LDH Blood Test: Levels, Ranges, and What Results Mean

What is LDH (Lactate Dehydrogenase)?

I often see patients in my clinic who are puzzled by their LDH results. Lactate dehydrogenase is an enzyme found in nearly every cell in your body, with the highest concentrations in the heart, liver, kidneys, skeletal muscles, and red blood cells. Its job is to help convert lactate to pyruvate during energy metabolism. When cells are damaged or stressed, LDH leaks into the bloodstream, making it a useful marker of tissue injury.

Why is the LDH Test Ordered?

In my practice, I typically request an LDH test when I suspect tissue damage from conditions such as heart attack, liver disease, muscle injury, or hemolytic anaemia. It's also used to monitor the progression of certain cancers and the effectiveness of chemotherapy. LDH levels can rise in many different disorders, so it is not a specific diagnostic test but rather a helpful clue that prompts further investigation.

Normal LDH Reference Ranges by Age and Gender

Reference ranges can vary slightly between laboratories, but the following table provides typical values (in U/L) for adults and children. Women sometimes have slightly lower levels than men, but the difference is rarely significant in clinical practice.

These values are intended as a guide. Always interpret your results with your doctor, who will consider your overall health and other test findings.

What Does a High LDH Level Mean?

Elevated LDH is a sign that some cells in the body are damaged or under stress. Common causes include:

• Heart attack (myocardial infarction): LDH rises within 24–48 hours and can remain high for several days.
• Liver disease: Hepatitis, cirrhosis, or liver injury (e.g., from alcohol or drugs) can elevate LDH.
• Lung injury: Pulmonary embolism or pneumonia may cause increased LDH.
• Muscle trauma: Severe exercise, rhabdomyolysis, or muscle crush injury.
• Haemolytic anaemia: Rapid breakdown of red blood cells releases LDH.
• Cancers: Many solid tumours and leukaemias produce high LDH, often used as a tumour marker.

Is High LDH Dangerous?

A single high LDH value does not always mean a serious problem. I have seen patients with high LDH from intense physical training or a mild viral illness. However, persistently or very high levels (above 500 U/L) warrant prompt evaluation. In critical illnesses such as sepsis or acute liver failure, rising LDH can indicate worsening tissue damage and a poorer prognosis.

What Does a Low LDH Level Mean?

Low LDH is less common and usually not a cause for concern. Slightly low levels can occur in people who are very physically fit or those with certain genetic conditions. There is no widely recognised disease linked exclusively to low LDH, so I rarely focus on low values unless they are extreme.

LDH During Pregnancy

Pregnancy causes normal changes in blood volume and organ function. LDH levels often remain within the normal range, but mild increases can occur in the third trimester due to the increased metabolic demands on the liver and placenta. However, a sudden rise in LDH late in pregnancy may be a red flag for pre-eclampsia or HELLP syndrome (haemolysis, elevated liver enzymes, low platelets). My patients who develop headache, right upper abdominal pain, or visual changes along with high LDH need immediate medical attention.

Can LDH Help Monitor Cancer Treatment?

Yes. Many oncologists use LDH as a simple, cost-effective marker to track certain cancers, especially lymphoma, leukaemia, and testicular cancer. A rising LDH after treatment may suggest recurrence or resistance, while a decreasing level often indicates a good response. In my experience, LDH is not a standalone test but adds valuable information when combined with imaging and other biomarkers.

Factors That Can Affect LDH Levels

Several factors can cause temporary fluctuations in LDH, which is why I always ask patients about their recent activities. These include:

• Intense exercise within 24–48 hours before the blood draw
• Recent surgery or trauma
• Haemolysis of the blood sample itself (if the specimen was handled improperly)
• Certain medications, such as statins or some antibiotics
• Alcohol consumption

How to Prepare for an LDH Test

No special preparation is needed for a standard LDH blood test. I usually recommend avoiding strenuous exercise and alcohol for at least 24 hours prior, as these can skew results. The test is simple — a small blood sample from your arm — and results are typically available within a day.

If you have any concerns about your LDH level, don't hesitate to discuss them with your doctor. Knowledge is power, and understanding what this enzyme tells us about your body can lead to earlier diagnosis and better outcomes.