Lactate Dehydrogenase Isoenzymes Blood Test

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Lactate Dehydrogenase Isoenzymes Blood Test

$58.00 AUD

Had an elevated total LDH result and want to work out which tissue (heart, liver, muscle, lungs, or red blood cells) is the likely source?

Separates total LDH into five tissue-specific fractions to identify the source of an elevated LDH result. Fractions relate to heart and red blood cells (LDH-1/2), lungs and lymphocytes (LDH-3), and liver and skeletal muscle (LDH-4/5).

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Overview

LDH isoenzyme testing takes the information from a total LDH result one step further by separating the enzyme into five distinct fractions. Each fraction corresponds to different tissue sources, which helps narrow down where in the body cell damage may be occurring.

The five isoenzymes are LDH-1 through LDH-5. LDH-1 and LDH-2 are concentrated in the heart and red blood cells. LDH-3 is found predominantly in the lungs and lymphocytes. LDH-4 and LDH-5 are associated with the liver and skeletal muscle. The pattern of elevation across these fractions gives your practitioner a more specific guide to the likely source of an elevated total LDH.

Historically, a "flipped" LDH ratio (where LDH-1 exceeds LDH-2) was used to support the diagnosis of myocardial infarction. Cardiac troponin tests have largely replaced this application due to their far greater sensitivity and specificity for heart muscle damage. LDH isoenzymes remain clinically relevant in haematology, particularly for confirming haemolytic conditions where LDH-1 and LDH-2 are elevated alongside low haptoglobin and elevated reticulocytes.

In oncology, LDH isoenzymes are used to monitor disease activity in lymphoma, germ cell tumours, and other malignancies. Elevated LDH-5 in the setting of suspected liver or muscle disease supports further targeted investigation of those organs.

This is a follow-up test, not a first-line screen. It is ordered when total LDH is elevated and the source is unclear, or when the clinical context requires more specific tissue attribution. Your practitioner will interpret the isoenzyme pattern alongside imaging, other blood tests, and your symptoms.

Symptoms

To determine the tissue origin of an elevated total LDH, providing a more specific guide to diagnosis when the cause of LDH elevation is unclear.

Questions

  • Cardiac troponin I and T are far more sensitive and specific markers of heart muscle damage and have replaced LDH isoenzymes for acute cardiac diagnosis. LDH isoenzymes are now used primarily for haematological conditions, cancer monitoring, and non-cardiac causes of elevated LDH.
  • Many cancers can raise LDH, including lymphoma, leukaemia, germ cell tumours (testicular cancer), melanoma, and metastatic solid tumours. LDH is used as a prognostic marker in staging some of these cancers.
  • Yes. Red blood cells contain high concentrations of LDH. If the blood sample haemolyses (red cells break down) during collection or transport, LDH levels will be falsely elevated, particularly LDH-1 and LDH-2. Careful sample handling is essential.
  • Elevated LDH-5 is most commonly associated with liver disease (hepatitis, cirrhosis) or skeletal muscle damage (myopathy, rhabdomyolysis). Exercise can also transiently raise LDH-5.
  • Yes. Haemolytic anaemia causes elevated LDH-1 and LDH-2 as red blood cells are destroyed. The isoenzyme pattern can help confirm a haemolytic process alongside other markers such as haptoglobin and reticulocyte count.

Dr. Vu Tran
Bloody Good’s Chief Medical Officer

2 Biomarkers Tested

How to prepare

Fasting is not required. Avoid strenuous exercise for at least 24 hours before the test, as vigorous muscle activity releases LDH from muscle cells and can distort results. Haemolysis (breakdown of red blood cells in the sample) also artificially elevates LDH, so the sample requires careful collection.

After the test

Your doctor will interpret the isoenzyme pattern alongside the clinical picture, other blood tests, and imaging. In oncology settings, total LDH and isoenzymes are used as disease activity markers. Discuss the pattern and its implications with your treating physician.

Your test results will be available in your private dashboard. If there are any urgent issues, we'll let you know so you can follow up with your health professional.

Understanding results

The laboratory reports each isoenzyme fraction as a percentage of total LDH. An elevated LDH-1 (flipped ratio: LDH-1 greater than LDH-2) was historically used to help diagnose myocardial infarction, though cardiac troponin tests have largely replaced this role. Elevated LDH-4 and LDH-5 points toward liver or muscle disease. Elevated LDH-3 may indicate lung disease or haematological malignancy. LDH isoenzymes are still used in oncology (particularly in lymphoma and germ cell tumour monitoring) and in haematology for haemolytic conditions.

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Frequently Asked Questions

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If your test needs fasting, we’ll include that in your instructions after you order. Fasting usually means no food for 8–12 hours, but water is fine.

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