Influence of autoantibodies to creatine kinase-BB on assays for MB isoenzyme

We describe the influence of autoantibodies that bind creatine kinase BB (CK-BB) on the methods for MB isoenzyme. If these autoantibodies are present in patients' sera, they cause the formation of macro CK type 1 (immunoglobulin-linked CK-BB). In some of these cases they can bind not only endogenous CK-BB but also CK-MB without significantly affecting enzyme activity. Although these antibodies show distinctly less affinity for CK-MB than for CK-BB, they nevertheless bind CK-MB in these particular sera, because their concentration exceeds that of CK-BB isoenzyme. If a person with such autoantibodies has an acute myocardial infarction, the immunoinhibition method for CK-MB, which does not discriminate between CK-MB and CK-BB, will recognize the increase and peak of CK-MB with time, although persistent macro CK activity will be superimposed on the typical isoenzyme pattern. However, isoenzyme electrophoresis and recently introduced immunoenzymometric assays for CK-MB in these cases may be less sensitive for detecting myocardial infarctions, because the typical increase in CK-MB activity may be identified later in the progression of symptoms, or even be missed.     

Creatine kinase isoenzymes in human cerebrospinal fluid and brain

Extracts of normal brains obtained at autopsy and cerebrospinal fluid (CSF) from patients with global brain ischemia were analyzed for creatine kinase (CK; EC 2.7.3.2) isoenzymes. We used both qualitative and quantitative assays (electrophoresis and immunoinhibition). Brain extracts contained CK-BB isoenzyme and mitochondrial CK. In 54 CSF samples free of blood contamination and with total activities ranging from 7 to 2010 U/L (mean 202 U/L), virtually all of the CK activity was due to CK-BB, and none to CK-MM or CK-MB. We conclude that brain contains CK-BB and mitochondrial CK, but lacks CK-MM and CK-MB. After cardiac arrest, CK-BB is released into the CSF. Any CK-MM in the CSF is probably from blood contamination, in which case immunoinhibition with anti-CK-M antibodies accurately quantifies CK-BB.     

A sensitive bioluminescent immunoinhibition test for CK-B subunit activity and a CK-MB specific ELISA compared: correlation with agarose electrophoresis and influence of CK-isoenzyme profile on results

Searching for alternatives to the imprecise spectrophotometric tests for low-concentration creatine kinase (EC 2.7.3.2) isoenzyme MB (CK-MB), we investigated the analytical performance of two potentially superior approaches--a bioluminescent immunoinhibition assay (I, LKB-Wallac) and an ELISA (enzyme-labeled immunosorbent assay) technique (II, Hybritech)--in comparison with an electrophoretic method (III, Beckman). Only I showed good between-day precision (CV 8.3%) at the upper reference limit, allowing reproducible assay of CK-B subunit activity down to at least 3 U/L. In conditions where CK isoenzyme assays remained unaffected by CK-MM concentrations, test results were proportional to the amount of CK-MB in the sample up to at least 50 U/L for I, 120 micrograms/L for II, and 100 U/L for III (r greater than 0.998 by linear regression analysis). For CK-MB-positive samples, the data by I correlated more closely with values by III (n = 24; r = 0.994) than did results by II (n = 15; r = 0.909), but both methods were equally effective in discriminating between samples with or without electrophoretically supranormal CK-MB activity (93% sensitivity). II was entirely CK-MB specific, whereas CK-B activity by I was consistently (18/18) increased in CK-MB-negative samples containing CK-BB (n = 6; r = 0.996) or macro CK, types 1 or 2 (n = 12; r = 0.930). I is highly sensitive for screening for increased non-MM CK activity, the nature of which should be subsequently clarified by electrophoresis.     

Evaluation of a new automated system for the determination of ck-mb isoforms

We evaluated a new analyzer (Cardio REP) specifically designed for cardiac CK-MB isoenzyme and isoforms activity, with a performance time of 24 minutes. Ten AMI patients, with times elapsed between the onset of chest pain and admission to hospital ranging from 30 minutes to 4 hours, were monitored every 3–4 hours until the 16th hour of hospitalization. In each serum sample, in addition to total CK-MB and CK-MB isoforms measured by the Cardio REP analyzer, we also assayed total CK activity, CK-MB activity by immunoinhibition method, CK-MB mass concentration, CK-MB isoforms by REP method, troponin T, and myoglobin. The precision study demonstrated acceptable within assay and between assay CVs% for total CK-MB (8.1 and 10.4), MB₁ (9.1 and 14.2), and MB₂ (9.1 and 8.2) isoforms. The method was found to be linear up to 371 U/L for MB₂ isoform fraction and up to 516 U/L for total CK-MB. Results for CK-MB obtained with the Cardio REP correlated well with those for CK-MB activity obtained with the immunoinhibition method (r = 0.869) and those of CK-MB mass concentration (r = 0.923). The sensitivity of the Cardio REP CK isoforms method was found to be greater than that of the REP CK isoforms method. Time to first increased value of MB₂/MB₁ ratio and MB₂ isoform was earlier in comparison to that for CK-MB mass concentrations and similar to that for myoglobin, a marker that, however, lacks specificity. The diagnostic efficiency of CK-MB isoforms and the availability of a real-time, fully automated method for their measurement suggest the utilization of this biochemical marker in emergency for the early diagnosis of AMI.     

Quantifying the MB isoenzyme of creatine kinase with the Abbott "IMx" immunoassay analyzer

In this two-step automated assay of the MB isoenzyme of creatine kinase (CK-MB), developed for the Abbott "IMx" immunoassay analyzer, monoclonal anti-CK-MB antibody immobilized onto latex microparticles and polyclonal anti-CK-MM antibody coupled to alkaline phosphatase are used. Within-run CVs ranged from 3.9% to 9.0%, between-run CVs from 0.0% to 5.6%, and the sensitivity was 0.2 microgram/L. Twenty-four results can be obtained in about 37 min. Analytical recovery of CK-MB added to human serum or plasma ranged from 89% to 109%. Icteric, lipemic, or hemolyzed samples did not interfere with CK-MB recovery. Cross-reactivity with CK-MM and CK-BB was 0.012% and 0.001%, respectively. The normal reference interval was 0-5 micrograms/L. IMx CK-MB results correlated well with CK-MB enzyme activity as determined by electrophoresis (n = 203; r = 0.97; slope = 0.90; y-intercept = -4.29) and with commercial immunoassays. We think that this assay will be useful for confirmation of acute myocardial infarction, both in critical-care units and in the clinical laboratory.     

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.     

Mass concentration of creatine kinase MB isoenzyme and lactate dehydrogenase isoenzyme 1 in diagnosis of perioperative myocardial infarction after coronary bypass surgery

Recent advances in methodology allow the mass concentration of creatine kinase MB isoenzyme (CK-MB), and of lactate dehydrogenase isoenzyme 1 (LD1) to be determined quickly and easily as routine, emergency tests. We evaluated these tests as diagnostic criteria of perioperative myocardial infarction (PMI) after coronary bypass surgery. These tests were compared with the usual measurements of CK-MB activity by immunoinhibition and LD1 by electrophoresis and with other biological markers of myocardial infarction such as total CK, total LD, and aspartate aminotransferase. Sixty-one patients who underwent coronary bypass grafting were followed pre- and postoperatively by enzyme determinations and electrocardiography; a subgroup was monitored by myocardial scintigraphy. CK-MB mass appeared to be the best marker of PMI during the first 48 h, although LD1 was the marker of choice from days 2 to 4.     

Immunochemiluminometric assay of creatine kinase MB with a monoclonal antibody to the MB isoenzyme

Previous two-site immunometric assays for creatine kinase (CK; EC 2.7.3.2) MB isoenzyme have been based on formation of a "sandwich" complex involving CK-MB and antibodies that recognize the CK-MM and the CK-BB isoenzymes. Single-incubation model assays of CK-MB with these antibodies were susceptible to interferences by CK-MM and CK-BB. We produced two anti-CK-MB monoclonal antibodies and studied their suitability for two-site assays. Both antibodies were compatible with anti-CK-MM and anti-CK-BB, but not with each other. Using anti-CK-MB as the tracer antibody eliminated the interference by both CK-MM and CK-BB. Labeling anti-CK-MB with acridinium ester and immobilizing anti-CK-BB on paramagnetic particles, we developed a rapid and highly sensitive chemiluminescent/magnetic separation CK-MB assay. As little as 1 microgram of CK-MB per liter was detectable after 10- or 30-min incubation at room temperature, and the standard curve was linear up to 400 micrograms/L. Results for serum samples by the new assay correlated well (r = 0.94) with those by Corning electrophoretic and the Hybritech Tandem-E immunoenzymometric CK-MB methods. Sera containing macro CK-1 or high concentrations of CK-MM and CK-BB did not interfere. The combined advantages of a more-specific antibody, paramagnetic solid phase, and chemiluminescent label endow this two-site CK-MB assay with performance characteristics and ease of use superior to those of previous assays.     

Immunoenzymetric assay for creatine kinase MB with subunit-specific monoclonal antibodies compared with an immunochemical method and electrophoresis

Results of an immunoenzymetric assay (TANDEM-E CKMB) for creatine kinase (CK; EC 2.7.3.2) MB isoenzyme, in which subunit-specific monoclonal antibodies are used, were compared with those by an immunochemical method (Isomune-CK) and electrophoresis (Corning agarose gel). The study involved 200 patients; greater than 500 samples were analyzed by all three methods. The analytical performances were acceptable. Between-method correlation coefficients ranged from 0.881 to 0.975. Two reference intervals were established for the immunoassays: 0-4 micrograms/L (TANDEM) and 0-4 U/L (Isomune) for "normal" patients; 0-9 micrograms/L (TANDEM) and 0-14 U/L (Isomune) for noninfarct patients. Agreement with respect to increased CK-MB as defined by the reference intervals for the noninfarct patient was 96% between TANDEM and electrophoresis, 90% between Isomune and electrophoresis. All three methods are acceptable for use in determining CK-MB, but the overall diagnostic efficiencies for the mass or activity concentration of the isoenzyme and for its proportion of total CK activity, based on the predictive value model, are 92% (electrophoresis, 0-7 U/L), 90% (electrophoresis, 0-4%), 92% (TANDEM, 0-9 micrograms/L), 88% (TANDEM, 0-3% index), 88% (Isomune, 0-14 U/L), and 83% (Isomune, 0-4%). All three methods can detect CK-MB in serum, but its presence is not necessarily diagnostic of acute infarct. We recommend using the actual concentration of CK-MB to evaluate patients with suspected acute myocardial infarct, and the percentage of CK-MB when total CK is very high.     

Transient increase in serum creatine kinase isoenzyme BB activity after prostatectomy in a patient with massive benign prostatic hyperplasia

The activity of creatine kinase isoenzyme BB (CK-BB) in serum is rarely abnormally high (i.e., detectable). An increase in immunoreactive CK-BB or CK-BB activity in patients with prostatic disease has been proposed as an indication of prostatic adenocarcinoma. Here we report the case of an elderly man with massive benign prostatic hyperplasia but no clinical or pathological evidence of prostatic adenocarcinoma, whose serum CK-BB activity was found by agarose gel electrophoresis to be 1 U/L (normal: 0%), 10% of his total CK activity. Serum CK-BB activity was further increased to 16 U/L (20% of total CK activity) 1 h after prostatectomy, but became undetectable by the second day after the operation. The findings suggest that: (a) the source of the serum CK-BB activity was the enlarged prostate gland; (b) abnormally high CK-BB activity in serum of men with prostatic disease does not necessarily indicate the presence of prostatic adenocarcinoma; and (c) myocardial injury could be erroneously diagnosed postoperatively in prostatectomy patients if CK isoenzyme methods are used that do not consistently separate "heart-specific" CK-MB from CK-BB.     

Diagnostic efficacy of a new enzyme immunoassay for creatine kinase MB isoenzyme

A new commercial enzyme immunoassay kit for quantification of creatine kinase-MB (CK-MB) isoenzyme was compared with its electrophoretic determination with respect to efficacy in diagnosis of acute myocardial infarction. Enzygnost CK-MB (Behring Diagnostics) is a solid-phase "sandwich"-type enzyme immunoassay with antibodies to the B-subunit coated on plastic tubes and peroxidase-conjugated antibodies to the M-subunit added after incubation with sample. This kit is designed to measure only CK-MB and not CK-MM, CK-BB, adenylate kinase, or atypical CK molecules. The linear-regression equation comparing the two methods was: Enzygnost = 0.98 . electrophoresis - 0.72, with a correlation coefficient of r = 0.967 (n = 143). For 51 patients admitted for diagnosis of possible acute myocardial infarction, the Enzygnost kit achieved 100% sensitivity, specificity, and efficiency in predicting the correct diagnosis. Corresponding values for the electrophoretic assay were: 95.5% sensitivity, 93.1% specificity, and 94.1% efficiency. We conclude that this kit method provides an excellent alternative to electrophoresis.     

Creatine kinase isoenzyme MB assay by electrophoresis

A method for determination of the creatine kinase isoenzyme MB (CK-MB) is reported: separation of the isoenzymes was done by electrophoresis and the activity of the isoenzyme bands quantitated by scanning fluorometry. Total CK activity was used for calculation of CK-MB level. The precision of the method was satisfactory: coefficient of variation 5-10%. Its accuracy good: CK-MB was consistently found in high concentrations in tissue extracts of myocardium, but was virtually absent in skeletal muscle and could not be demonstrated in serum from patients with skeletal muscle damage. The sensitivity of the method fitted its clinical use: CK-MB was undetectable (less than 5 U/l) in normal sera, below 30 U/l in seventy-six out of seventy-seven patients in whom the diagnosis of acute myocardial infarction (AMI) was disproved, and above 30 U/l in all seventy-two patients with AMI according to WHO criteria. The CK-MB concentration in serum rises to a maximum about 20 h after onset of clinical symptoms of AMI and reaches baseline levels 20-30 h later. The electrophoretic CK-MB method is easy, fast and reliable and is considered as an important diagnostic test for AMI.     

Semi-automated direct colorimetric measurement of creatine kinase isoenzyme MB activity after extraction from serum by use of a CK-MB-specific monoclonal antibody

This semi-automated colorimetric assay for the MB isoenzyme of creatine kinase (EC 2.7.3.2) is based on a monoclonal antibody ("Conan-MB") specific for this isoenzyme and is a modification of a previously published method (Vaidya et al., Clin Chem 1986;32:657-63). A 0.64-cm bead coated with 2 to 3 micrograms of antibody is incubated with 100 microL of serum and 10 microL of 0.2 mol/L beta-mercaptoethanol for 1 h at room temperature, to extract CK-MB. The beads are washed with de-ionized water and incubated with CK substrate for 45 min at 37 degrees C. A solution containing trans-1,2-diaminocyclohexane-N,N,N', N'-tetraacetic acid, p-iodonitrotetrazolium violet, and diaphorase is added and the resulting colored product is measured at 492 nm. The standard curve is linear to 200 U of CK-MB per liter, and analytical recovery is 97-113%. Total assay CV for low (9.7 U/L) and high (50.7 U/L) quality-control materials was 14.1% (n = 1878) and 11.6% (n = 1842), respectively. CK-MB activity correlated well (r = 0.978, n = 226) with CK-MB measured by a two-site mass immunoassay, and 99.4% of samples with CK-MB greater than or equal to 12 U/L (n = 347) were verified by electrophoresis on agarose.     

A novel CK isoenzyme migrating between CK-MB and CK-BB

A CK isoenzyme migrating between CK-MB and CK-BB was detected in the serum of three patients with metastatic prostatic carcinoma. CK-BB was detected in the serum of all three patients and mitochondrial CK in two of the patients. Total CK activity was either normal or elevated, and the atypical CK isoenzyme, CK-BB and the mitochondrial CK isoenzyme were present in serum for up to 1.5 months. This atypical CK isoenzyme was not CK-MB, an albumin-ligand complex, or adenylate kinase, and was not bound to an immunoglobulin. This atypical CK isoenzyme did not contain immunologically normal CK-M subunits but had some CK-B subunits and could be a variant CK-BB or CK-MB isoenzyme. Its appearance in serum could be indicative of a serious illness.     

Clinical effectiveness of the Du Pont aca measurement of creatine kinase MB in serum from patients in a coronary-care unit

We evaluated the clinical effectiveness of measuring creatine kinase (CK; EC 2.7.3.2) isoenzyme MB and lactate dehydrogenase (LD; EC 1.1.1.27) isoenzymes in diagnosis of acute myocardial infarction. We used an agarose electrophoresis method to measure CK and LD isoenzymes and the Du Pont aca column method to measure CK-MB. Serial blood specimens were drawn from 100 patients consecutively admitted to our Coronary Care Unit. Because of the low diagnostic specificity for CK-MB measurements by both agarose electrophoresis and the discrete-analysis method, as compared with reported values, we re-evaluated our isoenzyme data by using Receiver Operating Characteristic curves. Such analysis of the data established optimal decision levels of greater than or equal to 25 U/L and greater than or equal to 18 U/L plus greater than or equal to 6% of total CK for serum CK-MB measured by the agarose electrophoresis and the aca methods, respectively, and an optimal decision level of greater than or equal to 0.92 for the ratio of LD 1/2 measured after agarose electrophoresis. At these decision levels we obtained a sensitivity of 100%, 100%, and 95% and a specificity of 94%, 92%, and 90% for CK-MB (agarose electrophoresis), CK-MB (aca), and the LD 1/2 ratio, respectively.     

At what level of serum total creatine kinase activity can measurement of serum creatine kinase MB isoenzyme activity be omitted in suspected myocardial infarction?

The purpose of this study was to establish a discriminatory limit for serum total creatine kinase activity (CK activity) below which CK isoenzyme fractionation is unnecessary. We looked at 2610 serum samples from 1077 consecutive patients with suspected acute myocardial infraction (AMI). The CK activity was determined according to the Scandinavian recommended method. Isoenzymes of CK were separated by agarose gel electrophoresis, followed by fluorometric scanning. When the threshold for CK activity was 150 U/l, none of the samples had a creatine kinase MB isoenzyme activity (CK-MB activity) equal to or higher than 30 U/l (the diagnostic level), which has been found to differentiate between patients with AMI and those without AMI. Only 14 patients (1.3% of all patients investigated) had CK-MB activity peaks between 10 U/l (detection limit) and 30 U/l. Of these, AMI was only diagnosed in one. We recommend that CK-MB activity should be measured only when CK activity is higher than 150 U/l. This would make about 50% of all CK-MB measurements unnecessary.     

Validation of NACB and IFCC guidelines for the use of cardiac markers for early diagnosis and risk assessment in patients with acute coronary syndromes

BACKGROUND: International guidelines have been established for the use of cardiac markers in the early diagnosis and risk assessment of patients with acute coronary syndromes. METHODS: A single center, prospective observational study was conducted in a tertiary care university hospital on 200 consecutive patients with suspected acute myocardial infarction (AMI). Blood was drawn on admission and after 2, 4, 8, 12 and 24 h for the measurement of CK-MB/CK activity, myoglobin, CK-MB mass and troponin I. A 6-week follow-up was undertaken for the combined end point of acute coronary syndrome and death. RESULTS: Myoglobin showed an early diagnostic sensitivity of 0.65 on admission, 0.90 after 2 h and 0.92 after 4 h compared with 0.46, 0.74 and 0.88 for CK-MB/CK activity. The combination of myoglobin and cTnI increased the diagnostic value compared with myoglobin alone on admission, 2 and 4 h later. In multivariate analysis, cTnI and CK-MB/CK mass, but not myoglobin and CK-MB/CK activity, were shown to be independent predictors on the 6-week follow-up. CONCLUSIONS: Repetitive myoglobin measurements within 4 h of admission, combined with at least one early troponin test, was shown to be the strategy of choice in early AMI diagnosis and prognosis assessment.     

Immunochemical extraction and automated measurement of plasma creatine kinase MB isoenzyme and creatine kinase MB2 isoform

Measurement of creatine kinase MB (CK-MB) and its isoforms CK-MB₂ and CK-MB₁ are now applied in the diagnosis of acute myocardial infarction (AMI). The most common approach for analysis includes RIA, IRMA, and electrophoresis, all of which may be time-consuming. This study examines determination of CK-MB and CK-MB₂ by a rapid immunochemical extraction method followed by an automated measurement for both analytes. The automated method was sensitive to 2 U/L, linear to 180 U/L, and gave excellent interassay precision (<10% CV). Interference studies indicated that bilirubin, hemolysis, and lipemia caused analytical problems as did the presence of high activities of other CK isoenzymes, notably CK-MM and CK-BB, requiring dilution of samples prior to analysis. Application of immunochemical extraction gave a reference interval of CK-MB (0–2.5 U/L) and CK-MB₂ (0.1–1.4 U/L) for blood donors (20–60 years), peak levels for ruled-out AMI patients of CK-MB (0.5–7.3 U/L) and CK-MB₂ (0.3–4.9), peak levels for ruled-in AMI patients of CK-MB (80–174 U/L) and CK-MB₂ (80–155 U/L). Coronary artery bypass patients (n = 24) and all trauma patients (n = 14) also demonstrated elevations in CK-MB and CK-MB₂, whereas only five of the trauma patients demonstrated increased CK-MB by IRMA. In patients (n = 7) having increased total CK and normal CK-MB by IRMA, the extraction assay for CK-MB and CK-MB₂ yielded increased values in all patients. This new approach to CK-MB and CK-MB₂ analysis can be performed within 30 minutes of sample receipt. J. Clin. Lab. Anal. 11:163–168, 1997. © 1997 Wiley-Liss. Inc.     

Creatine kinase and lactate dehydrogenase isoenzymes in serum and tissues of patients with stomach adenocarcinoma

Total activities of creatine kinase (EC 2.7.3.2; CK) and lactate dehydrogenase (EC 1.1.1.27; LD) and their isoenzymes were estimated in serum and tissue samples from patients with stomach adenocarcinomas who were to undergo gastric resection. Total CK activity (U/g protein) appeared to be markedly decreased in neoplastic stomach tissue. CK-BB was the predominant isoenzyme in both neoplastic and normal stomach tissues; however, the CK-BB/total CK ratio was increased in adenocarcinoma tissue. Macro CK type 1 was found in two neoplastic tissues and macro CK type 2 in 11. LD4 and LD5 isoenzymes were predominant in gastric tissues, but LD5 and the LD5/LD1 ratio were higher in adenocarcinoma tissue. At 24 h before surgery, CK-BB was demonstrated in sera of all patients and CK-MB in 69%. The CK-BB probably originated from neoplastic stomach tissue, which contains high CK activity, with BB isoenzyme predominating. After gastrectomy, CK and LD isoenzymes in sera were markedly increased by 24 h postsurgery. These alterations were attributed to release from damaged tissue during gastric resection.     

Macro creatine kinase type 1 with electrophoretic mobility identical to that of the MB isoenzyme

We describe the case of an elderly woman whose symptoms and electrocardiographic pattern initially suggested acute myocardial infarction. The value for total serum creatine kinase (EC 2.7.3.2; CK) was 737 U/L (reference interval: 22-269 U/L), and electrophoresis for CK isoenzymes demonstrated two bands, the more anodal migrating to the CK-MB region and the second migrating between the CK-MB and CK-MM regions. The above-normal total CK and electrophoretic pattern persisted during her 11-day hospital course. The QuiCK-MB (International Immunoassay Labs.) and Tandem-E CK-MB (Hybritech) immunoassays, however, showed CK-MB mass measurements within the normal range. In further investigation with a mixture of patient's serum and human-serum-based control containing all CK isoenzymes, the electrophoretic mobility of only CK-BB was altered, proving that the patient had antibody to the B unit of CK in her serum. Immunofixation revealed the more anodal band to be a CK-IgA lambda complex, and the more cathodal band, a CK-IgG kappa complex. Mixing the patient's serum with polyclonal antibody specific for CK-B slowed the electrophoretic mobility of only the more anodal band. Polyclonal antibody specific for CK-M had no effect on either band. Evidently, this patient had two different types of macro CK type 1, both containing CK-BB. We conclude that macro CK type 1 can mimic CK-MB and be a source of confusion.