Lactate Dehydrogenase (LDH) Isoenzyme Activity in Serum/Plasma (Total LDH Activity)
This test measures the total activity of the enzyme lactate dehydrogenase (LDH), which plays a role in energy production in cells. LDH levels can help identify conditions affecting muscle, liver, heart, or red blood cells.
["LDH helps diagnose and monitor conditions linked to tissue damage or metabolic stress."]
Key facts at a glance
- LOINC
- 51518-9
- Short code
- LDH4 CFr Plr Elph
- Synonyms
- LDH4 CFr Plr Elph
- Category
- chemistry
- Sample
- fluid
- Container
- Sterile tube
- Units
- N/A
- Ref low
- 140
- Ref high
- 280
- Critical range
- 7.2 N/A – 7.6 N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- electrophoresis
- CPT
- 83615
- Specimen volume
- 2-5 mL
- Stability
- Room temperature: 2h, Refrigerated: 24h
- Hemolysis max
- 300
- TAT
- 4–24 hours
- Order
- routine
What Is Lactate Dehydrogenase (LDH)?
Lactate dehydrogenase (LDH) is an enzyme found in many tissues, including the heart, liver, muscles, and red blood cells. It helps convert lactate into pyruvate, a process essential for energy production. When cells are damaged, LDH can leak into the bloodstream, raising its levels. This test measures the total activity of LDH in your blood.
Why Is This Test Ordered?
Doctors may order a total LDH test to investigate symptoms like fatigue, muscle pain, chest discomfort, or unexplained bruising. It can also help diagnose or monitor conditions such as heart attacks, liver disease, anemia, or certain cancers.
Common Conditions Affecting LDH Levels
Elevated LDH levels may suggest conditions like myocardial infarction (heart attack), liver disease (e.g., hepatitis), muscle disorders, hemolytic anemia (red blood cell destruction), or certain cancers. Lower levels are less commonly noted but may occur in rare cases of severe muscle wasting or specific genetic disorders.
What to Expect Before the Test
No special preparation is usually needed, but you may be asked to fast for a few hours if your blood is drawn early in the morning. Avoid strenuous exercise or consuming alcohol for 24 hours before the test, as these can temporarily affect LDH levels.
Reference range
Adult: 140-280 U/LN/A
No special preparation required. Inform provider of any chest pain or symptoms.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Clinical Significance of LDH Levels
Short name
Total LDH Activity
Frequently asked questions
How Long Does It Take to Get Results?
Can Diet or Exercise Affect LDH Levels?
Is There Any Risk or Discomfort with This Test?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy