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Lactate dehydrogenase LD, LDH 

Lactate dehydrogenase LD, LDH

Definition:

– LDH is an enzyme reversibly catalyze the oxidation of lactate to pyruvate by transferring hydrogen ion from lactate to the cofactor NAD+ as follow:

Lactate + NAD+ =====>>  pyruvate  + NADH + H+

– LDH is an intracellular enzyme found in almost all body tissues that is released after tissue damage.

– The highest concentrations are found in: heart, liver, kidneys, RBCs, and skeletal muscle cells.

– The elevation of LDH values due to tissue damage like trauma, ischemia, or acid/base imbalance.

– Can’t pinpoint the specific location damage so LDH Isoenzyme should be performed to narrow down the source of tissue damage.

– LDH is composed of 4 subunits distributed as follow:-

LD1 (HHHH), LD2 (MHHH), LD3 (MMHH), LD4 (MMMH), LD5 (MMMM) They can Performed electrophoritically.

Clinical significance:

– Total LDH Increased in : Megalobalastic and pernicious anemia, carcinoma, viral hepatitis, cirrhosis, obstructive jaundice, renal diseases, skeleton muscular diseases, CHF, MI, leukemia, hemolytic anemias, sickle cell anemia, lymphoma, renal infarction, acute pancreatitis.

-Decreased in : genetic deficiency of H or M subunits, Irradiation therapy.

– Increased LD1 in : AMI, hemolytic anemia, germ cell tumors, renal infarct, invivo or invitro hemolysis and muscular injury.

-Increased LD2 in : masculardystrophy, pernicious anemia, renal infarction and tumors.

-Increased LD3 in : pulmonary embolism, malignancy, splenic necrosis.

– Increased LD4 in : hepatitis, lymphoma, platelets destruction.

– Increased LD5 in : Arthritis, skeletal muscle infection, septic shock.

Methodology:

Kinetic/ Pyruvate to lactate.

Normal range:

Serum        225-480   U/L

18-33%          LD1

28-40%          LD2

18-30%          LD3

6-16%            LD4

2-13%            LD5

<20 U/L         CSF

Limitation:

– the pyruvate to lactate reaction is preferred on theoretical grounds, since the equilibrium constant is so large, but this method has disadvantage due to earlier loss of linearity.

– LD6 has been described when prognosis is poor and may released from liver LDH not specific test when elevated so it need more another tests to diagnose disease and to limit the origin of it.

LDH Isoenzyme is useful in diagnosis of MI, liver diseases, tumors and pulmonary embolism. –

– Some drugs cause elevation of serum level such as: heparin, anesthetic agents, cephalosporin, interferon,& valporic acid.

Lactate dehydrogenase LD, LDH

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