What are normal Lactate Dehydrogenase (LDH) values?

Normal Lactate Dehydrogenase (LDH) Values

Normal LDH values in adults typically range from 125-220 U/L (or IU/L), though reference ranges may vary slightly between laboratories depending on the testing methodology used.

Understanding LDH

Lactate dehydrogenase (LDH) is an enzyme found in nearly all cells of the body, with particularly high concentrations in the heart, liver, muscles, kidneys, lungs, and blood cells. It plays a crucial role in cellular energy production by catalyzing the conversion of lactate to pyruvate.

Key characteristics of LDH:

• Present in virtually all tissues in the body
• Released into the bloodstream when cells are damaged or destroyed
• Exists in five different isoenzymes (LDH-1 through LDH-5), each predominant in different tissues
• Measured as total LDH in routine clinical practice

Normal Reference Ranges

While the exact reference range may vary slightly between laboratories, normal LDH values typically fall within these parameters:

• Adults: 125-220 U/L (or IU/L)
• Children: May have slightly higher values than adults
• Newborns: Can have significantly higher values that gradually decrease to adult levels

Clinical Significance of Abnormal LDH Values

Elevated LDH

LDH levels may be elevated in numerous conditions:

• Cancer:

  • Markedly elevated in hematologic malignancies (>900 IU/L) 1
  • Moderately elevated in solid tumors and metastatic disease 1
  • Serves as a prognostic factor in various cancers including small cell lung cancer 2

• Tissue damage:

  • Cardiac injury (though troponin has largely replaced LDH for this purpose) 1
  • Liver disorders
  • Muscle disorders
  • Hemolysis

• Other conditions:

  • Infections
  • Preeclampsia 2
  • Renal conditions

Degree of LDH Elevation

The magnitude of LDH elevation can sometimes provide diagnostic clues:

• Mild elevation (1-2× normal): Often nonspecific
• Moderate elevation (2-3× normal): Seen in various conditions including solid tumors
• Marked elevation (>3× normal): More commonly seen in hematologic malignancies, particularly acute lymphoblastic leukemia 3
• Severe elevation (>10× normal): Associated with poor prognosis regardless of underlying cause (mortality rate >50%) 4

Clinical Applications of LDH Testing

Diagnostic Applications

• Pleural effusions: Component of Light's criteria to distinguish exudative from transudative effusions (PF LDH >67% of the upper limit of normal serum value suggests exudate) 2

• Cancer monitoring:

  • Mandatory tumor marker for advanced germ cell tumors 1
  • Prognostic factor in multiple malignancies 2, 1

Monitoring Applications

• Treatment response: Normalization during follow-up suggests effective treatment 1, 4
• Disease progression: Rising levels may indicate progression or therapeutic failure 1, 4

Interpretation Considerations

• LDH should always be interpreted in context with other clinical and laboratory findings due to its low specificity 1
• Serial measurements provide greater value than single determinations 1
• Elevated LDH without obvious cause warrants thorough investigation, as it may be an early marker of occult malignancy 5

Practical Recommendations

When encountering elevated LDH levels:

1. Consider the degree of elevation (mild, moderate, marked, severe)
2. Correlate with clinical presentation and other laboratory findings
3. Consider additional testing as appropriate:
   • Complete blood count
   • Liver and renal function tests
   • Inflammatory markers
   • Cardiac markers if cardiac involvement suspected
   • Imaging studies based on clinical suspicion

Remember that while LDH is a sensitive marker of tissue damage, it lacks specificity and should never be used in isolation for diagnostic purposes.