Vitamin A test: normal range and what the result means

Vitamin A is a fat-soluble vitamin that the body does not make on its own — we get it from animal foods (in the form of retinol) or from plant foods containing beta-carotene, which the body then converts into retinol. It is needed by the cells of the retina that detect light, which is why a shortage of vitamin A shows up first as poor adaptation to the dark. Vitamin A also matters for the integrity of the skin and mucous membranes, for the working of the immune system, and for cell growth and division. The blood test measures the amount of retinol (or total vitamin A) in serum and is most often ordered when a deficiency is suspected or, conversely, an excess. Because vitamin A is fat-soluble, it builds up in the liver and can cause poisoning when supplement doses are too high. The test is not a routine part of a complete blood count — it is usually requested specifically, when there are particular symptoms or risk factors.

• When vitamin A deficiency is suspected — worsening adaptation to the dark or night blindness
• With recurrent infections, or skin that is dry and heals poorly
• In children, when there are signs of a growth problem or of an eye condition
• When vitamin A excess is suspected — watching for headache, bone or muscle pain, double vision
• In illnesses that interfere with fat absorption (for example bowel or pancreatic disease), where there is a risk of deficiency
• When taking high-dose vitamin A supplements — to watch for a possible excess

A raised vitamin A level in blood is treated as an excess, per the MedlinePlus encyclopedia, when it goes above 4.2 µmol/l. Vitamin A is fat-soluble and builds up in the liver, so an excess is most often connected with taking too much in supplements rather than with diet. Possible symptoms are anaemia, bone and muscle pain, diarrhoea, double vision, hair loss, increased pressure in the brain, problems with muscle coordination, an enlarged liver or spleen, and nausea.

Causes listed for a high result:

• Taking too much vitamin A in supplements
• Too much retinol in food (for example a lot of liver in the diet)
• Liver disease that interferes with clearing vitamin A from the body

What is usually looked at after a high result:

• Which supplements are being taken and at what doses — worth discussing with your doctor
• Liver markers, since vitamin A builds up in the liver
• Whether supplements need to be stopped or reduced
• When to repeat the test to assess the change

A lowered vitamin A level is treated as a deficiency, per the MedlinePlus encyclopedia, when the value is below 1.1 µmol/l. A deficiency is most often linked to an inadequate diet or to problems absorbing fat. Possible symptoms are bones or teeth that do not develop properly, inflammation of the eyes, irritability, hair loss, loss of appetite, night blindness, recurrent infections and skin rashes.

Causes listed for a low result:

• Too little vitamin A in food
• Problems absorbing fat (for example bowel or pancreatic disease)
• Liver disease that interferes with storing and using vitamin A

What is usually looked at after a low result:

• Diet, and conditions that interfere with fat absorption
• Whether there are signs of other vitamin deficiencies (for example E or D), since these are fat-soluble too
• An assessment of vision, especially adaptation to the dark
• When to repeat the test to assess the change