[Creatine kinase isoenzymes: idiopathic occurrence of creatine kinase BB activities in patient serum (author's transl)]

Serum creatine kinase (CK) activity after M-subunit inhibition in patients with atypical CK isoenzymes--a comparison to findings in acute myocardial infarction

The serum levels of total creatine kinase (CK), and of CK-B, as estimated by the enzymatic anti-M-subunit immunoinhibition method, were studied in 14 patients with CK-B elevation associated with advanced malignant disease, in nine subjects with electrophoretically verified, immunoglobulin-bound CK-BB (macro CK) and in 28 patients with acute myocardial infarction (AMI). The range of CK-B activity was similar in all three groups. In AMI, the ratio CK-B/total CK at peak CK-B was less than 13% (mean 7%). In both the groups with atypical CK, the ratios varied from about 30% to nearly 100%, with a mean amounting to 2/3 of total CK activity. CK-B elevations in patients with untreated malignant tumours tended to increase with time, but occasionally remained fairly constant for months, like those in subjects with macro CK. Complementary CK isoenzyme separation, e.g. by electrophoresis, is needed to differentiate conditions with atypical CK activity, detected by routine use of CK-B determinations in the diagnosis of AMI.

[Variant creatine kinase isoenzymes: frequency and clinical significance (author's transl)]

To estimate the incidence of variant creatine kinase (CK)isoenzymes, 1,191 unselected patients were screened by means of CK:CK - MB ratio. When CK - MB was higher than 20% of the total CK in the immunoinhibition test, and a myocardial infarction could be excluded, a CK-isoenzyme electrophoresis was performed. We found macro-CK-BB-emia in 13 patients, but only three of them had elevated total CK activity. All patients but two were at the typical age of over 60 years; two males were 2 and 9 years old. The clinical diagnosis in macro-CK-BB-emia was predominantly cardiocerebrovascular insufficiency due to arteriosclerosis. In 16 other patients, the presence of an isoenzyme migrating cathodically to CK-MM was found. In this group, a malignant metastatic tumor was found in eight cases, the rest predominantly suffered from severe liver disease. Presence of both variant CK isoenzymes may lead to diagnostic or therapeutic errors due to the altered CK:CK-MB ratio. According to our studies, a variant CK isoenzyme occurs in 2.6% of hospitalized patients, but this will lead to problems diagnosing acute myocardial infarction only in the group with elevated total CK (0.42% of our patients).

Stability of macro creatine kinases and creatine kinase isoenzymes compared: heat inactivation test for determination of thermostable creatine kinases

Creatine kinase isoenzymes showed decreasing thermal stability and increasing lability towards pH changes in the order: MM, MB, and BB. The three isoenzymes exhibited their highest stability between pH 6.5 and 7.0. At 37 degrees C and an almost physiological pH of 7.5 the decay constants were 0.025, 0.164 and 0.580 h-1 (MM, MB, and BB isoenzyme), respectively. In contrast to free creatine kinase BB, immunoglobulin-linked creatine kinase BB (macro creatine kinase BB, type 1 macro creatine kinase) showed a markedly higher stability; this accounts for the persistence of creatine kinase BB activity in macro creatine kinasaemia. In addition we identified a second type of macro creatine kinase in patients' sera, which is also thermostable. A simple heat inactivation test (20 minutes, 45 degrees C, immunoinhibition of the M-subunits) differentiates thermostable macro creatine kinases from thermolabile creatine kinases and thus completes isoenzyme diagnosis.

Macro-creatine kinase-BB: observations on 6 patients

From 2000 sera with elevated total creatine kinase (EC 2.7.3.2) activity the sera of 6 patient showed a persistent high and anamnestically inexplicable creatine kinase activity level. The serum isoenzyme pattern was analyzed by four different methods. Electrophoresis revealed an atypical creatine activity band located between creatine kinase-MM and creatine kinase-MB. An adequate estimation of the persistent enzyme activity could only be achieved by immunotitration (immunoprecipitation), which identified the creatine kinase activity as due primarily to the isoenzyme creatine kinase-BB. Other methods (immunoinhibition and column chromatography) may lead to misinterpretations. The atypical serum creatine kinase-BB showed a higher molecular weight (Mr = 250,000) and altered substrate affinity as compared to native creatine kinase-BB. Both properties are attributable to the binding of creatine kinase-BB to immunoglobulins.

Atypical serum creatine kinase isoenzyme pattern caused by complexing of creatine kinase-BB with immunoglobulins G and A1),2)

12 cases are described, which show high serum creatine kinase-BB levels, as well as atypical creatine kinase activity band located between normally migrating creatine kinase-MM and creatine kinase-MB. It is shown that the altered properties of the serum creatine kinase-BB, namely its molecular size, heat resistance, electrophoretic mobility, but not its immunological behavior, are caused by complexing with kappa-chains of immunoglobulins G or A. The complex occurring in vivo could also be produced in vitro by using purified patients' IgG and human creatine kinase-BB.

[Macro-creatine kinase; circulating immunoglobulin enzyme complexes as cause of elevated CK-activities (author's transl)]

We report a case of a woman (58 years old) with persistent and elevated CK activities and without corresponding clinical signs. For seven months CK-B activity was determined above normal by an inhibition test. By exclusion chromatography, ion-exchange chromatography, electrophoresis of CK isoenzymes and immunological methods we were able to explain this phenomenon as Macro CK consisting of immunoglobulin G bound CK-BB.

Differential diagnosis importance of the creatine kinase isoenzyme pattern in delirium tremens

Total CK and CK-MB (by the inhibition test, Merck-1-CK-MB) were measured in 33 patients which had to be admitted to the department of psychiatry due to acute withdrawal symptoms (predelirium, delirium) caused by chronic alcohol abuse. The results were evaluated together with the routinely performed laboratory determinations as well as clinical examination and morphologic investigations (ECG, X-ray examination of the thorax, EEG, CT). The results show that the CK-MB/total CK relationship represents also in these patients the most reliable parameter to discriminate elevated total CK values. In no but one case a substantial CK-BB release from the central nervous system could be demonstrated by the inhibition test. In 83% of the patients with elevated total CK activities it was possible to exclude an affection of the heart muscle (CK-MB portion below 6%). The CK-MB/total CK-quotient was clearly superior to the total CK/GOT relationship, by which a myocardial affection could be excluded in less than 40%. In four patients the CK-MB portion was above the critical decision limit of 6%: three obtained between 6% and 7%, one even 17%. The results suggest that the CK-MB/total CK-quotient may represent the most sensitive and reliable parameter of myocardial affection in patients with an alcohol intoxication and/or a delirium tremens.

Serum creatine kinase BB linked to immunoglobulin G

We describe an atypical form of creatine kinase in the serum of a woman after myocardial infarction. Electrophoresis on agarose gel showed a single fraction between CK-MM and CK-MB isoenzymes. After ion-exchange chromatography on DEAE-Sephadex A-50 we isolated the atypical CK and CK-BB as detected by electrophoresis of the eluted fractions. Results of our immunological investigations and exclusion chromatography clearly demonstrate that the atypical CK consists of complexes with high molecular masses formed by CK-BB isoenzyme and immunoglobulin G. The clinical significance, if any, of this Macro CK has yet to be determined.

Aids to the evaluation of diagnostic performance, as applied to immunological creatine kinase-MB assay in myocardial infarction

Immunoassay of creatine kinase-MB provides numerical information, which makes it possible to estimate quantitatively the diagnostic performance following myocardial infarction. Two graphical methods for such an evaluation are presented. The relationship between technical sensitivity and specificity was analyzed using a continuous function, the receiver-operator characteristic curve. Using this function, a diagnostic threshold ("upper normal limit") was chosen, which balances both technical specificity and sensitivity on the first day following infarction. On the second and third days this threshold caused a progressive loss of technical sensitivity. The relationship between effectiveness and the prevalence of myocardial infarction in the tested population was evaluated with a nomogram correlating these two quantities. With the chosen diagnostic threshold, effectiveness is independent of prevalence on the first day, but the loss in technical sensitivity on subsequent days causes effectiveness to decay when the prevalence is high.