Lactate Dehydrogenase (LDH) Blood Test: Normal Ranges, Causes & What Your Results Mean

What Is Lactate Dehydrogenase (LDH)?

Lactate dehydrogenase (LDH) is an enzyme found in nearly all living cells throughout the body. It plays a important role in energy production by catalysing the conversion of lactate to pyruvate (and vice versa) during the metabolic process of glycolysis. Because LDH is present in such a wide variety of tissues, including the heart, liver, kidneys, lungs, muscles, blood cells, and brain, it serves as a general marker of tissue damage or cell death.

When cells are damaged or destroyed, LDH is released into the bloodstream, causing serum levels to rise. This makes LDH a sensitive but non-specific marker - it indicates that tissue damage has occurred somewhere in the body, but does not pinpoint the exact location without additional testing.

LDH exists in five different forms called isoenzymes (LDH-1 through LDH-5), each predominating in different tissues:

• LDH-1: Heart and red blood cells
• LDH-2: White blood cells and reticuloendothelial system
• LDH-3: Lungs and other tissues
• LDH-4: Kidneys, placenta, and pancreas
• LDH-5: Liver and skeletal muscle

While isoenzyme analysis can help localise the source of tissue damage, it is rarely performed in routine UK clinical practice today. Instead, LDH is typically used in combination with other more specific markers to narrow down the clinical picture.

Why Is LDH Tested?

LDH testing is requested in a variety of clinical contexts:

• Cancer monitoring: LDH is used as a tumour marker in several cancers, particularly lymphomas, testicular cancer, and melanoma. Elevated LDH in these conditions often indicates a higher tumour burden, more advanced disease stage, or poorer prognosis. In non-Hodgkin lymphoma, LDH is a component of the International Prognostic Index (IPI).
• Haemolytic anaemia: When red blood cells are destroyed prematurely (haemolysis), they release their LDH (predominantly LDH-1 and LDH-2) into the blood. LDH is one of the key markers used alongside haptoglobin, bilirubin, and reticulocyte count to diagnose and monitor haemolytic anaemia.
• Tissue damage assessment: LDH can be elevated following heart attacks (myocardial infarction), pulmonary embolism, liver injury, kidney damage, and muscle breakdown (rhabdomyolysis), though more specific markers are now preferred for many of these conditions.
• Treatment response monitoring: In patients with cancer or haematological conditions, serial LDH measurements help assess response to chemotherapy or other treatments. A declining LDH suggests the tumour is responding; a rising LDH may indicate disease progression.
• Infectious disease: Markedly elevated LDH can accompany severe infections, including Pneumocystis jirovecii pneumonia (PCP) in immunocompromised patients, COVID-19, and other serious pulmonary infections.
• Pleural and peritoneal fluid analysis: LDH measurement in fluid samples helps distinguish between exudative (inflammatory) and transudative (non-inflammatory) effusions using Light's criteria.
• Megaloblastic anaemia: In vitamin B12 or folate deficiency, ineffective erythropoiesis in the bone marrow causes intramedullary red cell destruction, releasing LDH and producing very high serum levels.

Normal Ranges

LDH is measured in units per litre (U/L). Reference ranges vary slightly between laboratories depending on the method and temperature used for the assay.

Age Group	Normal Range (U/L)	Notes
Adults (18+)	120 – 246	Some labs use 135-225 or 140-280
Children (2-17 years)	120 – 300	Higher upper limit in growing children
Infants (0-2 years)	160 – 450	Highest normal range; declines with age

Key interpretation points:

• Always compare your result to the specific reference range on your laboratory report, as ranges vary between different assay methods.
• Mild elevations (1-2x the upper limit) are often non-specific and may result from strenuous exercise, sample haemolysis (a laboratory artefact), or minor tissue injury.
• Moderate elevations (2-5x) suggest significant tissue damage and warrant clinical investigation.
• Marked elevations (more than 5x) are seen in severe haemolysis, megaloblastic anaemia, advanced cancer, or serious organ damage.
• LDH can be falsely elevated if the blood sample has been mishandled (haemolysed during collection or processing). If an unexpectedly high result is obtained, a repeat sample may be requested.

What Do High LDH Levels Mean?

Elevated LDH indicates that cells somewhere in the body have been damaged or destroyed. Common causes include:

• Haemolytic anaemia: Autoimmune haemolytic anaemia, sickle cell disease, thalassaemia, thrombotic thrombocytopenic purpura (TTP), haemolytic uraemic syndrome (HUS), and mechanical heart valve haemolysis all cause elevated LDH through red blood cell destruction.
• Megaloblastic anaemia: Vitamin B12 or folate deficiency causes ineffective erythropoiesis, leading to very high LDH levels - sometimes exceeding 1,000 U/L. Treatment with the deficient vitamin rapidly normalises LDH.
• Lymphoma and leukaemia: LDH is a well-established prognostic marker in non-Hodgkin lymphoma, Hodgkin lymphoma, and acute leukaemia. Higher levels correlate with greater tumour burden and more aggressive disease.
• Testicular cancer: LDH is one of three serum tumour markers (alongside AFP and beta-hCG) used in the staging and monitoring of testicular germ cell tumours.
• Liver disease: Hepatitis, cirrhosis, and liver damage from any cause can elevate LDH (predominantly LDH-5). However, more specific liver enzymes (ALT, AST) are preferred for liver disease assessment.
• Myocardial infarction: LDH rises after heart muscle damage, though troponin has largely replaced LDH for cardiac diagnosis due to its far superior specificity.
• Pulmonary embolism: LDH may be elevated following significant pulmonary embolism due to lung tissue damage.
• Strenuous exercise: Intense physical activity, particularly eccentric exercise (such as downhill running or heavy weight training), causes temporary muscle cell damage and LDH elevation that resolves within 24-72 hours.

What Do Low LDH Levels Mean?

Low LDH levels are uncommon and rarely clinically significant, but they can occur in certain circumstances:

• Normal finding: A low-normal LDH is generally a reassuring result, indicating no significant tissue damage or cell turnover.
• Genetic LDH deficiency: Rare inherited mutations can cause reduced LDH production. LDH-A deficiency (affecting LDH-5, predominantly in muscle) can cause exertional myoglobinuria (dark urine after exercise) due to impaired anaerobic glycolysis. LDH-B deficiency is usually asymptomatic.
• High dose vitamin C intake: Very high doses of ascorbic acid (vitamin C) have been reported to interfere with some LDH assays, producing falsely low results.
• Oxalate interference: High levels of oxalate in the blood can inhibit LDH enzyme activity in vitro.
• Effective treatment response: In patients being monitored for cancer or haemolytic conditions, declining LDH levels towards or below normal represent a positive treatment response.

How to Improve Your LDH Levels

Because LDH is a marker of tissue damage rather than a modifiable health parameter in itself, "improving" LDH means addressing the underlying cause of elevation:

If LDH Is Elevated Due to Haemolysis or Blood Disorders

• Treat the underlying condition: Autoimmune haemolytic anaemia may require corticosteroids or immunosuppressive therapy. Sickle cell disease and thalassaemia require specialist haematological management. TTP is a medical emergency requiring plasma exchange.
• Correct nutritional deficiencies: If megaloblastic anaemia is the cause, vitamin B12 injections or high-dose oral folate rapidly restore normal blood cell production and normalise LDH.

If LDH Is Elevated Due to Cancer

• Cancer treatment: Chemotherapy, immunotherapy, radiotherapy, or surgery, as appropriate for the specific cancer type, should lead to declining LDH if the treatment is effective.
• Regular monitoring: Serial LDH measurements help your oncologist track treatment response and detect early relapse.

General Health Measures

• Allow recovery after exercise: If strenuous exercise has caused a temporary LDH rise, adequate rest and recovery (including proper nutrition, hydration, and sleep) allows levels to normalise within 2-3 days.
• Protect your liver: Limit alcohol consumption to within NHS guidelines (14 units per week), maintain a healthy weight, and avoid hepatotoxic substances to minimise liver-related LDH elevation.
• Stay hydrated: Dehydration can exacerbate tissue damage and impair recovery. Adequate fluid intake supports organ function and cellular health.
• Eat a balanced diet: Ensure adequate intake of B12, folate, iron, and other nutrients essential for healthy blood cell production. This is particularly important for vegetarians and vegans, who are at higher risk of B12 deficiency.

When Should You Get Tested?

LDH testing may be appropriate if:

• You have symptoms suggestive of anaemia (fatigue, pallor, breathlessness) and haemolysis is suspected
• You are being investigated or monitored for lymphoma, leukaemia, or testicular cancer
• You have unexplained muscle pain or dark urine after exercise
• You have signs of liver disease or organ damage
• You have a pleural effusion or ascites requiring diagnostic characterisation
• You are receiving chemotherapy and LDH is used to monitor treatment response
• You have a suspected severe infection or inflammatory condition

LDH is typically ordered as part of a broader panel of investigations rather than in isolation. Your doctor will interpret the result alongside your full blood count, liver function tests, kidney function, and other relevant markers to build a complete clinical picture.

Which Lola Health Tests Include LDH?

Lola Health offers comprehensive blood testing that can include markers relevant to tissue health and cellular integrity:

• Peak Insights - Our most extensive health panel, providing a thorough assessment of your health across multiple organ systems, including markers of cellular health and blood cell integrity.
• Vital Check — A detailed wellness assessment covering essential biomarkers to monitor your health and identify potential concerns early.
• Core Health — An essential health check covering foundational biomarkers for a clear overview of your overall wellbeing.

All Lola Health tests use venous blood draws performed by qualified phlebotomists for medical-grade accuracy. Results are reviewed by GP-certified professionals and delivered with personalised health recommendations.