|Clinical Use:||Testing Vitamin can diagnose Vitamin A deficiency and toxicity. It can also be used in monitoring levels in patients receiving Vitamin A medication.|
|Background:||The level of Vitamin A in the plasma or serum is a reflection of the quantities of Vitamin A and carotene (pro-vitamin A) ingested and absorbed by the intestine (carotene is converted to Vitamin A by intestinal absorptive cells and hepatocytes). Vitamin A plays an essential role in the function of the retina, is necessary for growth and differentiation of epithelial tissue, and is required for growth of bone, reproduction, and embryonic development. Together with certain carotenoids, Vitamin A enhances immune function, reducing the consequences of some infectious diseases.
Degenerative changes in eyes and skin are commonly observed in Vitamin A deficiency. Poor adaptation of vision to darkness (night blindness) is an early symptom that may be followed by degenerative changes in the retina. Severe or prolonged deficiency leads to dry eye (xerophthalmia) that can result in corneal ulcers, scarring, and blindness. Another important consequence of inadequate intake is acquired immunodeficiency disease (AIDS), where an increased incidence of death is associated with deficient Vitamin A levels. In patients with HIV, Vitamin A deficiency is associated with increased disease progression and mortality.
Chronic Vitamin A intoxication is a concern in normal adults who ingest >15 mg per day and children who ingest >6 mg per day of Vitamin A over a period of several months. Manifestations are various and include dry skin, cheilosis, glossitis, vomiting, alopecia, bone demineralization and pain, hypercalcemia, lymph node enlargement, hyperlipidemia, amenorrhea, and features of pseudotumor cerebri with increased intracranial pressure and papilledema. Liver fibrosis with portal hypertension may also result. Congenital malformations, like spontaneous abortions, craniofacial abnormalities, and valvular heart disease have been described in pregnant women taking Vitamin A in excess.
|Reference Ranges:||Adult: 1.3 – 2.9 µmol/L
5 – 10 years: 0.7 – 1.7 µmol/L
Up to 5 years: 0.5 – 1.7 µmol/L
|Patient Preparation:||None required|
|Specimen Requirements:||Serum (SST) OR plasma (Lithium Heparin)|
|Turnaround Time:||4 weeks|
|Referred Test:||Referred test|