Lactate dehydrogenase and creatine phosphokinase in serum - general information, principles of analytical methods, sources of errors, indications for analysis, biological material, reference ranges, interpretation of results.
LDH is most often measured to check for tissue damage. The enzyme LDH is in many body tissues, especially the heart, liver, kidney, skeletal muscle, brain, blood cells, and lungs. It is an oxidoreductase which catalyses the two-way transition of aerobic to anaerobic glycolysis (lactate - pyruvate).
The cell localization of LDH is in the cytoplasm. Its molecule is a tetramer, with two subunits heart type H (heart) in tissues with aerobic metabolism (myocardium, kidney, lung) and muscular type M (muscle) in tissues with anaerobic metabolism (skeletal muscles, liver, erythrocytes).
5 isoenzymes: LDH1 (HHHH), LDH2 (HHHM), LDH3 (HHMM), LDH4 (HMMM), LDH5 (MMMM).
Analytical methods for LDH: Total LDH is determined kinetically as the decrease of optic density within the UV spectrum is assayed (A at 340 nm/min). Isoenzymes in the heart muscle which possesses high H-subunit are measured kinetically with α-ketobutirate as a substrate and determines the activity of hydroxybutyrate dehydrogenase.
Source of error for LDH: false positive due to haemolysis
Indication for analysis LDH: Currently, the main use for LDH is as a general indicator of the existence and severity of acute or chronic tissue damage and, sometimes, as a monitor of progressive conditions such as some cancers, kidney disease, and liver disease.
Biological sample for LDH: blood is obtained under the standard conditions and serum without haemolysis is separated.
Reference range: LDH 230 – 460 U/l;
interpretation of results: Elevated levels of LDH
- Above 10x in advanced megaloblastic anaemia
- 5-10x in myocardial infraction, muscle injuries, acute pancreatitis
- Up to 5x in infectious mononucleosis, dyspeptic syndrome
Creatine phosphokinase catalyses the conversion of creatine and consumes ATP to create phosphocreatine and ADP causing the transfer of macroergic phosphate bond. The enzyme molecule is a dimmer. Cell localization in the cytoplasm and mitochondria of muscles, myocardial tissue, brain CK has 3 isoenzyme forms: CK-MM(muscle), CK-BB (brain) and CK-MB (heart)
Analytical method: 1. Three-Stage Kinetic, Absorption at 340 nm/min. 2. CK isoenzymes are determined semi-quantitatively by electrophoresis.
Source of error: False positive results in: mild muscle traumas; False negative results in: haemolysis; stale serum. The use of statin.
Indication for CK analysis: acute myocardial infarction, rhythm disorders, bundle branch block, patients with chest pain or if acute renal failure is suspected and muscle disorders
Biological sample: blood is obtained under the standard conditions and serum without haemolysis or hyperlipemia is separated.