Biochemical Markers of Nutritional Status

Biochemical markers of nutritional status are laboratory measurements - in blood, urine, or tissue - used to estimate circulating nutrient levels, body stores, and the metabolic context in which they are interpreted. They complement anthropometric and clinical data but must be read in light of inflammation and disease, which can shift many markers independently of nutrient intake.

Definition

Biochemical markers of nutritional status are measurable laboratory indicators - such as serum proteins, micronutrient concentrations, and inflammatory markers - used together to characterise nutritional status while accounting for the metabolic and inflammatory context.

Scope

The entry covers the main classes of nutritional biomarkers (serum proteins, micronutrient and vitamin concentrations, and markers of inflammation) and the central caveat that acute-phase responses alter several commonly used indices. It is a methodological reference that explains how markers are interpreted, not a guide to ordering tests or treating deficiencies in an individual.

Core questions

• Which biochemical markers reflect nutrient stores versus the inflammatory state?
• Why are serum proteins such as albumin no longer treated as direct markers of nutrition?
• How should inflammation be accounted for when interpreting nutritional biomarkers?

Key concepts

• Serum hepatic proteins (albumin, prealbumin/transthyretin)
• Acute-phase response and C-reactive protein
• Micronutrient and vitamin concentrations
• Negative acute-phase reactants
• Confounding by inflammation
• Markers as adjuncts, not stand-alone diagnostics

Mechanisms

Many biochemical markers respond to more than nutrient supply. Hepatic proteins such as albumin and transthyretin fall during the acute-phase response because the liver redirects synthesis toward inflammatory proteins, so low levels often signal inflammation and disease severity rather than protein intake. Micronutrient concentrations can likewise be redistributed during inflammation. Interpreting nutritional biomarkers therefore requires pairing them with markers of inflammation (such as C-reactive protein) and with clinical context, which is why current frameworks treat them as supporting rather than defining evidence.

Clinical relevance

Biochemical markers add objective, quantitative information to nutritional assessment and help flag deficiencies and inflammatory burden. As reference material this entry explains how such markers are interpreted within their metabolic context; it is descriptive and does not direct laboratory ordering or correction of abnormalities for any individual.

Epidemiology

Population nutrition surveys use biomarkers to estimate the prevalence of micronutrient deficiencies, and the recognition that serum proteins track inflammation has reshaped how malnutrition is defined in clinical consensus statements.

Evidence & guidelines

The review by Fuhrman et al. (2004) summarised the evidence that hepatic proteins reflect inflammation more than nutrition, a position reflected in the ASPEN/AND consensus (White et al., 2012), which omitted serum albumin as a defining characteristic of malnutrition. The GLIM framework (Cederholm et al., 2019) treats inflammation as an etiologic criterion rather than relying on protein markers as a phenotype.

History

For much of the twentieth century serum albumin and prealbumin were used as nutritional indices. Accumulating evidence through the 1990s and 2000s, synthesised by Fuhrman and colleagues in 2004, showed these proteins behave as negative acute-phase reactants; subsequent consensus statements (2012) and the GLIM criteria (2019) accordingly demoted them from defining markers to context-dependent adjuncts.

Debates

Are serum proteins valid markers of nutritional status?

Albumin and prealbumin fall with inflammation independent of intake, so contemporary frameworks no longer treat them as direct nutritional markers, though they retain prognostic value for illness severity.

Key figures

• Mandy Fuhrman
• Gordon Jensen
• Jane White

Seminal works

• fuhrman-2004
• white-2012
• cederholm-2019-glim

Frequently asked questions

Why is serum albumin no longer used as a nutritional marker?

Albumin is a negative acute-phase reactant: its concentration falls during inflammation and illness independently of protein intake, so a low level more often reflects disease severity than malnutrition, and major consensus frameworks have removed it as a defining characteristic.

How should inflammation be considered when reading nutritional biomarkers?

Markers of inflammation such as C-reactive protein are interpreted alongside nutritional biomarkers so that changes driven by the acute-phase response are not mistaken for changes in nutrient stores or intake.