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Information About

Lactate Dehydrogenase





ENZYME ISOFORMS


Usually LDH-2 is the predominant form in the serum. An LDH-1 level higher than the LDH-2 level (a "flipped pattern"), suggests Myocardial Infarction (damage to heart tissues releases heart LDH, which is rich in LDH-1, into the bloodstream). The use of this pheonomenon to diagnose infarction has been largely superseded by the use of Troponin I or T measurement.


GENETICS IN HUMANS

The M and H subunits are encoded by two different Gene s:
  • The M subunit is encoded by ''LDHA'', located on Chromosome 11p15.4 ()

  • The H subunit is encoded by ''LDHB'', located on chromosome 12p12.2-p12.1 ()


Mutations of the M subunit have been linked to the rare disease ''exertional myoglobinuria'' (see OMIM article), and mutations of the H subunit have been described but do not appear to lead to disease.


MEDICAL USE


Hemolysis

In Medicine , LDH is often used as a marker of tissue breakdown. As LDH is abundant in Red Blood Cell s and can function as a marker for Hemolysis . A blood sample that has been handled incorrectly can show false-positively high levels of LDH due to Erythrocyte damage. It can also be used as a marker of Myocardial Infarction .


Tissue turnover

Other uses are assessment of Tissue Breakdown in general; this is possible when there are no other indicators of Hemolysis . It is used to follow-up Cancer (especially Lymphoma ) patients, as Cancer Cell s have a high rate of turnover, with destroyed cells leading to an elevated LDH activity.


Exudates and transudates

Measuring LDH in fluid aspirated from a Pleural Effusion (or Pericardial Effusion ) can help in the distinction between Exudate s (actively secreted fluid, e.g. due to Inflammation ) or Transudate s (passively secreted fluid, due to a high Hydrostatic Pressure or a low Oncotic Pressure ). LDH is elevated (>200 U/l) in an exsudate and low in a transudate. In Empyema , the LDH levels generally will exceed 1000 U/l.


Meningitis and encephalitis

The Enzyme is also found in Cerebrospinal Fluid where high levels of lactate dehydrogenase in cerebrospinal fluid are often associated with Bacteria l Meningitis . High levels of the enzyme can also be found in cases of Viral meningitis, generally indicating the presence of Encephalitis and poor Prognosis .