Patient hydration: a major source of laboratory uncertainty

Area of Science:

• Physiology
• Clinical Chemistry
• Laboratory Medicine

Background:

• Body water movement between intravascular, extravascular, intracellular, and extracellular spaces is governed by physiological forces.
• Ernest Starling's 1896 principles still explain fluid transfer mechanisms relevant today.
• The clinical consequences of fluid shifts on laboratory results are often underestimated.

Purpose of the Study:

• To highlight the impact of body fluid shifts on clinical laboratory test values.
• To emphasize patient hydration status as a crucial pre-analytical variable.
• To underscore the need for addressing fluid shifts in routine clinical laboratory practice.

Main Methods:

• Review of physiological principles governing fluid distribution.
• Analysis of factors influencing body water shifts, including posture and environmental effects.
• Examination of the impact of hydration on laboratory analyte values, particularly colloid analytes.

Main Results:

• Fluid shifts can cause significant variations in laboratory test results.
• Patient posture and environmental factors demonstrably affect fluid distribution and test values.
• Hydration status critically influences results for colloid analytes within narrow interpretive ranges.

Conclusions:

• Patient hydration status is a major pre-analytical variable impacting laboratory diagnostics.
• Failure to account for fluid shifts can lead to misinterpretation of clinical data.
• Clinical laboratories and clinicians must recognize and address hydration's effect on test results for accurate patient care.