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Creatine kinase { CK, CPK }
Creatine kinase { CK, CPK }
Definition :
– CK is an enzyme catalyzes the reversible transfer of phosphate from ATP to creatine. This reaction makes possible the storage of high- energy phosphate in more stable from than in ATP .
– CK is present in high concentration in skeletal & cardiac muscle and lower in liver, kidney , lungs, and brain.
– By performing CK Isoenzyme, we can determine the origin of CK,
it make up of 2 subumits, M and B which will form 3 isoenzymes :
-CK1 { CK – BB} present in brain, gastrointestinal and genitourinary tract.
-CK2 { CK-MB} present in heart.
– CK3 { CK-MM} present in skeletal muscle.
– Total CK rise after AMI 2-6 hours, reach peak 18-36 hors and return to baseline 3-6 days after onset of damage CK – MB rise after AMI 4-8 hours, reach 18-24 hours, and return to normal 3 days later.
Clinical significance:
– Increased total CK1,BB in : head injury, after neurosurgery, subarchnoid hemorrhage, and labor .
-Increased CK2,MB in : MI angina pectoris, cardiac sugery, AMI .
– Increased CK3, MM in : muscle disorders,
-Most conditions described under total CK .
– Decreased Total CK: have no meaning but reflect small muscle mass Specimen and collection .
Methodology :-
Kinetic /NAC.
Normal range:-
30-200 U/L
CK1 absent or rare.
CK2 < 4-6% of total CK.
CK3 > 94-96% of total CK.
Limitation :-
many drugs cause elevation in serum CK level include captopril, lithium, carbon monoxide, cocaine, and MI injection.
CK-MB mass assay:-
– It measures the protein concentration of CK-MB rather than its catalytic activity.
-Immunoassay techniques using monoclonal antibodies.
– It is more sensitive and has fewer interferences.
– Mass assays can detect an increased serum concentration of CK-MB about 1 h earlier
– Mass assays can detect an increased serum concentration of CK-MB about 1 h earlier
– A normal CK-MB mass concentrations over a period of 6-8 h have a negative predictive value of 97%.
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