Serum Lactate Dehydrogenase in Paediatrics

Also written as Lactate Dehydrogenase.

LDH is a cytoplasmic enzyme released on cell injury. In children it flags hemolysis, tissue necrosis or tumour burden. Interpretation must consider local disease patterns and test availability.

Definition and diagnosis

LDH is an intracellular enzyme converting lactate to pyruvate. Serum elevation indicates cell turnover or damage. Reference range 140–280 U/L in most labs; local ranges may differ.

• LDH level: Elevated LDH suggests hemolysis, myocarditis, sepsis, tumour, or tissue necrosis; normal LDH does not exclude disease if other markers are abnormal.

• Enzyme present in all cells; released on injury
• Measured by spectrophotometric assay

Severity and staging

LDH is not a staging tool alone but correlates with disease burden. In haemolytic anaemias, a 2–3 fold rise is significant; in malignancy, >500 U/L may indicate high tumour load.

• LDH 300–500 U/L – mild elevation
• >500 U/L – marked elevation, consider tumour or severe infection

Causes, most likely first

In East Africa, the top causes of raised LDH in children are hemolysis, sepsis, malaria, and tumour. Other contributors include sickle cell crisis, TB, and herbal nephrotoxicity.

• Hemolysis – malaria, sickle cell, G6PD deficiency
• Sepsis – bacterial meningitis, septicaemia
• Malaria – Plasmodium falciparum
• Tumour – lymphoma, leukemia
• Other – TB, hepatitis B, herbal remedies

How it presents

Raised LDH is usually silent; it is inferred from clinical context: jaundice, pallor, fever, lymphadenopathy, or unexplained anaemia. It may accompany other lab abnormalities such as low haptoglobin or high bilirubin.

• Anaemia with jaundice – think hemolysis
• Fever with lymphadenopathy – consider lymphoma

Investigations

LDH is a screening marker; confirm the underlying cause with targeted tests. When LDH is high, look for hemolysis, infection, or tumour.

• Peripheral blood smear: Schistocytes suggest mechanical hemolysis; parasites confirm malaria.
• Haptoglobin: Low haptoglobin indicates hemolysis.
• Direct antiglobulin test (Coombs): Positive Coombs indicates autoimmune hemolysis.
• Blood cultures: Positive cultures confirm sepsis.
• Chest X‑ray: Suggests pneumonia or TB.
• Ultrasound abdomen: Detects hepatosplenomegaly or abdominal masses.
• Bone marrow aspirate: Reveals blasts or dysplasia.
• Malaria rapid diagnostic test: Positive RDT confirms malaria.

Red flags and complications

Severe LDH elevation with haemolysis can lead to acute kidney injury, hypovolaemia, and shock. In tumour, it may herald tumour lysis syndrome.

• Acute kidney injury – monitor urine output
• Shock – monitor vitals
• Tumour lysis – monitor electrolytes

Management

Treat the underlying cause first. Supportive care includes transfusion for severe anaemia, antibiotics for sepsis, antimalarials for malaria, and chemotherapy for lymphoma. Monitor LDH to gauge response.

• Antimalarials – artesunate or quinine
• Broad‑spectrum antibiotics – ceftriaxone or ampicillin
• Transfusion – packed RBCs
• Chemotherapy – standard paediatric protocols

Follow‑up and prevention

Repeat LDH every 48–72 hours in acute settings. Prevent malaria with bed nets, treat sickle cell with hydroxyurea, and counsel on safe herbal use.

• Repeat LDH 48–72 hrs
• Malaria prophylaxis
• Hydroxyurea for sickle cell

Often confused with

Elevated LDH can mimic other conditions: high AST/ALT in liver disease, or high CK in rhabdomyolysis. Context and additional tests differentiate them.

• AST/ALT – liver injury
• CK – muscle breakdown

Where results can mislead

LDH can be falsely normal in early haemolysis or low in chronic disease. Interfering substances (hemolysis of sample) can spuriously raise LDH.

• Early haemolysis – LDH may still be normal
• Sample haemolysis – artifactual rise

Questions an examiner may ask

• A 7‑year‑old with fever, pallor, and jaundice has an LDH of 650 U/L. What is the most likely diagnosis? — Malaria or sickle cell crisis; confirm with RDT or smear. A 4‑year‑old with pneumonia has an LDH of 520 U/L. What does this suggest? — Severe tissue injury or sepsis; check cultures and support. A child with lymphoma has an LDH of 800 U/L. What complication must you monitor? — Tumour lysis syndrome; monitor electrolytes. A 2‑year‑old with suspected hemolysis has normal LD

When to seek help

• Severe anaemia with hypotension
• Unexplained shock
• Acute kidney injury
• Signs of tumour lysis syndrome

Quick questions

Why is LDH not specific?

LDH is released from all cells; many conditions raise it, so it must be interpreted with clinical context.

Can I rely on LDH to diagnose malaria?

No; use a malaria RDT or microscopy. LDH rises in malaria but is not diagnostic alone.

What is the threshold for concern in a child with sickle cell?

An LDH >500 U/L in a sickle cell child suggests a crisis or hemolysis and warrants urgent review.