Standardization of creatine kinase-MB (CK-MB) mass assays: the use of recombinant CK-MB as a reference material

BACKGROUND

The AACC assembled a committee to identify and validate a standard creatine kinase MB isoenzyme (CK-MB) material to improve the comparability of CK-MB mass assays.

METHODS

Three protocols were used. In protocol I, various CK-MB materials prepared in different matrices were screened as candidate standards. In protocol II, participating manufacturers calibrated their systems with concentrates of human heart CK-MB and then tested 20 patient samples to evaluate calibration bias. In protocol III, participating manufacturers calibrated their immunoassay systems using recombinant CK-MB2 (rCK-MB2) diluted into their respective sample diluents and measured 50 samples.

RESULTS

Candidate materials showed high recovery in stripped human serum, but bias improved only from 59% to 38%. These data led to the use of human heart CK-MB diluted in each manufacturer's sample diluent. This strategy reduced bias from 31% to 15%. Because human heart CK-MB is difficult to provide, a lyophilized source of CK-MB2 was identified. rCK-MB2 was shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, reversed-phase HPLC, intrinsic protein fluorescence, circular dichroism, agarose gel electrophoresis, immunoreactivity studies, high and low temperature stability, and reconstituted stability to be equivalent to human heart CK-MB. Calibration of immunoassay systems with rCK-MB2 added into each respective manufacturer's sample diluent showed a 13% between-manufacturer bias.

CONCLUSION

Lyophilized rCK-MB2 was determined suitable for use as a reference material for CK-MB mass assays.

Homocysteine screening of a female Hispanic population

A total of 821 women of Hispanic descent aged 21-65 years, were screened for total and high density lipoprotein (HDL) cholesterol through outpatient clinics and public screening. Of this group, 78 were invited back for further testing because they had a total cholesterol/HDL cholesterol ratio exceeding 4.5 indicative of high risk for cardiovascular disease. Written consent and a fasting blood sample was obtained from these women, and tested for serum homocysteine. The concentrations for 77 of the 78 women (mean 8. 40+/-2.24, range 4.21-13.99 micromol/l) were within the pre-established normal range for women. One subject had an exceptionally high homocysteine concentration of 137 micromol/l. This subject subsequently developed a stroke and has been institutionalized since that time. Blood from the subject and immediate family members were tested for the 5'-10'-methylenetetrahydrofolate reductase (MTHFR) polymorphism. The subject and her children were both hyperhomocysteinemic and heterozygous for the mutation. One of the children also had a low vitamin B12 concentration in blood. Although the high homocysteine and cardiovascular risk in these subjects were likely due to a dietary deficiency of the vitamins, the MTHFR mutation may have also been a contributing factor. With the availability of rapid assays, screening blood for homocysteine in subjects deemed at high risk for cardiovascular disease may be justified.

Proposals from the IFCC Committee on Standardization of Markers of Cardiac Damage (C-SMCD): strategies and concepts on standardization of cardiac marker assays

The search for sensitive and specific biochemical markers of cardiac damage has resulted in development of methods for the measurement of cardiac markers such as myoglobin, CK-MB mass and the cardiac troponins (cardiac troponin I and cardiac troponin T). There have been new clinical applications of already known markers based on improved, reformulated methods which often depend on advanced technologies. These developments are connected with analytical and interpretative challenges for the laboratory manager and for the clinician. In this situation, it is essential that international professional societies develop comprehensive and carefully elaborated guidelines for the quality management and use of these measurements and their results. Several professional associations have formed committees working on different issues regarding the measurement of biochemical markers of cardiac damage. Recognizing the huge interest in this field and substantial diagnostic relevance of these markers, the IFCC has established the Committee on "Standardization of Markers of Cardiac Damage" (C-SMCD) in 1997 inviting the already operating American and European groups to designate some of their members into the new committee. The task of the IFCC C-SMCD is to coordinate the different activities of the national groups, with preparation of international documents and recommendations under the auspices of IFCC and to initiate various standardization activities. The establishment of consensus/reference methods as well as development of primary and secondary matrix reference materials for markers of cardiac damage are extremely important in order to achieve comparability of test results, thus leading to an effective patient care.

Biochemical markers of cardiac damage: from traditional enzymes to cardiac-specific proteins. IFCC Subcommittee on Standardization of Cardiac Markers (S-SCM)

Measurement of cardiac markers in blood has been the mainstay for diagnosis of acute myocardial infarction for nearly 50 years. The field has evolved from measurement of enzyme activity to mass concentrations of proteins using automated non-isotopic immunoassays. With changing clinical practices, cardiac markers are now needed to detect the presence of minor myocardial infarction in patients with unstable angina. Outcome studies have shown that patients with increased troponin are at high short-term risk for death and AMI. Recent developments involve the use of cardiac markers to select the most appropriate therapy for patients with acute coronary syndromes. The success of new cardiac markers such as troponin is due to their high cardiac specificity and the existence of assays with low detection limits. Traditional enzymes such as CK and CK-MB are thought to be released only in situations of irreversible myocardial necrosis. In the case of cardiac troponin, clinical observations and animal studies suggest that cytosolic free troponin may be released in reversible ischemia in addition to irreversible cell damage. The IFCC S-SCM has recommended use of two cut-off concentrations for cardiac troponin to differentiate normal from minor myocardial injury and AMI. A low cut-off may detect reversible ischemic events in some cases.

Proposals from IFCC Committee on Standardization of Markers of Cardiac Damage (C-SMCD): recommendations on use of biochemical markers of cardiac damage in acute coronary syndromes

This paper presents evidence and suggestions from the IFCC C-SMCD on the use of biochemical markers for the triage diagnosis of acute coronary syndromes. There is general agreement that both 'early' and 'definitive' biochemical markers are necessary and that these assays must be available with a turnaround time of 1 h or less. Currently, myoglobin is the marker that most effectively fits the role as an 'early' marker, whereas 'definitive' markers are cardiac troponins. Since the sensitivity of the initial electrocardiogram is only 50% for detecting myocardial infarction, the use of biochemical markers may significantly contribute to the early diagnosis. New sensitive biochemical markers, particularly the cardiac troponins, are presently the best criterion to detect the presence of small myocardial cell damage. Two decision limits are probably needed for the optimum use of troponins: a low abnormal value suggesting the presence of myocardial damage and a higher value suggesting the diagnosis of myocardial infarction. Additional studies should be performed to establish limits for each commercially available assay. Finally, it is recognized that there is no need for the use of any biochemical marker when the clinical diagnosis is unequivocal, other than for diagnosing reinfarction, estimating the infarct size, and monitoring thrombolytic therapy.

Applications of forensic identity testing in the clinical laboratory

DNA analysis is becoming routine in the clinical laboratory for the diagnosis of human diseases using various tissue sources. Most clinical specimens are followed by tracking forms that include patient demographic data, accession number, and date and time of collection. As part of a thorough quality assurance program, proper documentation of test requisitions and tracking forms is mandatory. Despite these efforts, specimen mislabeling or other mix-ups can, and do, occur. We demonstrate the utility of the PM + DQA1 typing kit and STR analysis using the Visible Genetics automated DNA sequencing system in the proper identification of such clinical specimens as urine, blood, and paraffin-embedded tissues. In each case, sufficient DNA was extracted from these specimen types using a nonorganic extraction protocol for typing purposes. We conclude that DNA typing methods are feasible for distinguishing clinical laboratory specimens of questionable identity and compliment existing quality assurance techniques.

Adulteration of urine by "Urine Luck"

BACKGROUND

In vitro adulterants are used to invalidate assays for urine drugs of abuse. The present study examined the effect of pyridinium chlorochromate (PCC) found in the product "Urine Luck".

METHODS

PCC was prepared and added to positive urine controls at concentrations of 0, 10, 50, and 100 g/L. The controls were assayed for methamphetamine, benzoylecgonine (BE), codeine and morphine, tetrahydrocannabinol (THC), and phencyclidine (PCP) with the Emit II (Syva) and Abuscreen Online (Roche) immunoassays, and by gas chromatography/mass spectrometry (GC/MS). Two tests were also developed to detect PCC in urine: a spot test to detect chromate ions using 10 g/L 1,5-diphenylcarbazide as the indicator, and a GC/MS assay for pyridine. We tested 150 samples submitted for routine urinalysis, compliance, and workplace drug testing for PCC, using these assays.

RESULTS

Response rates decreased at 100 g/L PCC for all Emit II drug assays and for the Abuscreen morphine and THC assays. In contrast, the Abuscreen amphetamine assay produced apparently higher results, and no effect was seen on the results for BE or PCP. The PCC did not affect the GC/MS recovery of methamphetamine, BE, PCP, or their deuterated internal standards, but decreased GC/MS recovery of the opiates at both intermediate (50 g/L) and high (100 g/L) PCC concentrations and apparent concentrations of THC and THC-d3 at all PCC concentrations. Two of 50 samples submitted for workplace drug testing under chain-of-custody conditions were positive for PCC, whereas none of the remaining 100 specimens submitted for routine urinalysis or compliance drug testing were positive.

CONCLUSIONS

PCC is an effective adulterant for urine drug testing of THC and opiates. Identification of PCC use can be accomplished with use of a spot test for the oxidant.

National Academy of Clinical Biochemistry Standards of Laboratory Practice: recommendations for the use of cardiac markers in coronary artery diseases

The Sixth Conference on the "Standards of Laboratory Practice Series", sponsored by the National Academy of Clinical Biochemistry (NACB), was held on August 4-5, 1998, at the Annual Meeting of the American Association for Clinical Chemistry, in Chicago, IL. An expert committee was assembled to write recommendations on the use of cardiac markers in coronary artery diseases. The NACB Committee prepared a preliminary draft of the guidelines, made them available on the World Wide Web (www.nacb.org), and distributed them before the presentations. The recommendations were divided into four areas: the use of markers in the triage of patients with chest pain, acute coronary syndromes, clinical applications other than acute myocardial infarction and research, and assay platforms and markers of acute myocardial infarction. The recommendations were revised and subsequently re-presented in part at the "Biomarkers in Acute Cardiac Syndromes Conference", sponsored by the Jewish Hospital Heart and Lung Institute, Louisville KY, on October 16-17, 1998. This report lists each recommendation, its scientific justification, and a summary of discussions from conference participants and reviewers. Approximately 100 individuals responded to various versions of these recommendations via direct correspondences, telephone calls to Committee members, electronic mail correspondence to the Committee Chairman, or oral questions and comments raised during one of the two conference presentations. Some of the recommendations were changed to reflect the consensus opinion. In cases in which there was no consensus, the Committee included pertinent discussion without necessarily changing the original recommendations. At times, the Committee members felt that although a particular recommendation might not be the current standard of care today, they anticipate that it likely will be adopted in the near future.

Release of cardiac troponin in acute coronary syndromes: ischemia or necrosis?

Analysis of cardiac troponin T and I have been shown to be effective in detecting minor myocardial injury in cardiac patients who present with acute coronary syndromes (ACS). Determination of minor myocardial injury is significant, as these patients have a higher short-term morbidity and mortality than other unstable angina patients with normal concentrations for these markers. In this report, two theories are given as to why cardiac troponin is superior to other markers such as CK-MB for risk stratification. The 'low cut-off concentration model' is based on the fact that troponin is not increased in patients with skeletal muscle disease or injury, resulting in low baseline concentrations of the cardiac isoforms in the absence of active cardiac disease. This enables the use of low decision limits. Troponin also has a higher myocardial tissue content relative to CK-MB, thereby also increasing its clinical sensitivity to irreversible injury. In the 'reversible ischemia model', cytoplasmic free troponin T and I leak across the membrane of myocytes as the result of reduced coronary blood flow. Jeopardized myocardial tissue can recover with acute recanalization. Support for this model comes from clinical observations and animal studies.

Use of biochemical markers in acute coronary syndromes. IFCC Scientific Division, Committee on Standardization of Markers of Cardiac Damage. International Federation of Clinical Chemistry

This paper presents evidence and suggestions from the IFCC Committee on "Standardization of Markers of Cardiac Damage" (C-SMCD) on the use of biochemical markers for the triage diagnosis of acute coronary syndromes. There is general agreement that both 'early' and 'definitive' biochemical markers of myocardial damage are necessary and that these assays must be available with a turnaround time of 1 h or less. Currently, myoglobin is the marker that most effectively fits the role as an 'early' marker, whereas 'definitive' markers are cardiac troponins. Since the sensitivity of the initial electrocardiogram is only 50% for detecting myocardial infarction, the use of biochemical markers may significantly contribute to the early diagnosis and become relevant when the electrocardiogram is not diagnostic. In addition, new sensitive biochemical markers, particularly the cardiac troponins, are presently the best to detect the presence of minor myocardial cell damage. With regard to this, two decision limits are probably needed for the optimal use of troponins: a low abnormal value suggesting the presence of myocardial damage and a higher value suggesting the diagnosis of myocardial infarction according to traditionally used criteria. Properly designed studies should be performed to establish limits for each commercially available troponin assay. Finally, it is recognized that there is no need for the use of any biochemical marker when the clinical diagnosis is unequivocal, other than for diagnosing reinfarction, estimating the infarct size, and monitoring thrombolytic therapy.

Minimal standards for the performance and interpretation of toxicology tests in legal proceedings

There have been several high profile criminal and civil cases that have been litigated in recent years involving toxicologic analyses and interpretations of blood, urine, and other specimens for drugs of abuse. Disputes have erupted between prominent toxicologists and laboratory scientists as to the validity and interpretation of the data presented. The disputes centered around the fact that the procedures used in these cases had not been properly validated with analytical noise being misinterpreted as a positive result. As with any analyses, forensic tests must be conducted in a manner such that they meet the minimum standards accepted within the toxicology community. No conclusions as to presence or absence of drug, its concentration, or its physiologic effects can be made if there is a failure to meet these basic standards. Several cases are presented where these standard tenets may not have been followed.

A comparison of cardiac troponin T and cardiac troponin I in patients with acute coronary syndromes

The majority of studies have shown that the performance of assays for cTnT and cTnI is almost identical in detecting AMI in patients with coronary artery disease. Currently cTnT may have an advantage over cTnI because available laboratory and POC platforms are standardized to a single reference material. Nevertheless, the decision to use cTnT or cTnI a given laboratory will probably be made on the basis of cost and the availability of automated instrumentation within that institution, and not necessarily on assay performance. A laboratory is unlikely to purchase an instrument to perform a single test. Because cTnI will soon be available on all commercial immunoassay analyzers, it seems likely that cTnI will become the analyte of choice.

Quantitative determination of cholesterol in lipoprotein fractions by electrophoresis

The Helena REP cholesterol profile system (Helena Laboratories, Beaumont, TX) separates VLDL, LDL, HDL and Lp(a) by agarose gel electrophoresis, and quantitates cholesterol by enzymatic staining and densitometry. We compared results by electrophoresis to combined ultracentrifugation/precipitation (beta-quantification, BQ) for VLDL, LDL, and HDL cholesterol and to immunonephelometry for Lp(a) mass (Behring Diagnostics, Westwood, MA) in serum from 64 patients with a variety of lipid disorders. There was good agreement between methods, with a mean bias of -0.19 (-7.3), 0.09 (3.5), and 0.09 (3.4) mmol/l (mg/dl) for VLDL, HDL, and LDL cholesterol for electrophoresis vs. BQ. These differences were significant for HDL and VLDL cholesterol (P < 0.001), but not for LDL cholesterol measurement (P > 0.05). There was also good correlation between methods with coefficients of 0.83, 0.92, 0.91, and 0.97 for VLDL, HDL, Lp(a), and LDL, respectively. Our data indicate that this method can accurately and precisely measure LDL cholesterol directly in fresh serum from patients with a wide range of triglyceride values. However, HDL cholesterol measurement did not meet NCEP guidelines for precision and accuracy. Also, the poor resolution of VLDL and LDL in some specimens is a concern.

Meta-analysis: dietary fat intake, serum estrogen levels, and the risk of breast cancer

BACKGROUND

There is compelling evidence that estrogens influence breast cancer risk. Since the mid-1980s, dietary fat intervention studies have been conducted to investigate the effect of fat intake on endogenous estrogen levels. To further our understanding of the possible relationship between dietary fat and breast cancer, we conducted a meta-analysis of dietary fat intervention studies that investigated serum estradiol levels, and we reviewed the nature of the evidence provided by prospective analytic studies of fat consumption and breast cancer risk.

METHODS

A computerized search of the English language literature on estrogen/estradiol and dietary fat intervention studies published from January 1966 through June 1998 was conducted using the MEDLINE database. Pooled estimates were derived from the change in estradiol levels associated with fat reduction from 13 studies. Analyses were conducted separately for premenopausal and postmenopausal women and in both groups combined.

RESULTS AND CONCLUSIONS

Statistically significant reductions in serum estradiol levels of -7.4% (95% confidence interval [CI] = -11.7% to -2.9%) among premenopausal women and -23.0% (95% CI = -27.7% to -18.1%) among postmenopausal women were observed, with an overall -13.4% (95% CI = -16.6% to -10.1%) reduction observed. The greatest reductions occurred in two studies in which dietary fat was reduced to 10%-12% of calories compared with 18%-25% of calories in the other studies. A statistically significant reduction in estradiol levels of -6.6% (95% CI = -10.3% to -2.7%) remained after exclusion of these two studies. Review of prospective analytic epidemiologic studies that allowed for dietary measurement error suggests that the possibility that reducing fat consumption below 20% of calories will reduce breast cancer risk cannot be excluded.

IMPLICATIONS

Dietary fat reduction can result in a lowering of serum estradiol levels and such dietary modification may still offer an approach to breast cancer prevention.

Simultaneous rapid measurement of whole blood myoglobin, creatine kinase MB, and cardiac troponin I by the triage cardiac panel for detection of myocardial infarction

This multicenter study evaluated the Biosite Triage(R) Cardiac Panel as a quantitative, multimarker, whole blood system for the detection of acute myocardial infarction (MI). Optimum cutoffs for the discrimination of acute MI (n = 192 patients, 59 with MI) as determined by ROC curve analyses were as follows: 0.4 microgram/L for cardiac troponin I (cTnI); 4.3 microgram/L for the creatine kinase MB isoenzyme (CK-MB); and 107 microgram/L for myoglobin. The Triage Panel showed the following concordances for detection or rule-out of MI compared with established devices: cTnI >89%; CK-MB >81%; myoglobin >69%. No significant differences were present between methods for the same marker. Diagnostic efficiencies demonstrated comparable sensitivities and specificities for the diagnosis of MI in patients presenting with symptoms compared with the Dade, Beckman, and Behring CK-MB, cTnI, and myoglobin assays; the ratio of sensitivity to specificity for each marker was as follows: cTnI, 98%:100%; CK-MB, 95%:91%; myoglobin, 81%:92%. The areas under the ROC curves for the Biosite myoglobin, CK-MB, and cTnI were 0.818, 0.905, and 0.970, respectively; the areas were significantly different, P <0.05. In patients with skeletal muscle injury and renal disease, the Triage cTnI showed 94% and 100% specificity, respectively. The Triage panel offers clinicians a whole blood, point-of-care analysis of multiple cardiac markers that provides excellent clinical sensitivity and specificity for the detection of acute MI.

Reflex testing I: algorithm for lipid and lipoprotein measurement in coronary heart disease risk assessment

We reviewed the current literature in order to construct a reflex testing algorithm that maximizes clinical utility and cost-effectiveness of lipid and lipoprotein testing. The algorithm was based on the 2nd Report of the National Cholesterol Education Program Adult Treatment Panel guidelines for use of total cholesterol (TC), triglycerides (TG), HDL-C, and LDL-C, and published reports describing the clinical use of apolipoprotein B and lipoprotein (a). The success of this algorithm was tested in a low-risk general and a high-risk hyperlipidemic patient population. Lipid data and non-lipid risk factors were obtained from a national database and from patients seen at two lipid clinics. A total of 16,968 individuals from the National Health and Nutrition Examination Survey III database comprised the low-risk group, and 239 patients examined in the Hartford Hospital and Washington University Lipid Clinics comprised the high-risk group. We found a solid scientific base to support the NCEP guidelines and reasonable support for limited testing of apoB and Lp(a). According to the algorithm, the direct LDL-C assay was deemed unnecessary in 98% and 91% of low- and high-risk subjects, respectively, if one assumes that the Friedewald equation is adequate with TG < or = 4.00 g/l. With a more conservative cutoff of TG < or = 2.50 g/l, the algorithm canceled 92% and 81% of direct LDL tests, respectively. The algorithm also limited TG to 20 and 64%, apoB to 6 and 20%, and Lp(a) to 15 and 56%, of low- and high-risk groups, respectively. Use of a comprehensive, reflex algorithm for coronary heart disease risk assessment will substantially reduce the utilization of laboratory services without diminishing the clinical value of these tests. The algorithm will prevent the overuse of certain expensive tests (direct LDL) while promoting the limited use of underutilized tests [apoB and Lp(a)].

Cardiac markers: from enzymes to proteins, diagnosis to prognosis, laboratory to bedside

For many years, serologic markers have been used to assist cardiologists in the diagnosis and management of patients with cardiovascular diseases. The use of laboratory markers has evolved and kept pace with the field of cardiology itself. The early markers involved testing for total enzyme activity such as aspartate aminotransferase, lactate dehydrogenase and creatine kinase. Shortly thereafter, the World Health Organization included serial enzyme markers as part of the triad for diagnosis of acute myocardial infarction (AMI). It was soon recognized that isoenzymes such as for CK-MB and LD-1 provided more specific organ specificity. The need for reporting rapid results led to the development of totally automated isoenzyme assays, which have evolved from immunoinhibition (INH) techniques to mass assays. The current emphasis for cardiac markers is use of protein markers such as cardiac troponin T (cTnT) and I (cTnI). These markers are more sensitive and specific than isoenzyme markers and enable risk stratification for non-AMI patients with unstable angina: patients with high troponin have a higher risk for AMI and cardiac death within the immediate future (4 to 6 weeks). Prospective management of cardiac patients requires more rapid testing and reporting of results. Point-of-care testing platforms on whole blood are now available for emergency testing at bedside.

Soy intake and risk of breast cancer in Asians and Asian Americans

Evidence from case-control studies suggests, although not entirely consistently, that soy intake may protect against breast cancer. The designs and findings of studies conducted in Asian women living in Japan, Singapore, China, and the United States are reviewed. Because of the considerably higher intake of soy by native Asians than by Asian Americans living in California and Hawaii, these studies investigated different segments of the dose-response relation between soy intake and breast cancer risk. Data are not sufficient to determine the amount or frequency of soy intake effective in protecting against breast cancer. Of concern is that soy intake may be homogeneously high in Asia, making it difficult to identify differences in breast cancer risk between high and moderate daily consumers. In studies conducted in Asian Americans, it is difficult to be certain that soy intake is not a marker of other factors related to Western lifestyle that are causally associated with risk of breast cancer. Additional studies assessing the role of soy and breast cancer are needed. These studies should assess intake of all food sources of soy, considering portion size as well as other dietary and nondietary factors that may confound the soy-breast cancer association. A better understanding of the mechanisms whereby soy intake may influence the risk of breast cancer is also needed. Dietary intervention studies with soy will provide information on the acute effects of soy on endogenous hormone concentrations. Cross-sectional and longitudinal studies are necessary to investigate the longer-term relations between hormone concentrations and soy intake in women.

Improved GC/MS analysis of opiates with use of oxime-TMS derivatives

An improved gas chromatographic/mass spectrometric (GC/MS) assay is described for the quantitation of codeine and morphine as trimethylsyl (TMS) derivatives. The TMS derivatization of ketone-containing opiates results in the formation of multiple derivatives. Some of these products have retention times close to those of codeine-TMS and morphine-TMS. When the keto-opiates are present in samples assayed for codeine and morphine in urine, they can interfere with the quantitation of these commonly targeted opiates. The assay was improved with the addition of a pre-BSTFA derivatization step, whereby hydroxylamine was used to convert the keto-opiates into the corresponding oxime derivative. These derivatives were then reacted with BSTFA to form the TMS ethers and TMS oxime derivatives. The oxime step enabled production of single derivatives for hydrocodone and hydromorphone. In addition, the retention times for the oxime-TMS derivatives were increased so that they no longer elute near the targeted drugs of codeine and morphine. The addition of the oxime step does not affect the sylation of codeine and morphine, and the accuracy and precision of this assay were unaffected.

Biochemical differences between cTnT and cTnI and their significance for diagnosis of acute coronary syndromes

Although assays for cardiac troponin T (cTnT) and cardiac troponin I (cTnI) exhibit similar clinical performance in patients with acute coronary syndromes for diagnosis and risk stratification, there are differences in the release and clearance of these proteins from damaged myocytes. There are also differences in the percentages of patients with chronic renal failure and skeletal muscle myopathies that have abnormal results. A review of the biochemistry of these proteins may provide insights as to the nature of these differences. Cardiac troponin T has a higher overall tissue concentration and free cytoplasmic concentrations than cTnI, and appears in blood of patients with acute myocardial infarction as a mixture of complexed (cTnT-I-C) and free cTnT. Cardiac troponin I is more hydrophobic and appears in blood predominately in the binary complex (I-C) form, with smaller amounts of the ternary (T-I-C) complex. Degradation of the complex will lead to faster clearance of the protein. There are also differences in standardization and availability of commercial troponin kits. Cardiac troponin T assays are available from only one manufacturer and are standardized to a single material, whereas cTnI is available from multiple vendors. While there is some degree of correlation between assays, there are significant proportional biases between results which can be problematical when different tests are made on the same patient.

Seroprevalence of Helicobacter pylori infection in patients with hepatitis B

Helicobacter pylori infection has been investigated extensively in immunocompromised hosts, such as those with acquired immunodeficiency syndrome (AIDS) and organ transplant recipients. However, few reports on H. pylori prevalence in individuals with chronic HBV infection are available. The aim of this serological study is to investigate H. pylori prevalence in patients with hepatitis B. Ninety-six consecutive hospitalised patients with chronic hepatitis B were studied, together with 104 age-matched healthy individuals of similar socioeconomic status and with no evidence of hepatitis B virus infection or liver diseases. Serum samples from both groups were tested for specific IgG antibodies to H. pylori, using enzyme-linked immunosorbent assay (ELISA). Of the 96 patients with hepatitis B, 55 (57.3%) were positive for serum IgG anti-H. pylori, significantly greater than in the control group of 104, where 44 (42.3%) were positive (P < 0.05). In addition, the seroprevalence of H. pylori in the 45 patients who were positive for hepatitis B envelope antigen (HBeAg) and/or HBV-DNA was 75.6% (34), compared to 41.2% (21) in the 51 patients who were negative (P < 0.005). An increase in H. pylori prevalence is present in patients with chronic hepatitis B. Further study is needed to determine whether eradication of H. pylori will benefit these patients.

The effect of pathologic substances and adulterants on the DNA typing of urine

Human urine has not been adequately investigated as a potential source of DNA for forensic identity testing. The advent of polymerase chain reaction technology has made possible the analysis of previously undetectable levels of nucleic acids from human urine and other body fluids lacking nucleated cells. In this study, we evaluated the ability to genotype DNA extracted from adulterated urine specimens using the AmpliType PM + DQA1 PCR amplification and typing system. Fresh, first-void male urine specimens were contaminated with household bleach, E. coli, human serum albumin, glucose and saponin (a strong detergent). All of the adulterated samples were typed without difficulty. Frozen male urine specimens were split into equal volumes; one aliquot was adulterated with either E. coli or saponin, and the other was left free of contaminants. Seventy-one percent of all frozen urine specimens tested (adulterated and unadulterated) were successfully typed using this amplification and typing system. Our data, therefore, suggest that the AmpliType PM + DQA1 PCR amplification and typing system described is suitable for genotype analysis of adulterated fresh and frozen urine specimens.