Unit Converter
Prealbumin
(Short-Half-Life Protein - Sensitive Marker for Nutritional Status, Inflammation & Acute Illness)
Synonyms
- Prealbumin
- Transthyretin (TTR)
- Thyroxine-binding prealbumin
- Plasma prealbumin
- PA
Units of Measurement
- µmol/L
- g/L
- mg/dL
- mg/100 mL
- mg%
- mg/mL
Molecular Weight
~55 kDa (tetrameric protein)
Key Unit Conversions
Mass ↔ Molar
(MW ≈ 55,000 g/mol)
1 mg/dL=10 mg/L1\ \text{mg/dL} = 10\ \text{mg/L}1 mg/dL=10 mg/L 1 mg/L=0.0182 µmol/L1\ \text{mg/L} = 0.0182\ \text{µmol/L}1 mg/L=0.0182 µmol/L 1 µmol/L=55 mg/L1\ \text{µmol/L} = 55\ \text{mg/L}1 µmol/L=55 mg/L
mg%
\text{mg%} = \text{mg/dL}
mg/mL
1 mg/mL=1000 mg/dL1\ \text{mg/mL} = 1000\ \text{mg/dL}1 mg/mL=1000 mg/dL
Description
Prealbumin (transthyretin) is a transport protein synthesized primarily in the liver, responsible for carrying:
- Thyroxine (T4)
- Retinol-binding protein (RBP) + Vitamin A
It has a short half-life (2–3 days), making it highly sensitive to changes in:
- Nutritional status
- Protein-calorie intake
- Acute inflammation
- Liver synthetic function
Unlike albumin (half-life 20 days), prealbumin responds quickly to metabolic changes, which is why it is widely used in nutritional assessment.
Physiological Role
- Transports T4 to tissues
- Forms complex with RBP to transport retinol (vitamin A)
- Reflects hepatic protein synthesis
- Very sensitive to cytokine-mediated suppression during inflammation
Clinical Significance
LOW Prealbumin (Most Important Finding)
Associated with:
1. Malnutrition / Protein-Calorie Malnutrition
- Kwashiorkor
- Severe undernutrition
- Chronic illness with poor intake
- Elderly / frailty
- Eating disorders
2. Liver Disease
- Cirrhosis
- Hepatitis
- Liver failure
- Acute alcoholic hepatitis
3. Critical Illness / Inflammation
Decrease due to:
- IL-6
- TNF-α
- CRP elevation
4. Acute and Chronic Illness
Seen in:
- Sepsis
- Burns
- Trauma
- Postoperative states
- Nephrotic syndrome (loss in urine)
5. Malabsorption
- Celiac disease
- Crohn’s
- Pancreatic insufficiency
- Short bowel syndrome
Symptoms of low levels
Indirect — reflect catabolic state, muscle wasting, poor immunity.
HIGH Prealbumin
Less common.
Causes:
- High-dose corticosteroids
- Dehydration
- Hodgkin lymphoma
- Anabolic steroid use
- Renal failure (reduced clearance)
High levels are usually not clinically concerning.
Reference Intervals
Adults
- 0.20 – 0.40 g/L
(= 20 – 40 mg/dL)
(= 200 – 400 mg/L)
(= 3.6 – 7.2 µmol/L)
Mild depletion
- 15 – 20 mg/dL
Moderate depletion
- 10 – 15 mg/dL
Severe depletion
- < 10 mg/dL
Children
Higher levels due to growth demands.
Critical range
- < 5 mg/dL → severe malnutrition / critical illness
1. Nutritional Status (Primary Use)
Assesses:
- Protein intake
- Caloric adequacy
- Nutritional risk
- Response to feeding interventions
Used in:
- Hospitalized patients
- ICU
- Long-term care
- Pre- and postoperative nutrition evaluation
2. Monitoring Nutrition Therapy
- Parenteral nutrition (TPN)
- Enteral feeding
- Refeeding in malnourished patients
3. Liver Function Assessment
Prealbumin is sensitive to decreased liver synthetic function.
4. Inflammatory States
Low prealbumin signals acute-phase negative response.
5. Chronic Disease Severity
Useful in:
- Heart failure
- COPD
- Cancer cachexia
- Chronic infections
6. Renal Failure
Levels may rise due to reduced clearance.
Analytical Notes
- Serum or plasma sample
- Fasting not required
- Inflammation (high CRP) suppresses synthesis, lowering level independent of nutrition
- Useful only when interpreted with CRP
- Rapid response → useful for short-term monitoring (every 2–3 days)
Clinical Pearls
- Prealbumin is NOT a standalone nutrition marker - always interpret with CRP.
- Low levels may reflect inflammation, not malnutrition.
- Albumin + prealbumin together provide insight into liver synthesis and nutritional state.
- Levels rise within 3–5 days of adequate nutrition therapy.
- Renal failure elevates prealbumin due to reduced clearance.
Interesting Fact
The name “prealbumin” came from its location on early electrophoresis gels - it migrated ahead of albumin, not because it is a precursor.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Protein Analysis
- ASPEN Clinical Nutrition Guidelines - Protein Markers
- Mayo Clinic Laboratories - Prealbumin
- ARUP Consult - Nutrition & Protein Markers
- MedlinePlus / NIH - Prealbumin Test