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What is Lactate Dehydrogenase (LDH) test?

Lactate dehydrogenase or lactic acid dehydrogenase (LDH) is an enzyme or protein present in body. The main function of LDH is to produce energy in cells from glucose or sugar. LDH is present in various organs or tissues, including heart, muscles, liver, red blood cells (RBCs), lungs, kidneys, brain, pancreas and spleen. There are five types of this enzyme as mentioned below:

  • LDH1: Heart muscles and RBCs
  • LDH2: White blood cells (WBCs)
  • LDH3: Lungs
  • LDH4: Kidney, placenta and pancreas
  • LDH5: Liver and skeletal muscles

LDH is released in the blood when there is damage to cells or tissues in an organ. Hence, LDH test can identify tissue or cell damage in the body. However, it is a nonspecific test and is usually combined with other laboratory investigations to confirm the diagnosis. Measurement of different types of LDH enzymes mentioned above may identify the location of tissue damage, for eg raised LDH1 levels may indicate damage to heart cells, and an increase in LDH5 levels suggests liver diseases.

  1. Why is an LDH test performed?
  2. How do you prepare for an LDH test?
  3. How is an LDH test performed?
  4. What do LDH test results indicate?

An LDH test is performed to identify tissue or cellular damage in the body specifically to organs such as the heart (eg, heart attack or myocardial infarction), kidney, liver, skeletal muscles, brain or blood cells. If raised blood levels of LDH are observed, the doctor may order more specific investigations to confirm the location and severity of the problem.

LDH test is also used to monitor various conditions, such as liver diseases, kidney diseases, anaemia and certain cancers including blood cancer. This test is not considered very useful to diagnose a heart attack or myocardial infarction, as various other tests, such as troponin and creatine phosphokinase (CPK), are available, which provide more specific information on this condition than the LDH test.

LDH is a simple blood test. No special preparations or precautions are required for it. However, this test may be performed with other blood tests that may require special precautions such as fasting. A laboratory technician or healthcare provider should explain the procedure and requirement of this test to patients to make them comfortable before the test.

Certain medications may increase the levels of LDH in blood. These include anaesthetics, aspirin, clofibrate (for cholesterol), fluorides, pain medications, itraconazole (for fungal infection), narcotics, levodopa (for Parkinson’s disease) and procainamide. Intake of these medications may need to be stopped before an LDH test. Hence, it is useful to discuss with the doctor about any ongoing medications before this test.

LDH test is similar to other blood tests. Fasting is usually not required unless specified by the doctor. A healthcare professional or laboratory technician takes a blood sample from a vein most commonly from the arm or hand by inserting a sharp needle into it. About, 5-7 mL of blood is usually collected for performing this test. Mild pain or stinging sensations may be felt at the time of needle prick. Bleeding can be prevented by applying pressure at the site of needle prick using a cotton swab. It is important to inform the doctor if you notice any unusual signs or discomfort. The withdrawn blood sample is properly labelled and sent to a laboratory for analysis.

LDH in the blood is usually measured in international units per litre (IU/L).

Normal results: Normal levels of total LDH in the blood are 110-210 IU/L. Normal values of specific LDH fractions are provided below:

  • LDH1: 17-27%
  • LDH2: 28-38%
  • LDH3: 17-28%
  • LDH4: 5-15%
  • LDH5: 5-15%

Normal levels of blood LDH may indicate that the body organs, in which LDH is usually present, are functioning properly and there is no evidence of tissue damage.

Abnormal results: LDH levels usually rise when there is tissue or cell damage in certain organs.

It may be a sign of some of the  following conditions:

Decreased levels of LDH are generally not considered harmful. The doctor may recommend additional tests or investigations to diagnose the underlying condition.

Since high LDH indicates the presence of certain types of cancer, reduction in LDH levels in such patients could be a sign of efficiency of treatment.

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational perspective and is in no way a substitute for medical advice from a qualified doctor.

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  1. National Health Service [internet]. UK; Lactate dehydrogenase (LDH) test
  2. Carty RP, Pincus MR, Sarafraz-Yazdi E. Clinical enzymology. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 23rd edition. 2017
  3. Hernecky CC, Berger BJ. Lactate dehydrogenase (LD) isoenzymes. In: Chernecky CC, Berger BJ, eds. Laboratory Tests and Diagnostic Procedures. 6th edition. 2013 pp 702-703
  4. Frances T Fischbach. A Manual of Laboratory and Diagnostic Tests. Chapter on Lactate Dehydrogenase (LD, LDH). 7th Edition. 2003.
  5. University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; Lactic Acid Dehydrogenase (Blood)