Use of creatine kinase MB isoenzyme for diagnosing myocardial infarction when total creatine kinase activity is high

The usefulness of measuring creatine kinase MB isoenzyme for diagnosing myocardial infarction when activities of total creatine kinase are very high is unclear. We conducted a retrospective study in an urban hospital that serves a largely indigent population. We concentrated on 146 patients whose creatine kinase activity was greater than 1000 U/L (upper limit of normal: 165 U/L for women and 225 U/L for men), with MB isoenzyme greater than 10 U/L and less than 5% of total creatine kinase. The positive predictive value of MB isoenzyme (isoimmune method) values greater than 10 U/L was between 11.6% and 56.8% when the value for total creatine kinase exceeded 1000 U/L. Using different values (MB greater than 4% of total creatine kinase) as positive for myocardial infarction would have resulted in far fewer false-positives, but 10 cases of myocardial infarction would have been missed. The most appropriate cutoff value for MB isoenzyme in this population (total creatine kinase greater than 1000 U/L) was found to be greater than 2% of total creatine kinase.     

Detection of cardiac-specific creatine kinase isoenzyme in sera with normal or slightly increased total creatine kinase activity.

We describe a spectrophotometric kinetic assay for detecting creatine kinase MB isoenzyme activity in the 1 to 10 U/liter range. The MB isoenzyme was isolated [Clin. Chem. 20, 36 (1974)] and assayed (Rosalki method) with an Abbott ABA-100. Good reproducibility was demonstrated for MB isoenzyme activities near 1 U/liter (CV = 2.6%). Sera with normal or slightly increased total creatine kinase activity were evaluated. Sera of 14 patients with acute myocardial infarction contained, per liter, 84 to 236 U of total creatine kinase activity and 4.6 to 28.0 U of isoenzyme MB activity; corresponding ranges for sera from healthy lab technicians and patients with noncardiac disease were 36 to 277 and 0 to 2.6 U. MB isoenzyme activity for infarction patients rose and fell sharply within three days after the infarction. Atypical time-course patterns, MB isoenzyme activity remaining abnormally great for five days, were observed in serum from patients with prolonged atrial fibrillation and congestive heart failure or cardiomyopathy; the BB isoenzyme (1 to 5 U/liter) was also detected in sera of such patients but was absent in sera from infarcation patients. Quantification of column-isolated MB by the assay described is rapid, easy, specific, and extremely sensitive for measuring MB in the 1 to 10 U/liter range.     

Comparison of catalytic activity and mass concentration of serum creatine kinase MB isoenzyme in the detection of coronary reperfusion in acute myocardial infarction after therapeutic thrombolysis

Serum creatinine kinase MB isoenzyme time-activity curves are useful for the assessment of coronary reperfusion after acute myocardial infarction. The purpose of this study was to compare serum creatine kinase MB catalytic activity with mass concentration for the determination of coronary reflow after therapeutic thrombolysis. Creatine kinase MB mass was determined immunoenzymometrically. Creatinine kinase MB catalytic activity concentration was determined by electrophoresis. Serum was collected every 4 hours for 96 hours in two groups of myocardial infarction patients: A (n = 10), urokinase induced reperfusion; B (n = 10), conventional therapy without urokinase. Peaks of mass and activity occurred at similar times in groups A and B. Both were significantly earlier in the urokinase treated patients. The maximal rate of increase of creatine kinase MB (based on either mass or catalytic activity) was threefold greater in the urokinase group. There are no important differences between the behaviour of creatine kinase measured as catalytic concentration or as mass concentration. Mass concentration is therefore equally useful as an indicator of coronary reperfusion.     

Determination of creatine kinase isoenzyme MB activity in serum using immunological inhibition of creatine kinase M subunit activity. Activity kinetics and diagnostic significance in myocardial infarction.

This is a new method for the determination of creatine kinase isoenzyme MB activity in serum. The method uses direct activity measurement of creatine kinase B subunit activity after blocking of CK-M subunit activity by inhibiting antibodies. The test takes no longer than 15 min. The method yields an intra-serial C.V. of 2.0-12.9%, and a C.V. from day to day of 5.5%. The detection limit is 3.4 U/l creatine kinase MB. In the 95 cases with proven myocardial infarction several types of creatine kinase MB activity kinetics could be determined. The percentage of creatine kinase MB of peak CK-total is 6-25%, with a mean of 11.1%. The amount of creatine kinase MB with respect to total CK activity after reinfarction is higher than the amount after initial infarction.     

Chromatographic and electrophoretic separation of creatine kinase isoenzymes compared.

We compared two techniques for separating and evaluating serum creatine kinase isoenzymes--fluorometric agarose electrophoresis and Sephadex chromatography--in 50 patients, 25 of whom had confirmed acute myocardial infarction. In every case isoenzyme MB (heart isoenzyme) was detected with equal sensitivity by either procedure. Evidently, only the presence or absence of MB is clinically significant; none of the 25 patients without infarction had detectable MB activity in their serum. Columns connected to a continuous-flow sample line for analyses of the eluting stream without further modification produced satisfactory results.     

Evaluation of a commercial immunoenzymometric assay kit for creatine kinase MB isoenzyme determination using monoclonal antibodies

A simultaneous two-site immunoenzymometric assay for creatine kinase MB determination (Hybritech Tandem-E CK-MB) using monoclonal antibodies was evaluated and compared with cellulose acetate electrophoresis using fluorometric scanning densitometry. The assay has satisfactory precision (between-day analysis gives a coefficient of variation between 2.1 and 9.4%) and is not susceptible to interference by concentrations of creatine kinase MM up to 5000 micrograms/l (3400 U/l) and creatine kinase BB up to 1000 micrograms/l (1085 U/l). The upper limit of MB isoenzyme concentration in 250 apparently healthy people was 5.5 micrograms/l. Comparison between the immunoenzymometric assay (y) and electrophoresis (x) yielded the following linear regression equation: y = 0.37x + 1.9, with a correlation coefficient of 0.828. The characteristics of the temporal kinetics of MB isoenzyme, calculated by two methods, in 49 patients with acute myocardial infarction, were nearly identical in terms of the rate of creatine kinase MB release and the time at which the peak value is obtained, but not in terms of the rate of elimination of the isoenzyme. The fractional disappearance rate of MB isoenzyme from the circulation was significantly higher if calculated with Tandem-E results rather than with electrophoresis results (-0.035 vs -0.028, p less than 0.001). Whereas in the first day after infarction immunoenzymometric assay and electrophoresis had the same clinical sensitivity for identifying patients with acute myocardial infarction, in specimens collected more than 24 hours after the onset of the chest pain, the clinical sensitivity of the immunoenzymometric method was lower. Our results show that it is still premature to draw definitive clinical conclusions from the immunoassay results.     

Atypical increase in serum creatine kinase activity in hospital patients.

We use an ion-exchange column-chromatographic technique for separating creatine kinase isoenzymes in serum, and occasionally observe what appears to be sustained increase in the MB fraction. Most patients whose sera show such behavior have myocardial disease, but not necessarily a recent myocardial infarction. Electrophoretic analysis of a small sampling of such sera revealed that the apparent MB migrates atypically, appearing distinctly between isoezymes MB and MM. In another electrophoretic system, the peak might easily be mistaken for MM. This unusual isoenzyme does not appear to be "macro" creatine kinase. In laboratories that use the ion-exchange technique, the possibility of a falsely positive MB value should be considered in subjects who show persistent increases together with normal or nearly normal values for total creatine kinase activity. A suitable electrophoretic method that clearly demonstrates this unusual isoenzyme should be used in such cases, for confirmation.     

Raised CK-MB isoenzyme after exercise in a patient with alcoholic myopathy

The relation between exercise, total serum creatine kinase activity, and serum creatine kinase MB isoenzyme in a patient with alcoholic myopathy was investigated. After a short-term exercise the serum values of creatine kinase MB isoenzyme rose to high levels within hours. This finding is important for obvious differential diagnostic reasons.     

Systemic short-term fibrinolysis with high-dose streptokinase in acute myocardial infarction: time course of biochemical parameters

The course of plasma catalytic activities of total creatine kinase, creatine kinase isoenzyme MB, total, cytoplasmatic and mitochondrial aspartate aminotransferase, alanine aminotransferase, lactate dehydrogenase, alpha-hydroxybutyrate dehydrogenase, glutamate dehydrogenase and concentrations of myoglobin, urea, acidic alpha 1-glycoprotein and creatinine were followed in 33 patients suffering from acute myocardial infarction. All patients were randomized in a double-blind, prospective study. One group (18 patients) was infused with streptokinase 1.5 X 10(6) units/90 minutes; the control group received routine continuous i.v. heparin treatment (1000 units/h). Ten hours after completion of the study protocol, treatment of both groups of patients was continued with heparin, 1000 units/h and Aspisol, 1 g/day2). Streptokinase treatment induced earlier wash-out and therefore earlier peak levels of several enzymes: total creatine kinase (11 hours), creatine kinase isoenzyme MB (6 hours), total and cytoplasmatic aspartate aminotransferase (6 hours) and lactate dehydrogenase (9 hours). Total creatine kinase peak catalytic activity and myoglobin peak concentration were higher in the group receiving thrombolytic therapy. A significantly different course of catalytic activity between both treatment groups was found for total creatine kinase and creatine kinase isoenzyme MB, total and cytosolic aspartate aminotransferase, lactate dehydrogenase and alpha-hydroxybutyrate dehydrogenase. The course of mitochondrial aspartate aminotransferase catalytic activity was different only 12 hours after the beginning of treatment. The shift of several catalytic activities to an earlier peak level in plasma may indicate reperfusion of ischaemic myocardium due to thrombolytic therapy.     

New manual and automated method for determining activity of creatine kinase isoenzyme MB, by use of dithiothreitol: clinical applications.

The method is based on the selective activating capacity of dithiothreitol on creatine kinase isoenzyme MB, after isoenzyme MM is activated by glutathione. Isolated isoenzymes MM and MB of human and canine origin were assayed individually and in mixtures of known activities. When glutathione was present in the assay medium the activity of each isoenzyme could be measured individually, but glutathione did not activate isoenzyme MB if it was present in a mixture with MM. Dithiothreitol, added to the serum before assay, activated the isoenzyme MB in the mixture. Values for MB activities obtained for isolated isoenzyme MB and for the isoenzyme mixture after dithiothreitol was added averaged 110 and 111 U/liter, respectively (r = 0.998; y = 1.007 x + 0.298; n = 10). In the serum of 40 patients with documented acute transmural myocardial infarction, the mean proportion of isoenzyme MB activity measured in this way was 5.5% (coefficient of variation, 7.7%). Isoenzyme MB activities measured by use of dithiothreitol compared well with those obtained by conventional electrophoresis/spectrophotometry (r = 0.998; y = 1.09x -0.65) and spectrofluorometry (r = 0.996; y = 1.10 x + 0.80). The assay of MB activity by the dithiothreitol method was automated, by use of an Abbott Bichromatic Analyser and a Calbiochem Super-Stat Pack Kit. In 60 isoenzyme MB determinations the manual and automated method correlated well (r = 0.990; y = 1.0x -1.36). The simplicity of isoenzyme MB determination by use of dithiothreitol and its ease of automation allow routine monitoring of the isoenzyme activity in patients with ischemic heart disease.     

A simplified method for purification of the creatine kinase isoenzyme of human brain (BB)

A greatly simplified procedure has been developed for purification in high yields of creatine kinase isoenzyme BB from human brain. The procedure consists of fractional precipitation with ethanol, adsorption chromatography on hydroxylapatite, and fractional precipitation with ammonium sulfate. The essentially homogeneous enzyme obtained may be used as the antigen for radio immunoassay of blood isoenzyme MB of creatine kinase, which specifically increases following myocardial infarction.     

A "column-batch" method for separating MB and LD1 in a single fraction

In this "column-batch" method for separating the MB and BB isoenzymes of creatine kinase and the LD1 isoenzyme of lactate dehydrogenase, one can, alternatively, separate MB from BB or obtain a combined fraction containing MB, BB, and LD1. The principal advantage is that the resulting fractions are twofold as concentrated as was the applied sample. Thus, activity can be measured by conventional automated methods, with no need for the modifications to compensate for diluted fractions that are required by other ion-exchange methods. Another advantage is the total absence of interference by the MM isoenzyme. A strong anion exchanger (AG-MP1, Bio-Rad) is used in the acetate form at pH 6.3. There is no retention of MM; retained MB, BB, and LD1 are eluted with a solution of magnesium acetate. Results are compared with those obtained for subunit B and LD1 by immunoinhibition. Results with patients are considered consistent with myocardial infarction if MB exceeds 20 U/L and 3% of the total CK and LD1 exceeds 130 U/L or 28% of the total LD activity.     

Creatine kinase and lactate dehydrogenase isoenzymes in serum of patients suffering burns, blunt trauma, or myocardial infarction

Medical records of 53 burn and trauma patients were reviewed to assess the possibility of myocardial damage. Except for electrophoretically detectable creatine kinase MB isoenzyme, none showed evidence of myocardial injury. Lactate dehydrogenase isoenzyme tests, electrocardiograms, myocardial pyrophosphate scans, clinical course, and results of (two) autopsies were all negative for myocardial necrosis or ischemia. Types of patient, number, mean peak value (U/L) for serum creatine kinase, and ranges of percentage MB isoenzyme were as follows. Burns from direct electrical contact: 28, 16 600, 0-29; electrical flash or other thermal burns: 10, 4340, 0-22; blunt trauma (mostly from automobile accidents): 15, 3430, 0-18; myocardial infarction: 57, 1520, 4-46. Evidently creatine kinase MB isoenzyme is nonspecific in burn and trauma patients and should not be the only test result used to assess myocardial involvement.     

Improved column method for separating lactate dehydrogenase isoenzymes 1 and 2

Lactate dehydrogenase (LD) isoenzymes 1 and 2 in human serum were separated on a column of diethylaminoethyl-Sephadex. Samples layered on mini-columns were eluted with buffered sodium chloride (100, 150, and 200 mmol/liter). Lactate dehydrogenase activity in column effluents was measured by the Wacker method, and their isoenzyme content was evaluated by electrophoresis on polyacrylamide gel. Results for column-fractionated LD-1 and LD-2 were expressed in two ways: LD-1/LD-2 ratios and total LD-1 + LD-2 activities. The former is a more specific indicator of myocardial infarction than the latter. Sera from 10 patients with acute myocardial infarction (increased creatine kinease isoenzyme MB activity) exhibited ratios in the range of 0.92 to 1.56, ratios for 10 patients without heart disease (normal creatine kinase MB) ranged from 0.33 to 0.69.     

Stability and electrophoretic characteristics of creatine kinase BB extracted from human brain and intestine

Creatine kinase (CK; EC 2.7.3.2) isoenzyme BB extracted from brains of rats reportedly undergoes modification at 37 degrees C, leaving an electrophoretic variant that accounts for most of the residual CK activity. This variant, called CK-BB', migrates on electrophoresis similarly to creatine kinase isoenzyme MB. Using electrophoresis and immunoinhibition with antiserum to creatine kinase isoenzyme MM, we found CK-BB to be the only identifiable cytoplasmic isoenzyme in surgical samples from human brain and intestine. In contrast, we found that some samples of brain obtained at autopsy contain CK-BB'. We also found that CK-BB extracted from human brain was converted to CK-BB' upon incubation in serum or plasma at 37 degrees C. We found a similar development of CK-BB' in incubation mixtures of serum or plasma containing CK-BB obtained from surgical samples of human intestine. The development of CK-BB' during infarction of the gastrointestinal system may thus be a source of false-positive CK-MB in the laboratory verification of myocardial infarction when electrophoresis is used as the only method to identify CK isoenzymes.     

Etude de la myoglobinemie et de son evolution au cours de l'infarctus du myocardeStudy on myoglobinemia and its development during myocardial infarction

Thirty six patients suffering from myocardial infarction were investigated by assay of their serum myoglobin, total creatine kinase and creatine kinase isoenzyme MB activities. Determination of serum myoglobin presents, with regard to creatine kinase MB, two major advantages: a very early increase after the onset of the pain (about three hours later) and a very quick clearance, allowing the diagnosis of a second episode of necrosis after about one day.     

Serum creatine kinase isoenzyme MB activity: Evaluation of a kit employing agarose-gel electrophoresis with overlay paper fluorescence scanning

A commercial kit for determining serum creatine kinase isoenzyme MB activity was evaluated. The kit employed agarose-gel electrophoresis followed by incubation of overlay paper on the agarose and then fluorescence scanning of the paper. Within-day coefficients of variation ranged from 24.9% for a specimen with no elevation of MB activity to 6.6% for a specimen with moderately elevated MB activity. The kit appeared to demonstrate MB in all sera and showed higher than expected values in recovery studies. The kit performed in a relatively linear fashion from 50 to 500 I.U./1 total creatine kinase activity. Hemolysis appeared to lower measured MB. For comparison with another method, specimens were also analyzed by microcolumn chromatography, which was found to incompletely separate isoenzymes. The kit produced lower values than microchromatography for specimens with low MB activities and higher values for specimens with elevated MB activities. Patients without corroborative evidence of myocardial injury showed a somewhat hyperbolic relationship between per cent MB and total creatine kinase activity, but MB activity was generally 4 I.U./1 or less. Although the kit had serious laboratory shortcomings, it may be as clinically useful as other methodologies.     

Creatine kinase isoenzyme variants in human serum

In serum from about 800 patients, total creatine kinase and its subunit B activities were determined by the recommended Scandinavian creatine kinase method in the absence and presence of a creatine kinase M subunit inhibitory antibody. Eight patients had supranormal subunit B activities, but normal or near-normal values for total creatine kinase activity. Electrophoresis of sera from these eight patients showed, in addition to the normally migrating isoenzyme MM, one or two abnormally migrating creatine kinase isoenzyme bands, located between normally migrating isoenzymes MM and MB. Experimental data suggest that these abnormal bands may be isoenzyme BB with changed electrophoretic mobility. The eight patients had no particular disorder in common.     

Apparent elevation of serum CK-MB not due to acute myocardial infarction.

An increased serum level of the MB isoenzyme of creatine kinase (CK-MB) is a useful marker for acute myocardial infarction. Although described extensively in clinical chemistry literature, there is little information in standard medical references about false positives for this test. We report two cases where high levels of measured CK-MB activity were in fact due to another form of CK, associated with internal malignancy.     

APPARENT ELEVATION OF SERUM CK-MB NOT DUE TO ACUTE MYOCARDIAL INFARCTION

An increased serum level of the MB isoenzyme of creatine kinase (CK-MB) is a useful marker for acute myocardial infarction. Although described extensively in clinical chemistry literature, there is little information in standard medical references about false positives for this test. We report two cases where high levels of measured CK-MB activity were in fact due to another form of CK, associated with internal malignancy.