Patient hydration: a major source of laboratory uncertainty

Abstract

Movement of body water from compartment to compartment during any time period is attributable to forces active within and upon each space. The result of these forces leads to transfer of water between intravascular and extravascular compartments, as well as shifts between extracellular and intracellular spaces. The importance of these shifts and of the associated mechanism was described by Ernest Starling in 1896 in very much the same manner as it is viewed today. The end result of fluid transfer and its physiological and laboratory consequences has not been fully appreciated. Despite awareness that fluid shifts can affect laboratory analytical results, little recent investigation has addressed the problem in the routine clinical laboratory. Thus, the potential for significant misinterpretation remains. For example, it is known that individual laboratory test values can vary widely, depending on many factors including the subject's posture during and immediately before phlebotomy, leading to significant changes in the interpretation of blood analyte values. Furthermore, a variety of ubiquitous environmental effects have additional impact on fluid distribution and thus on test values. In other words, patient hydration status is a major pre-analytical variable that needs to be addressed by the clinical laboratory. The need to adjust data for patient hydration status is especially important in the case of colloid analytes for which the dynamic range includes a narrow "gray zone" where hydration changes of a few percentage points can change the clinical implications. The crucial importance of this adjustment is underscored by the fact that neither the testing laboratory nor the clinician are aware of this unseen circumstance and are thus compelled to work with data that do not necessarily reflect the clinical situation.

Comparison of clinical and biochemical markers of dehydration with the clinical dehydration scale in children: a case comparison trial

“…Body water movement from compartment to compartment during any time period can be attributed to forces active within and upon each space. These forces lead to water transfer between intravascular and extravascular compartments and shifts between extracellular and intracellular spaces [28], and may be independent of body weight.…”

Chronic stress and body composition disorders: implications for health and disease

“…Apart from water losses, dehydration may also result from shifts in water compartment redistribution; these water shifts are exaggerated by the actions of cortisol [27,28]. ANP increases glomerular filtration rate and the sodium filtration fraction, reduces cardiac output, and inhibits both renin secretion and the aldosterone response to angiotensin [29].…”

Transthyretin, nutrition, and inflammation: response to Dr. Bernstein

“…At these ages, this is certainly not all due to ''wound healing'', especially since the reference intervals derived by Ritchie et al were based on a very large cohort of individuals without evidence of significant disease. TTR in hospitalized patients One additional and important variable that we mentioned in the paper but did not discuss in detail is the effect of position and hydration on protein concentrations (9). Patients who are bedridden have reduced concentrations of essentially all serum protein analytes, in the general range of approximately 10%.…”