Which laboratory tests are considered negative acute-phase reactants?

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Last updated: May 6, 2026 • View editorial policy

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Negative Acute Phase Reactants

The primary negative acute phase reactants are albumin, prealbumin (transthyretin), transferrin, retinol-binding protein, and antithrombin. These proteins decrease in serum concentration during inflammation, infection, trauma, or acute illness, making them unreliable markers of nutritional status in these contexts.

Core Negative Acute Phase Reactants

Albumin

  • Most commonly measured negative acute phase protein 1, 2
  • Decreases during acute or chronic inflammation independent of nutritional status
  • Half-life of approximately 20 days 1
  • Serves as a marker of disease severity and inflammatory status rather than nutrition 3, 4
  • Critical caveat: Low albumin reflects inflammation, not necessarily malnutrition 2, 3

Prealbumin (Transthyretin)

  • Negative acute phase reactant with shorter half-life (2-3 days) than albumin 1
  • Serum levels decline in response to inflammation or infection 1
  • Levels <30 mg/dL warrant evaluation for protein-energy malnutrition in stable patients 1
  • More sensitive to acute changes but equally affected by inflammation 1, 5
  • Particularly unreliable in critically ill, trauma, and burn patients 5

Transferrin

  • Negative acute phase reactant with 8-day half-life 1
  • Additional confounding factor: Levels increase with iron deficiency and decrease with iron loading 1
  • Less clinically useful than albumin in dialysis patients due to effects of blood loss, erythropoietin therapy, and IV iron 1
  • Transferrin saturation (TSAT) reflects available iron for erythropoiesis but is also affected by inflammation 6

Retinol-Binding Protein

  • Negative acute phase reactant affected by inflammation 2
  • Part of the BRINDA (Biomarkers Reflecting Inflammation and Nutritional Determinants of Anemia) adjustment equations 2

Antithrombin

  • Acts as a negative acute phase protein 7
  • Decreases in sepsis and after major surgery due to IL-6 mediated acute phase response 7
  • Reduction occurs without evidence of coagulation activation 7

Clinical Implications

When Inflammation is Present

C-reactive protein (CRP) should be measured simultaneously with any micronutrient or protein analysis 2. The impact of inflammation typically appears with CRP levels >20 mg/L 2.

  • Within 24 hours of elective surgery, plasma concentrations of many trace elements and vitamins fall markedly without actual change in whole body status 2
  • Inflammation causes redistribution of micronutrients from circulation to other organs 2
  • Low blood levels do not necessarily indicate deficiency or depletion during acute inflammation 2

Specific Clinical Contexts

In critically ill/ICU patients 3, 4, 5:

  • Albumin and prealbumin are unreliable nutritional markers
  • They function as markers of illness severity rather than nutritional status
  • Massive resuscitation invalidates weight and BMI measurements
  • Alternative assessment methods (NRS-2002, mNUTRIC scores) should be used

In chronic kidney disease/dialysis patients 1:

  • Prealbumin levels are elevated due to impaired renal degradation
  • Target prealbumin ≥30 mg/dL in stable maintenance dialysis patients
  • Transferrin interpretation complicated by chronic blood loss and erythropoietin therapy

In inflammatory bowel disease 8:

  • Many serum micronutrient markers are positive or negative acute phase reactants
  • Ferritin and copper increase with inflammation
  • Folate, selenium, and zinc decrease with inflammation
  • Measurement reliability questionable during active disease

Positive Acute Phase Reactants (For Contrast)

The following increase during inflammation 6, 9, 10:

  • Ferritin: Acute phase reactant that can mask depleted iron stores 6, 9
  • Ceruloplasmin: Increases during inflammation 11
  • C-reactive protein (CRP): Primary marker of inflammation 2, 3
  • Fibrinogen: Increases 2.8-2.9 fold with IL-6 stimulation 7

Vitamin D as Negative Acute Phase Reactant

Serum 25-(OH)D decreases following acute inflammatory insult 12. Following elective orthopedic surgery, serum 25-(OH)D decreased from 56.2 to 46.0 nmol/L within 48 hours as CRP increased from 5.0 to 116.0 mg/L 12. This makes serum 25-(OH)D an unreliable biomarker of vitamin D status after acute inflammatory events 12.

Practical Algorithm for Interpretation

  1. Always measure CRP concurrently with nutritional markers 2
  2. If CRP >20 mg/L: Interpret low albumin, prealbumin, transferrin, and retinol-binding protein as reflecting inflammation, not necessarily nutritional deficiency
  3. If CRP normal: These markers more reliably reflect nutritional status
  4. In chronic inflammation: Consider measuring markers during clinical remission when possible 8
  5. Use positive-to-negative acute phase reactant ratios: Ferritin-to-transferrin or ceruloplasmin-to-transferrin ratios may better reflect inflammatory burden 11

References

2
Guideline

espen micronutrient guideline.

Clinical Nutrition, 2022

12
Research

Vitamin D: a negative acute phase reactant.

Journal of clinical pathology, 2013

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.