What does a low lactate dehydrogenase (LDH) level of 118 U/L indicate?

Low LDH of 118 U/L: Clinical Significance

A low LDH level of 118 U/L is generally not clinically significant and does not indicate pathology. LDH is primarily used as a marker of tissue damage, cell death, and high cellular turnover, so low values lack the diagnostic and prognostic utility of elevated levels 1, 2.

Why Low LDH Is Not Clinically Meaningful

• LDH serves as a biomarker only when elevated, reflecting conditions such as hemolysis, tissue injury, malignancy, or inflammation 1, 2, 3.
• The clinical literature focuses exclusively on elevated LDH thresholds—for example, LDH >1.5× upper limit of normal (ULN) for cancer prognostication, LDH >10× ULN as a marker of severe illness with >50% mortality, and specific cut-offs for pleural effusion classification 1, 4.
• No established disease states or adverse outcomes are associated with low LDH values 1, 2.

Normal Reference Range Context

• Typical laboratory reference ranges for serum LDH are approximately 140–280 U/L (though this varies by laboratory method), meaning 118 U/L falls just below the lower limit of normal 5, 4.
• LDH is a ubiquitous cytoplasmic enzyme present in all major organ systems; its activity reflects ongoing cellular metabolism rather than a specific physiologic function in serum 2, 3.
• Mild reductions below the reference range do not indicate metabolic dysfunction or organ pathology 2.

When to Investigate Further

• Repeat the test if the sample was hemolyzed, because in-vitro hemolysis falsely elevates LDH, but processing errors could theoretically affect results 1.
• Consider the clinical context: if the patient has unexplained symptoms (fatigue, anemia, organ dysfunction), pursue targeted workup for those symptoms rather than attributing them to low LDH 1, 2.
• Do not order LDH isoenzyme analysis for low total LDH, as isoenzyme fractionation is reserved for identifying the tissue source of elevated LDH 5.

Practical Algorithm

1. Confirm the value is accurate by checking for sample integrity and laboratory error 1.
2. Assess whether the patient has any clinical symptoms that prompted LDH testing 1, 2.
3. If asymptomatic and no other laboratory abnormalities exist, no further action is needed 2.
4. If symptomatic, direct workup toward the specific clinical presentation (e.g., anemia workup for fatigue, hepatic panel for liver symptoms) rather than pursuing low LDH as an isolated finding 1, 2.

Common Pitfalls to Avoid

• Do not over-interpret low LDH as a sign of disease; the enzyme has no established lower threshold for pathology 1, 2.
• Avoid ordering serial LDH measurements to "monitor" low values, as this practice lacks evidence-based utility 1, 2.
• Do not confuse low LDH with low lactate; lactate is a separate metabolic marker used primarily in shock and tissue hypoperfusion, whereas LDH is an enzyme marker of cell injury 6, 7.