Lactate Dehydrogenase-L

1. What is Lactate Dehydrogenase (LDH)?

Lactate Dehydrogenase (LDH) is an intracellular enzyme present in almost all body tissues. It catalyzes the reversible conversion:

Lactate ⇌ Pyruvate
(with interconversion of NADH ⇌ NAD⁺)

Because LDH is located inside cells, it is released into the bloodstream when tissues are damaged.

2. Normal Reference Range

• Adults: ~140–280 U/L
  (Ranges vary slightly depending on laboratory method.)

3. Clinical Significance of Elevated LDH

LDH is a non-specific marker of tissue damage. Elevated levels indicate cell injury but do not pinpoint the exact cause without further testing.

A. Cardiac Conditions

• Previously used in diagnosis of myocardial infarction (MI)

• LDH rises:

  • 12–24 hours after MI

  • Peaks at 48–72 hours

  • Returns to normal in 7–10 days

• LDH1 > LDH2 (“LDH flip”) was suggestive of MI
  (Now largely replaced by troponin testing.)

B. Liver Diseases

• Acute hepatitis

• Cirrhosis

• Hepatic necrosis
  LDH rises due to hepatocyte damage.

C. Hemolytic Anemia

• LDH markedly increased due to RBC destruction

• Seen in:

  • Hemolytic anemia

  • Megaloblastic anemia

  • Transfusion reactions

D. Malignancies

LDH is often elevated in:

• Lymphoma

• Leukemia

• Germ cell tumors

• Metastatic cancers

Clinical Use:

• Tumor burden assessment

• Prognostic indicator

• Monitoring treatment response

High LDH often correlates with aggressive disease.

E. Pulmonary Conditions

• Pulmonary embolism

• Pneumonia

• Pneumocystis jirovecii infection (notably elevated LDH)

F. Muscle Injury

• Muscular dystrophy

• Trauma

• Rhabdomyolysis

G. Renal Diseases

• Acute kidney injury

• Renal infarction

4. Causes of Decreased LDH

Rare and usually not clinically significant:

• High vitamin C intake

• Certain genetic deficiencies

5. Key Clinical Points

✔ LDH is a marker of tissue breakdown
✔ Non-specific — must be interpreted with other tests
✔ Useful in oncology for prognosis
✔ Helpful in hemolysis evaluation
✔ Historically used in MI diagnosis