The new era of automated immunoassay.

Use of immunoassays and other ligand-binding assays in clinical diagnosis has increased dramatically during the last several years. Despite impressive technical advances, "mass production" of these assays in a routine laboratory still presents many difficulties. This review of ligand-binding assay technology highlights some recent developments, emphasizing challenges and possible solutions for cost-effective patient care.

Evaluation of CK-MB isoform analysis for early diagnosis of myocardial infarction.

Measurement of CK-MB and its isoforms by high-voltage electrophoresis has been proposed as a sensitive test for early detection of myocardial infarction (MI). We performed a prospective study of this test in 231 patients presenting to the Emergency Department with symptoms consistent with ischemic chest pain. Blood specimens were obtained at 0, 1, and 3 h following presentation, and plasma was immediately frozen and analyzed within 1 week by high-voltage electrophoresis for total CK-MB and isoforms. The test was considered positive whenever total CK-MB was elevated (>6 U/L) or the cardiac isoform MB2 was relatively increased (MB2 > 2 U/L and MB2/MB1 > 1.7). This test had a sensitivity of 68% overall and 55% for specimens collected within 3 h of symptom onset. It was positive within 3 h of presentation in 36/39 (92%) of patients with confirmed MI. Specificity was 92% overall and did not vary with time after symptoms. The CK-MB alone, at the cutoff of 6 U/L, had lower sensitivity overall (56%; p = 0.01) and within 3 h of onset (39%; p = 0.03), and higher specificity overall (98%; p < 0.001). Lowering the cutoff for CK-MB alone to match the sensitivity of the isoform test caused a greater loss of specificity. It is concluded that analysis of CK-MB by high-voltage electrophoresis is an effective method for rapid diagnosis of MI, with the isoform analysis enhancing early sensitivity.

Cardiac marker point-of-care testing in the Emergency Department and Cardiac Care Unit.

There has been much interest in improving the accuracy and speed with which chest pain patients presenting to the emergency department are diagnosed and treated. Recently, attention has been directed toward alternative site or point-of-care testing for biochemical markers of myocardial cell necrosis in addition to traditional diagnostic methodologies. The various point-of-care cardiac marker devices available and their potential applications are discussed. Regulatory and quality management issues related of point-of-care testing are reviewed.

Evaluation of a new assay for cardiac troponin I vs creatine kinase-MB for the diagnosis of acute myocardial infarction. Biochemical Markers for Acute Myocardial Ischemia (BAMI) Study Group.

OBJECTIVE: To compare a new assay for cardiac troponin 1 (cTn-1) with an assay for creatine kinase-MB (CK-MB) for the diagnosis of acute myocardial infarction (AMI). METHODS: A prospective cross-sectional study of patients presenting with symptoms consistent with cardiac ischemia was performed at a university teaching hospital. Serum sampling for cTn-1 and CK-MB was performed at 0, 1, 3, 8, and 16 hours after presentation. Normal values were defined as CK-MB < or = 7 ng/mL and a relative index < or = 2%, cTn-I < or = 1.4 ng/mL. Final diagnosis was made using World Health Organization criteria, including standard enzyme sampling. Consecutive patients with AMI were compared with a randomly selected subset of patients without AMI to determine the sensitivity and specificity of cTn-I and CK-MB assays for AMI, stratified by time from symptom onset. The ability of the biochemical cardiac markers obtained within 6 hours of symptom onset to predict later complications or need for interventions was assessed using odds ratios (ORs). RESULTS: Thirty-five patients who had AMI were compared with 136 patients who did not have AMI. The sensitivities and specificities of the cTn-I and CK-MB assays, stratified by time from symptom onset, were: [table: see text]. Patients who had elevations in either CK-MB or cTn-I within 6 hours of symptom onset were at increased risk for cardiovascular complications and/or interventions (CK-MB, OR 5.8; cTn-I, OR 6.3). CONCLUSION: cTn-I was as sensitive and specific for AMI as was CK-MB in ED patients who presented within 24 hours of symptom onset. However, cTn-I was more sensitive in patients who presented > or = 24 hours after symptom onset. Elevations of either marker within 6 hours of symptom onset predict an increased risk of complications and/or need for interventions.

Evaluation of cardiac STATus CK-MB/myoglobin device for rapidly ruling out acute myocardial infarction.

The Cardiac STATus CK-MB/Myoglobin device is highly sensitive and has a high negative predictive value within 3 hours of patient presentation. The device may play a role in the re-triage of patients from the CCU to less intensive settings, resulting in a net cost savings.

Evaluation of the Technicon Immuno 1 free thyroxine assay.

The Technicon Immuno 1 free thyroxine (fT4) assay, a modified two-step procedure that is fully automated on a random access analyzer, was evaluated-at two clinical sites. The method had excellent precision and correlated well overall with three other estimates of free thyroxine: free thyroxine index (FTI) measured on the Immuno 1; the Abbott IMx fT4 assay (Abbott Park, IL); and the Clinical Assays two-step manual fT4 assay. Using a combination of thyrotropin and FTI assay results as a "gold standard" for defining thyroid status, the Immuno 1 fT4 method had a sensitivity of 100% and specificity of 98.3% for hyperthyroidism, versus 93.8% and 99.3%, respectively, for hypothyroidism. In conclusion, the Immuno 1 fT4 assay is useful in screening for thyroid disease.

Improved specificity of myoglobin plus carbonic anhydrase assay versus that of creatine kinase-MB for early diagnosis of acute myocardial infarction.

STUDY OBJECTIVE: Carbonic anhydrase III (CA-III) is an enzyme released from skeletal muscle in a fixed ratio with myoglobin during cell injury, but unlike myoglobin it is not found in cardiac muscle. This study compared the clinical utility of serum myoglobin (S-Mgb) in conjunction with the ratio of S-Mgb to CA-III (S-Mgb/CA-III) versus creatine kinase-MB (CK-MB) for the early diagnosis of acute myocardial infarction (AMI). METHODS: This prospective observational study set at a university teaching hospital emergency department enrolled 251 consecutive consenting patients who presented with symptoms consistent with cardiac ischemia or infarction of less than 12 hours' duration. Patients with trauma or kidney failure were excluded. Standardized history and physical examination data were recorded, as were the results of serial blood sampling for S-Mgb, CA-III, and CK-MB at 0, 1, and 3 hours after patient presentation. A positive test for the study assays was defined as an S-Mgb concentration of more than 110 ng/mL with an S-Mgb/CA-III of 3.21 or higher by receiver operating characteristic analysis. Data were analyzed with McNemar's chi 2 test for symmetry and confidence intervals (CIs), using the exact method. RESULTS: Thirty (12%) of the 251 patients were found to have AMI by World Health Organization criteria. Mean time from symptom onset to presentation was 3.2 hours. The use of S-Mgb plus S-Mgb/CA-III compared with CK-MB for identification of AMI in patients presenting within 3 hours of symptom onset yielded respective sensitivities of 47.8% versus 17.4% (P = .02); specificities of 98.9% versus 100% (P = NS); positive predictive values of 84.6% (95% CI, 54.6% to 98.1%) versus 100% (95% CI, 39.8% to 100%); and negative predictive values of 93.5% (95% CI, 90.0% to 96.6%) versus 90.0% (95% CI, 84.8% to 93.9%). CONCLUSION: S-Mgb in conjunction with S-Mgb/CA-III was significantly more sensitive than CK-MB yet equally as specific for the early diagnosis of patients with AMI.

Evaluation of a new rapid quantitative immunoassay for serum myoglobin versus CK-MB for ruling out acute myocardial infarction in the emergency department.

STUDY OBJECTIVE: To compare the predictive values of serum myoglobin and creatine kinase (CK)-MB for ruling out acute myocardial infarction in the emergency department. DESIGN: Prospective, observational study. SETTING: University teaching hospital. PARTICIPANTS: One hundred eighty nine consecutive patients aged 30 years and older who presented within 12 hours from onset of chest discomfort, dyspnea, syncope, congestive heart failure, symptomatic dysrhythmia, pulmonary edema, or epigastric pain were entered into the study. Patients with trauma or renal failure were excluded. INTERVENTIONS: Standardized history and physical examination and blood sampling for serum myoglobin (S-Mgb) and CK-MB were done at the time of presentation (T0) and 1 hour later (T1). RESULTS: Using World Health Organization criteria, 22 acute myocardial infarction patients were identified. Mean time from symptom onset to presentation was 3.2 hours. S-Mgb was more sensitive than CK-MB at T0 and T1, 55% versus 23% (P < .05) and 73% versus 41% (P < .05), respectively. Respective specificities of S-Mgb versus CK-MB were 98% versus 99% (P = NS) at T0 and 97% versus 99% (P = NS) at T1. Negative predictive values of S-Mgb versus CK-MB were 94% versus 91% (P = NS) at T0 and 96% versus 93% (P = NS) at T1. The S-Mgb assay yielded quantitative results allowing the difference between the T0 and T1 values to be analyzed. A difference of 40 or more ng/mL between T0 and T1 was considered positive. When using a positive result in either the T0 or T1 value or a difference between the two values of 40 or more ng/mL, the sensitivity of S-Mgb was 91% (P < .05 versus CK-MB), the specificity was 96% (P = NS versus CK-MB), and the negative predictive value was 99% (95% confidence interval for S-Mgb, 97.0 to 100 versus CK-MB, 95% confidence interval, 88.9 to 96.6). CONCLUSION: In the first hour of presentation to the ED, the rapid quantitative assay for S-Mgb was statistically more sensitive than CK-MB and had an excellent negative predictive value for ruling out acute myocardial infarction in patients with typical or atypical symptoms. Due to the relatively small sample size, we could not exclude the possibility that differences in specificity might become statistically significant (beta error) with a larger sample size of acute myocardial infarction patients.

Effects of commonly prescribed nonsteroidal anti-inflammatory drugs on thyroid hormone measurements.

PURPOSE: To assess the effects of nonsteroidal anti-inflammatory drugs (NSAIDs) on thyroid function tests. PATIENTS AND METHODS: Eighty-nine patients receiving NSAIDs and 22 control subjects not taking NSAIDs were studied in a cross-sectional survey at Veterans Affairs and University hospitals. Measurements of serum thyroxine (T4), free T4 index, triiodothyronine (T3), and thyrotropin (thyroid-stimulating hormone [TSH]) were obtained for all subjects. RESULTS: Serum T4 measurements were lowered only in salsalate-treated patients, while serum T3 was depressed in patients receiving salsalate, diclofenac sodium, and naproxen. Serum T4 and T3 were unchanged in patients treated with diflunisal, ibuprofen, indomethacin, piroxicam, or sulindac. Serum TSH was normal in all subjects. CONCLUSIONS: Several NSAIDs can lower serum thyroid hormone concentrations, principally by interfering with the binding of T4 and T3 to serum carrier proteins; patients taking these drugs remain euthyroid. Awareness of these interactions may prevent unnecessary diagnostic or therapeutic interventions.

Metabolic profiling of amniotic fluid by proton nuclear magnetic resonance spectroscopy: correlation with fetal maturation and other clinical variables.

Proton NMR spectroscopy at 600 MHz was performed on 70 specimens of human amniotic fluid, representing pregnancies at different stages of maturation and with different fetomaternal complications. Spectra with good signal-to-noise characteristics were obtained in 3.5 min of acquisition time, directly on untreated fluid, with presaturation to suppress the intense water resonance. Metabolites that generally gave rise to well-resolved resonances included lactate, glucose, creatinine, choline derivatives, citrate, acetate, alanine, glycine, glutamate, succinate, and others. For three of these metabolites--creatinine, glucose, and lactate--the peak intensities correlated well with results of conventional chemical analysis. The NMR spectra of third-trimester specimens were readily distinguishable from those of second-trimester specimens, and several peak intensities correlated with fetal maturation during the third trimester. Significant correlations with maternal preeclampsia and fetal open spina bifida were also observed.

Current issues in maternal serum alpha-fetoprotein screening.

Measurement of maternal serum alpha-fetoprotein originated in the early 1970s as a means to screen for fetal neural tube defects, a relatively common and devastating class of malformations. Since that time, assay methods have improved, interpretation has been refined, follow-up testing for neural tube defects has advanced, and many other disease associations have been uncovered. It is a unique test, both in its clinical application and its laboratory implementation. The present review outlines current procedures for maternal serum alpha-fetoprotein screening and summarizes recent developments.

25Mg NMR studies of magnesium binding to erythrocyte constituents.

The binding of Mg2+ ion to ATP, ADP, AMP, 2,3-bisphosphyoglycerate (DPG), and hemoglobin has been studied by 25Mg NMR spectroscopy at 9.4 T. Addition of any of these ligands to a solution of 2 mM 25MgCl2 at pH 7.2 caused a progressive increase in linewidth, with no discernible chemical shift. ATP and ADP, which form tight 1:1 complexes with Mg2+, did not cause maximal broadening until present in several-fold excess, implying that bis(nucleotide) complexes also form. The studies showed progressively weaker Mg2+ binding to ATP, ADP, DPG, and AMP, consistent with published binding constants. Hemoglobin cause fairly little broadening, consistent with its known weak affinity for Mg2+. Competition studies determined ATP affinities for Ca2+ and H+ that were also in good agreement with published values. 25Mg NMR spectra of 2 mM bound 25Mg2+ were obtained with good signal to noise in less than 1 hr. The technique may now be a practical means for studying the binding of Mg2+ within erythrocytes and other cells.

Diagnosis of ectopic pregnancy by the rate of increase of choriogonadotropin in serum: diagnostic criteria compared.

We compare three methods for using the rate of change of human choriogonadotropin (hCG) concentration in serum to diagnose ectopic pregnancy. With Method I, the lower limit for the rate of increase of serum hCG in normal pregnancy is 66% per 48 h. With Method II, a different lower limit of normal is specified for each of four discrete sampling intervals of hCG. With Method III, the lower limit of normal is determined by a continuous discriminant function of the initial hCG concentration. If the initial hCG concentration is less than or equal to 2000 int. units/L (Second International Standard), all three methods have acceptable diagnostic efficiencies, and there are no statistically significant differences among conclusions from the methods. None of the three methods performs satisfactorily if the initial hCG concentration is greater than 2000 int. units/L. We recommend Method I because it is simpler than the other two.

Evaluation of a sensitive immunoenzymetric assay for maternal-serum alpha-fetoprotein screening. Comparison with radioimmunoassay.

An automated immunoenzymetric assay (IEMA) using monoclonal antibodies (Tandem-E, Hybritech) was evaluated for maternal serum alpha-fetoprotein (MSAFP) testing, in comparison with a classical radioimmunoassay (RIA) (Clinical Assays). The IEMA was superior in terms of sensitivity, precision, and linearity. Systematic bias between the two methods resulted in a narrower spread of clinical results, expressed as multiple-of-median, with the IEMA. Consequently, the IEMA produced fewer results that by usual criteria would be considered high (suggesting increased risk of neural tube defect) or low (suggesting increased risk of Down's syndrome). Although both methods may be comparably suitable for neural tube defect screening, the IEMA is advantageous for Down's syndrome risk assessment.