Tighter precision target required for lactate testing in patients with lactic acidosis

Area of Science:

• Clinical Chemistry
• Medical Diagnostics
• Biostatistics

Background:

• Allowable analytic errors are typically based on biologic variation in healthy individuals.
• Blood lactate, often at low concentrations in healthy subjects, exhibits large allowable variation when expressed as a coefficient of variation (CV).
• Established data suggests a pooled intra-individual lactate variation (si) of 27%, leading to a desirable imprecision of 13.5%.

Purpose of the Study:

• To derive biologic variability (sb) for blood lactate from consecutive patient data.
• To demonstrate that the biologic variability (sb) of lactate is significantly lower than previously reported.
• To establish more accurate allowable error limits for lactate measurements.

Main Methods:

• Lactate results from 54,000 measurements over 18 months in an intensive care unit (ICU) were analyzed.
• Standard deviations of duplicates (SDD) were calculated for intra-patient lactates at various time intervals (0-16 hours).
• Biologic variability (sb) was derived using linear regression analysis of SDD versus time interval, accounting for analytic variation (sa).

Main Results:

• The study demonstrated that the biologic variability (sb) of lactate is significantly lower than previously estimated.
• The relative desirable imprecision for patients with lactic acidosis was found to be approximately half that of normal individuals.
• The derivation of sb was performed across multiple patient lactate ranges.

Conclusions:

• Current allowable error limits for lactate measurements are generally too high.
• Evaluations of lactate measurements necessitate the use of tighter, more accurate allowable error limits.
• These findings have implications for the precision and reliability of lactate diagnostics in clinical settings.