feces. UBT with 10, 20 and 30 min sampling was performed in Group 2 patients (n = 283).

RESULTS

The sensitivity and specificity of HpSA, FemtoLab, and ureA were 67% and 99%, 90% and 96%, 35% and 98%, respectively. cagA results were positive in 16/48 H. pylori-positive, and in 5/100 H. pylori-negative patients. The results of UBT with a 10- and 30-min sampling strictly overlapped.

CONCLUSION

UBT with 10 min breath collection and FemtoLab stool antigen assay are the most reliable non-invasive tests to diagnose H. pylori infection.

Tenofovir-Related Nephrotoxicity: Case Report and Review of the Literature

Tenofovir is a nucleotide reverse transcriptase inhibitor for treatment of human immunodeficiency virus (HIV) infection. Several cases of renal failure associated with tenofovir therapy recently have been reported. A 54-year-old man with HIV experienced decreasing renal function and Fanconi's syndrome secondary to tenofovir therapy. His condition gradually improved after discontinuation of the drug. The available medical literature for reported cases of tenofovir-related nephrotoxicity indicates that this complication is apparently rare. However, our case report and literature review underscore the importance of monitoring renal function when treating patients with any nucleotide reverse transcriptase inhibitor.

Amphetamines and 3,4-methylendioxymetamphetamine (MDMA): evaluation of KIMS (kinetic interaction of microparticles in solution) assay at two cut-off levels

Two screening methods for the assay of amphetamines and their derivatives have been applied to the same analytical instrument for their evaluation. In addition to an assay at a cut-off of 1000 μg/l, a new specific reagent was evaluated for an ultra-sensitive assay of amphetamines and 3,4-methylendioxyme-tamphetamine with a cut-off of 300 μg/l. The assay confirmation was performed using high-performance liquid chromatography and gas chromatography/mass spectrometry techniques. The results were positive for both screening methods, confirming the efficacy of two simultaneous methods with different cut-off levels.

Near-patient testing for infection using urinalysis and immuno-chromatography strips

Urinary tract infections require costly confirmatory tests such as a urine culture to establish the diagnosis. Elimination of the culture step would save resources; diagnosis and treatment could begin in hours rather than days. We tested a new dip-and-read strip that uses immuno-chromatography (IC) to detect infectious agents in urine. We used a goat-derived polyclonal antibody with reactivity to the cell-wall proteins of

Proposal for guidelines to establish common biological reference intervals in large geographical areas for biochemical quantities measured frequently in serum and plasma

A suggestion for a standard procedure to establish biological reference intervals for biochemical quantities by a multicenter approach is presented. This procedure was developed for and used in the Nordic Reference Interval Project 2000 (NORIP). This project established biological reference intervals for 25 frequently requested biochemical quantities through cooperation of 102 Nordic laboratories. Each laboratory performed collection of reference samples and measurement using their routine methods. The bias of each routine method was eliminated by use of common reference materials measured in each of the participating laboratories.

Creation of the necessary analytical quality for generating and using reference intervals

This is a brief compilation of criteria on analytical quality that are prerequisites for the establishment and use of reference intervals in laboratory medicine. In this context, analytical quality is characterized by the precision, accuracy and long-term stability of laboratory methods performed with diagnostic kits, including their application on various instrument platforms. Systematically, analytical quality can be differentiated into quality of the method and its performance, and quality of long-term use. Factors influencing these types of quality in the development of diagnostic kits are discussed. The responsibility for maintaining analytical quality is shared by the two parties involved in the provision and use of reference intervals: The manufacturers of diagnostic kits are committed to providing complete description and traceability of their methods, whereas users must consider the effects of physiological, biometrical, preanalytical and analytical influences on the reference interval.

Evaluation of imprecision for cardiac troponin assays at low-range concentrations

BACKGROUND

The European Society of Cardiology/American College of Cardiology Committee for the Redefinition of Myocardial Infarction (MI) has recommended that an increased cardiac troponin should be defined as a measurement above the 99th percentile value of the reference group. A total imprecision (CV) at the decision limit of </=10% is recommended. However, peer-reviewed data on assay imprecision are lacking. The purpose of this study was to construct the clinically relevant imprecision profiles for each of the commercially available cardiac troponin assays. Pools of human sera containing cardiac troponin concentrations around the MI decision limit were assessed to identify the lowest concentration associated with a 10% CV.

METHODS

Eight serum pools targeting different concentrations of cardiac troponin (I and T) were prepared and stored at -70 degrees C until usage. The cardiac troponin measurement protocol consisted of two replicates per specimen per run, and one run per day for 20 days, using two reagent lots and three calibrations. Manufacturers of each cardiac troponin assay directly performed the measurements. Data analysis for each assay was centralized and performed according to the NCCLS EP5-A guideline.

RESULTS

The lowest concentrations (microg/L) providing a 10% CV were as follows: AxSYM, 1.22; ACS:180, 0.37; Centaur, 0.33; Immuno 1, 0.34; Access, 0.06; Vidas, 0.36; Liaison, 0.065; Dimension, 0.26; Opus, 0.90; Stratus CS, 0.10; Immulite, 0.32; Vitros ECi, 0.44; Elecsys, 0.04; AIA 21, 0.09.

CONCLUSION

No cardiac troponin assay was able to achieve the 10% CV recommendation at the 99th percentile reference limit defined by the manufacturer.

An evaluation of protein assays for quantitative determination of drugs

We have evaluated the response of six protein assays [the biuret, Lowry, bicinchoninic acid (BCA), Coomassie Brilliant Blue (CBB), Pyrogallol Red-Molybdate (PRM), and benzethonium chloride (BEC)] to 21 pharmaceutical drugs. The drugs evaluated were analgesics (acetaminophen, aspirin, codeine, methadone, morphine and pethidine), antibiotics (amoxicillin, ampicillin, gentamicin, neomycin, penicillin G and vancomycin), antipsychotics (chlorpromazine, fluphenazine, prochlorperazine, promazine and thioridazine) and water-soluble vitamins (ascorbic acid, niacinamide, pantothenic acid and pyridoxine). The biuret, Lowry and BCA assays responded strongly to most of the drugs tested. The PRM assay gave a sensitive response to the aminoglycoside antibiotics (gentamicin and neomycin) and the antipsychotic drugs. In contrast, the CBB assay showed little response to the aminoglycosides and gave a relatively poor response with the antipsychotics. The BEC assay did not respond significantly to the drugs tested. The response of the protein assays to the drugs was further evaluated by investigating the linearity of the response and the combined response of drug plus protein. The results are discussed with reference to drug interference in protein assays and the development of new methods for the quantification of drugs in protein-free solution.

[Biomarkers for toxicity and metabolic abnormalities of the main severe poisonings. Clinical and toxicologic symptoms. Conservative determination]

The members of the joint group "Toxicology and Clinical Biology" of the French Society of Clinical Biology (SFBC), the French Society of Analytical Toxicology (SFTA), and the Society of Clinical Toxicology (STC), suggest guidelines to meet the requirements of clinical biologists who are not specialized in toxicology. Based on good laboratory practice they propose a number of guidelines. Three synthetic tables have been established. They are not only toxicity biomarkers and metabolic disorders associated with the main severe intoxications, but also clinical signs that are observed during these intoxications, finally biological sampling as a precautionary measure. The table also takes into account approximately fifty xenobiotics: main clinical signs emergency, identification or quantification of the suspected product, useful biological markers, therapeutic, quantitations necessary to take into consideration patient care, and poison antidotes, are described. Recommendations regarding medical and forensic techniques are also proposed by the group. It is also necessary to collect and store biological samples when the individual patients are in charge. These samples will be analyzed or not depending on the individual case history.

Chylomicron remnant concentrations in patients with coronary artery disease

Persisting chylomicron remnants have been linked to premature atherosclerosis. The analysis of chylomicron remnant concentrations by an oral triglyceride tolerance test, however, is time-consuming for the study subjects and requires large resources in the laboratory. Therefore, only small numbers of subjects have been studied in the past. The aim of this study was to elucidate the prevalence of elevated chylomicron remnants, to identify effectors of chylomicron remnant clearance and to compare chylomicron remnants in the prediction of coronary artery disease with other risk factors. We applied a novel oral triglyceride tolerance test to 423 patients (368 males, 55 females) with a confirmed diagnosis of coronary artery disease (CAD) and to 390 control subjects (295 males, 95 females) in a case-control setting. This study revealed that elevated chylomicron remnant concentrations (retinyl esters > 1.5 micromol/l) are present in 20% of all subjects. Male gender, the apolipoprotein E2 isoform, and higher body mass index were associated with increased chylomicron remnant concentrations. However, chylomicron remnants were lower and plasma triglycerides higher in patients with CAD. We conclude that screening for a delayed clearance of chylomicron remnants is of little clinical value in CAD.