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What is Vitamin C test?

Vitamin C or ascorbic acid test is used to check the levels of vitamin C in blood. Ascorbic acid is a water-soluble vitamin which is present in abundant amounts in citrus fruits such as oranges, lemons, kiwi and grapefruit, and vegetables. It performs various important functions in the body:

  • Being a natural antioxidant, it helps to protect body cells from free radical damage and oxidative stress. Free radicals are singlet oxygen at are produced as a result of various metabolic processes and lead to gradual deterioration of normal body functions
  • Vitamin C promotes the synthesis of collagen, a protein that helps in wound healing 
  • It also increases iron absorption from foods and supports the immune system by protecting the person against several diseases
  • It is known that vitamin C helps in preventing several types of cancers and decreases the risk of cardiovascular diseases
  • Furthermore, it helps in tissue and drug metabolism and decelerates the ageing process, which makes one look younger
  1. Why is Vitamin C test performed?
  2. How do you prepare for Vitamin C test?
  3. How is Vitamin C test prformed?
  4. Vitamin C test results and normal range

Vitamin C blood test checks if the person has normal values of the vitamin in their body. It s is mainly used in the diagnosis of scurvy.

This test is also recommended to people who experience symptoms such as:

Also, a vitamin C test is advised to people who are undergoing treatment for vitamin C deficiency. In this case, the test helps check the effectiveness of the therapy as well as current vitamin C levels in the body. 

If a person with scurvy or malnutrition visits a hospital for a general check-up, vitamin C test might be advised to assess the status of the disease. More often than not, this test is ordered with other vitamin tests for confirmation of the diagnosis.

Overnight fasting is generally recommended before the test. Make sure to inform your doctor if you are suffering from any medical conditions and allergies or are taking any medications. A doctor will give specific instructions on a case-to-case basis. If you are taking vitamin C supplements, your doctor might ask you to discontinue them before the test.

  • A laboratory assistant will first observe your arm to look for a suitable vein to puncture 
  • If needed, a tourniquet will be tied onto your arm to make the vein more visible
  • The skin above the vein would be cleaned with an antiseptic solution
  • A blood sample will be drawn using a sterile needle and syringe. You may feel a slight prick during this procedure
  • The blood will then be transferred to a collection tube, which is labelled and taken to a laboratory for further analysis

After the test, you will be asked to apply slight pressure to the puncture site and dressing is done to prevent infection. You will be allowed to go home immediately after the test.

Normal results:

Normal concentration of vitamin C in plasma ranges between 6.3–14 mg/L.

Abnormal results:

Increased levels of vitamin C can be due to the following:

  • Reduced effect of anticoagulants
  • Diarrhoea
  • Overabsorption of iron
  • Supplements for diabetes
  • Nausea
  • History of kidney stones: Persons with a history of kidney stones are at an increased risk of developing oxalate stones due to high intake of vitamin C in their diet

Reduced levels of vitamin C can be due to the following:

Vitamin C levels in tissues and fluids are consistently higher in women as compared to men. Plasma values are a better indicator of recent intake of vitamin C. 

Vitamin C levels in white cells are suggestive of its storage in the cellular and body pool. Vitamin C levels in the saliva are not very consistent. 

Results of vitamin C test in urine are not useful, especially in persons with higher concentrations of ascorbic acid as it may lead to false-negative results.

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.


  1. John Edward Hall, Arthur C. Guyton. Guyton and Hall Textbook of Medical Physiology. Saunders/Elsevier, 2011; ISBN 0808924001, 9780808924005
  2. Juanita Watson, Marie S. Jaffe, June H. Cella. Nurse's manual of laboratory and diagnostic tests. F.A. Davis,1995; ISBN; 0803691017, 9780803691018
  3. Frances Talaska Fischbach, Marshall Barnett. A Manual of Laboratory and Diagnostic Tests. McGraw-Hill Education; Medical; 1 edition (October 29, 2007); ISBN-10: 0071481524
  4. BMJ Best Practice. Vitamin C deficiency. BMJ Publishing Group [Internet]
  5. Joël Pincemail et al. Lifestyle Behaviours and Plasma Vitamin C and Beta-Carotene Levels from the ELAN Population (Liège, Belgium). Journal of Nutrition and Metabolism Volume 2011, Article ID 494370, 10 pages
  6. Nagel D et al. Investigations of ascorbic acid interference in urine test strips. Clin Lab. 2006;52(3-4):149-53. PMID: 16584061
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