Unit Converter
Retinol (Vitamin A1)

SI UNITS (recommended)

CONVENTIONAL UNITS

(Fat-Soluble Vitamin Essential for Vision, Immunity, Growth & Epithelial Health)

Synonyms

  • Retinol
  • Vitamin A₁
  • Preformed vitamin A
  • All-trans-retinol
  • Serum retinol
  • Retinoid alcohol

Units of Measurement

  • µmol/L
  • µg/L
  • µg/dL
  • µg/100 mL
  • µg%
  • ng/mL

Unit Conversions

Molecular weight of Retinol = 286.45 g/mol

µmol/L ↔ µg/L

1 µmol/L=286.45 µg/L1\ \text{µmol/L} = 286.45\ \text{µg/L}1 µmol/L=286.45 µg/L 1 µg/L=0.00349 µmol/L1\ \text{µg/L} = 0.00349\ \text{µmol/L}1 µg/L=0.00349 µmol/L

µg/dL → µg/L

1 µg/dL=10 µg/L1\ \text{µg/dL} = 10\ \text{µg/L}1 µg/dL=10 µg/L

µg% = µg/dL

(Older clinical unit.)

ng/mL → µg/L

1 ng/mL=1 µg/L1\ \text{ng/mL} = 1\ \text{µg/L}1 ng/mL=1 µg/L

Description

Retinol (Vitamin A₁) is a fat-soluble vitamin essential for:

  • Vision (retinal pigments, low-light vision)
  • Immune function
  • Epithelial differentiation
  • Growth and development
  • Reproduction
  • Antioxidant mechanisms (via retinoids)

Retinol circulates in blood bound to:

  • Retinol-binding protein (RBP)
  • Transthyretin (TTR)

Vitamin A is obtained from:

  • Animal sources (retinyl esters, retinol)
  • Plant carotenoids (converted into retinol)

Physiological Role

Vision

Essential component of rhodopsin, required for scotopic (low-light) vision.

Immunity

Maintains mucosal surfaces and immune-cell differentiation.

Skin & Epithelia

Supports epithelial cell turnover and keratinization control.

Reproduction

Critical for spermatogenesis and placental health.

Growth

Important for bone growth and fetal development.

Clinical Significance

LOW RETINOL

Major Causes

  • Malnutrition
  • Fat malabsorption
    • Cystic fibrosis
    • Celiac disease
    • Chronic pancreatitis
  • Liver disease (low storage)
  • Protein deficiency (low RBP)
  • Bariatric surgery
  • Chronic infection/inflammation

Symptoms

  • Night blindness (nyctalopia) – earliest sign
  • Xerophthalmia
  • Bitot spots
  • Keratomalacia (severe)
  • Dry skin
  • Poor immunity
  • Recurrent infections
  • Growth failure in children

HIGH RETINOL

Usually due to supplement overuse, not diet.

Symptoms

  • Headache, irritability
  • Bone pain
  • Hepatotoxicity
  • Peeling skin
  • Pseudotumor cerebri
  • Teratogenicity (in pregnancy)

Reference Intervals

(Tietz 8E + NIH/ODS + WHO + Mayo + ARUP)

Adults

  • 1.05 – 2.80 µmol/L
     (= 300 – 800 µg/L)
    (= 30 – 80 µg/dL)
    (= 30 – 80 ng/mL)

Children

  • 0.70 – 2.00 µmol/L

Deficiency Cutoff

  • <0.70 µmol/L (200 µg/L) = Vitamin A deficiency
  • <0.35 µmol/L (100 µg/L) = Severe deficiency, risk of xerophthalmia

Toxicity Threshold

  • >3.50 µmol/L (1000 µg/L)

Diagnostic Uses

1. Evaluation of Night Blindness / Xerophthalmia

Key test in deficiency.

2. Malnutrition & Malabsorption

Retinol falls early in:

  • Cystic fibrosis
  • Crohn disease
  • Pancreatic insufficiency

3. Chronic Liver Disease

Storage deficiency → low levels.

4. Monitoring Vitamin A Supplementation

5. Pediatric Growth Disorders

Especially in resource-limited areas.

6. Infections

Acute infection may lower retinol transiently due to decreased RBP.

Analytical Notes

  • Requires fasting sample (12 hours)
  • Light-sensitive → protect from light
  • Sample type: serum
  • Measured via HPLC or LC–MS/MS
  • Inflammation can lower retinol independent of true deficiency
  • Interpret together with RBP (Retinol-Binding Protein) if needed

Clinical Pearls

  • Night blindness is the earliest clinical sign of deficiency.
  • In pregnancy, avoid high-dose supplements due to teratogenic risk.
  • In liver disease, low retinol reflects reduced storage capacity.
  • Retinol falls during acute infection; repeat testing after recovery.
  • Serum retinol does not reflect body stores until deficiency is moderate to severe.

Interesting Fact

Vitamin A deficiency is one of the leading causes of preventable childhood blindness globally, and WHO recommends high-dose supplementation in high-risk regions.

References

  1. Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Vitamins
  2. WHO - Vitamin A Deficiency Surveillance Guidelines
  3. NIH Office of Dietary Supplements - Vitamin A Fact Sheet
  4. Mayo Clinic Laboratories - Retinol
  5. ARUP Consult - Vitamin A
  6. CDC Micronutrient Guidelines

Last updated: January 27, 2026

Reviewed by : Medical Review Board

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