Differential diagnosis of patients with abnormal serum creatine kinase isoenzymes

For the diagnosis of myocardial injury, particularly AMI, CK-MB has become the gold standard. Changing CK-MB activities in serially collected blood from patients with suggestive signs and symptoms of AMI is almost pathognomonic for infarction. Nevertheless, an increased CK-MB cannot be equated with AMI owing to the many other types of inflammatory, traumatic, and miscellaneous forms of injury to the heart and the trace activities of CK-MB in skeletal muscle. Other enzyme tests for AMI are less efficient. In order of decreasing efficiency, the tests are CK-MB, CK, LD1 greater than LD2 or LD1/LD2 greater than 0.76, AST and LD; the latter two tests are not cost effective and add little or nothing when results for CK-MB, CK, and LD isoenzymes are available. The value of the isoforms of CK-MM and CK-MB remains to be established. Early evidence suggests that they could be helpful in the diagnosis of AMI; however, owing to the greater technical difficulties in performing these tests, their use is necessarily more restricted. Enzyme testing on admission and then every 12 hours for 2 days is sufficient and effective in making the initial diagnosis. In patients presenting early after an attack, CK and CK-MB are often normal. Decisions on AMI cannot be made on blood tests collected in the emergency department. Clot-lysing agents like streptokinase, urokinase, and tPA have changed the therapy of AMI dramatically. Enzyme tests clearly separate patients with and without successful therapeutic or spontaneous reperfusion. With successful reperfusion, the uniform finding has been a "washout" phenomenon with significantly earlier peaking times for CK and CK-MB. The isoforms of CK and myoglobin give the earliest peaks after successful reperfusion. With faster turnaround times for these tests, they may become important tools in patient management.     

Serum isoforms of creatine kinase isoenzymes

The CK-2 and CK-3 isoenzymes of human serum creatine kinase (CK) can be further subdivided into five isoforms (subforms derived from the same isoenzyme). Three are derived from CK-3 and two from CK-2. The formation of these isoforms is a postsynthetic phenomenon brought about by a serum carboxypeptidase that acts on the M monomer of the enzyme. Sera from healthy subjects contain CK-3(1) as the dominant isoform with lesser amounts of CK-3(2) and CK-3(3). Following damage of muscle tissue, the serum isoform distribution changes as a result of the increased release of CK enzyme. This provides more diagnostic information concerning acute myocardial infarction and other muscle diseases than is available from routine CK isoenzyme analysis.     

Non-M CK--a practical measure of creatine kinase isoenzymes in cancer patients

The individual creatinine kinase (CK) isoenzymes CK-BB and CK-Macro II have previously been investigated as potential tumour markers. We believe there is a need for a system to measure those CK forms not usually present in serum. We have studied a CK-MB immunoinhibition kit which measures all residual CK activity following inactivation of M-subunit activity. In 162 patients with cancer we found no difference in grading (+ or -) between detailed isoenzyme studies and the simple non-M assay. In 33 samples with elevated non-M CK, detailed analysis showed BB alone (45%), Macro II alone (9%), or both (36%). Raised activities were mainly found in patients with small cell lung cancer (SCLC) (17/40; 43%) and GI Tumours (6/11; 55%). In patients with SCLC, elevated activities were associated with disseminated disease. Preliminary evidence indicates that Non-M CK may also be a simple means of monitoring initial treatment response.     

Spurious brain creatine kinase in serum from patients with renal disease.

Creatine kinase isoenzyme I(BB) is generally not detectable in normal serum, and its occurrence in serum has been documented in only a few disease states. In particular, increased activity of this isoenzyme has been reported in association with chronic renal failure, hemodialysis, and renal transplantation. The present study demonstrates that the apparent creatine kinase observed in the serum of such renal patients is an artifact, observed as a result of measuring creatine kinase isoenzymes by fluorescence. Our observations resemble those of McKenzie et al. [Clin. Chim. Acta 70, 333(1976)] concerning an artifact in the fluorometric determination of lactate dehydrogenase isoenzymes in the sera of patients with end-stage renal failure. The artifact binds to albumin, is not a protein, and occurs in some normal sera at very low concentrations. This artifact can be mistakenly identified as isoenzyme I in renal-disease patients if CK isoenzymes are determined fluorometrically.     

Cardiac troponin T and creatine kinase MB are not increased in exterior oblique muscle of patients with renal failure

BACKGROUND: Serum cardiac troponin T (cTnT) concentrations may be increased in patients with renal dysfunction without evidence of cardiac damage, as assessed by conventional methods. It has been suggested that these positive measurements result from the expression in skeletal muscle of fetal isoforms of cTnT, which are detected by the cTnT immunoassay. METHODS: Skeletal muscle (exterior oblique) biopsies were taken from healthy living kidney donors (n = 5) and transplant recipients (n = 19). The amounts of cTnT and creatine kinase (CK) isoenzymes in skeletal muscle of healthy controls were compared with those in patients with renal failure (Wilcoxon-Mann-Whitney test). cTnT was measured quantitatively by a second-generation assay, with a limit of detection of 1 microg/g of protein, and qualitatively by immunohistochemistry and immunoblotting. CK-MB was measured by quantitative electrophoresis. RESULTS: Minute quantities of cTnT were detected in 2 of the 5 (40%) control samples and 9 of the 19 (47%) renal failure samples, respectively, at mean concentrations of <5 microg/g of protein for both subject groups. This was <1/6000th that found in heart muscle. There was no significant difference in cTnT or CK-MB content in skeletal muscle between healthy controls and patients with renal failure. Increased serum cTnT did not predict detectable cTnT in skeletal muscle. cTnT was not detected qualitatively by immunoblotting or immunohistochemistry in any skeletal muscle samples. CONCLUSIONS: Uremia does not affect the content of cTnT or CK-MB in exterior oblique muscle, suggesting that cTnT detected in serum from patients with renal failure does not originate from skeletal muscle.     

Radioimmunoassay of creatine kinase isoenzymes in human serum: isoenzyme MM

Measurement of the mass concentration of serum enzymes by radioimmunoassay provides direct quantitation of specific isoenzymes and may be less subject to some of the limitations of traditional assay procedures for enzymes. We describe the development of a sensitive and specific radioimmunoassay for the muscle isoenzyme of creatine kinase, CM-MM, in human serum. CK-MM, purified from human skeletal muscle, was used to raise high-titer antisera and for iodination by the Chloramine T method. The radioimmunoassay required 50 microliter of sample, utilized a double-antibody separation method, and was completed in 24 h. Cross reactivity with CK-BB was virtually zero, 3--17% with CK-MB. The mass concentration of CK-MM in the serum of healthy subjects ranged from 36 to 1668 microgram/liter and correlated closely with total CK enzymatic activity. Serum concentrations of CK-MM from casually selected patients correlated less well with total CK enzymatic activity, suggesting the existence of other CK isoenzymes or the presence of inactive forms.     

Radioimmunoassay of creatine kinase isoenzymes in human serum: isoenzyme BB

We describe a sensitive, specific radioimmunoassay for the BB isoenzyme of creatine kinase (CK-BB) in serum. A sequential saturation assay was used to achieve sufficient sensitivity to detect the isoenzyme in 100-microliter serum samples of all healthy persons and patients tested. Bound and free antigen were separated by a second antibody system. Large excesses of purified isoenzyme MM did not react in the assay. Cross reactivity of two preparations of CK-MB was only 1 to 7+. The 95th percentile of serum CK-BB in 208 healthy adults was 6.2 microgram/liter. Within-assay and between-assay precision ranged from 5.5 to 11.9% and 9.7 to 13.6%, respectively.     

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.     

Stabilization of creatine kinase isoenzymes in the cerebrospinal fluid in cranio-cerebral trauma

Stabilization with dithiothreitol, together with optimization of Mg2+ and EDTA concentrations in the reaction mixture and storage of the CSF samples for 24 hrs at +4 degrees C, has been carried out for the first time to improve the sensitivity of the technique for measuring the activities of creatine kinase (CK) and its isozymes in the CSF of 38 patients during the first 24 hrs of craniocerebral injury. Dithiothreitol promoted mostly an increase of the CK-BB isozyme; the content of this isozyme in the cerebral tissue is rather high, and it is considered as the cerebral tissue marker. Generally stabilization augmented the CSF total CK activity by 2.2 times on an average (from 50.6 to 113.2 U/l), and the CK-BB activity by 3.5 times on an average (from 21.6 to 74.8 U/l). The method used in this work will help improve the diagnostic sensitivity of the CSF CK-BB measurements, this being significant for the detection of the cerebral tissue minute injuries after traumas and neurosurgery.     

胆红素脑病仔鼠血清肌酸激酶及其脑型同工酶的动态变化

目的:探讨胆红素脑病仔鼠血清肌酸激酶(creatinekinase,CK)及其脑型同工酶(creatinekinaseBB,CK-BB)水平的动态变化,为胆红素脑病早期诊断提供客观依据。方法:实验于2003-03/07在佳木斯大学实验动物中心完成,采用生后7日龄Wistar大鼠56只,平均体质量14.5g,雌雄各半。购自佳木斯大学实验动物中心。随机分为对照组和实验组,对照组8只,实验组48只。腹腔注射胆红素200mg/kg方法制备胆红素脑病模型,用酶动力法和琼脂糖凝胶电泳法对实验组和对照组注射胆红素后6,12,24,48,72,96h的血清CK及CK-BB水平进行动态观察。结果:胆红素脑病仔鼠血清中肌酸激酶12～24h明显升高,48h达峰值(52.46±34.76)μkat/L,对照组为(42.69±25.11)μkat/L;胆红素脑病仔鼠血清中CK-BB6h明显升高,48h达峰值(15.56±1.23)μkat/L,对照组为(8.52±0.54)μkat/L;且CK-BB升高的幅度较CK明显。结论:CK-BB可作为胆红素脑病的早期诊断指标,24～48h为取标本的适宜时间。     

Increased activities of creatine kinase and lactate dehydrogenase isoenzymes in a patient with metastatic ovarian tumor

A 50-year-old woman with metastatic rhabdomyosarcoma of the ovary had increased activities of creatine kinase (CK; EC 2.7.3.2), CK-MB isoenzyme, lactate dehydrogenase (LD; EC 1.1.1.27), and LD-2 isoenzyme in her serum. The isoenzyme activities did not show a pattern of increasing, then decreasing. Clinical findings, including electrocardiograms, did not support the diagnosis of myocardial infarction. We suggest that high activities of CK-MB and LD-2 in serum may serve as a marker of rhabdomyosarcoma.