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Vitamin A
| Category | Biochemistry |
|---|---|
| Turnaround time | 2 weeks |
Additional information
Background
Vitamin A, also known as retinol, is a fat-soluble vitamin obtained from dietary intake. Intake is either as pre-formed vitamin A, eg from dairy, oily fish, liver and liver products, or is converted from plant carotenoids such as β-carotene in yellow, red and green leafy vegetables, eg carrots, spinach, pumpkin, and in fruits such as mango. Vitamin A has physiological roles in vision as a component of rhodopsin in the rods of the retina and for gene expression and thereby normal tissue growth and differentiation.
Vitamin A measurement is used to diagnose suspected vitamin A deficiency or toxicity. Common indications for investigating vitamin A deficiency include malnutrition, for patients on long-term nutritional support such as total parental nutrition, and conditions associated with fat malabsorption including Cystic Fibrosis, pancreatic insufficiency and obstructive liver disease. Vitamin E is commonly requested alongside vitamin A in these patients. Deficiency may present as night blindness initially but can manifest as other ocular symptoms which can lead to loss of sight. Other manifestations of vitamin A deficiency include increased respiratory infections and diarrhoea.
Toxicity commonly occurs from either acute or chronic ingestion of preformed vitamin A. Clinical signs and symptoms of acute toxicity include raised intracranial pressure, headaches, nausea, vomiting and visual disturbances. Signs and symptoms of chronic toxicity include increased bone resorption, fractures and hepatoxicity. Synthetic retinoids are teratogenic and therefore vitamin A derived medications, products or medicines and the consumption of liver are contraindicated in pregnancy.
Retinol is bound to retinol binding protein (RBP) in the circulation. RBP decreases in the acute phase response. Consequently, vitamin A status is affected in the acute phase response/systemic inflammation with CRP concentrations of >10 mg/L and can cause a decrease in vitamin A results. Vitamin A should be rechecked when CRP is normalised where possible.
Sample requirements
Serum sample, centrifuged, separated and frozen within 24 hours of venepuncture.
Light protection not essential.
Minimum volume 0.5mL separated serum.
Haemolysed samples are not suitable for analysis.
Reference ranges
| Reference range µmol/L | |
| Age | Vitamin A |
| up to 1 year | 0.53 – 1.4 |
| 1-6 years | 0.7 – 1.5 |
| 7 – 12 years | 0.9 – 1.7 |
| 13 – 19 years | 0.9 – 2.5 |
| >20 years | 1.05 – 2.8 |
Storage and transport
Once centrifuged and separated, serum should be stored frozen at -20°C until dispatch.
Transport 1st class post ambient temperature
Delivery address
Central Pathology Reception
Clinical Blood Sciences
South West London Pathology
St Georges University Hospital Foundation NHS Trust
Ground Floor
Jenner Wing
Blackshaw Road
London
SW17 0QT
Contacts
Tony Dedman, Technical Lead for Specialist Biochemistry, Tony.dedman@stgeorges.nhs.uk
Clinical advice and result interpretation is available by contacting the duty biochemist at stgh-tr.DutyBiochemist@nhs.net.
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