SIP

Subject Title: Clinical Chemistry
Name of Test: Total Carotene Test


Carotene is an orange photosynthetic pigment important for photosynthesis. The characteristic orange colour of carrots and red yellow pigments in fruits and vegetables are due to carotenoids. It comes in two primary forms; alpha-carotene and beta-carotene. Beta-carotene is probably the best known of them and is a precursor of Vitamin A. Carotene is stored in the liver and converted to Vitamin A as needed. In addition, carotene is an antioxidant nutrient so it can reduce the risks of cardiovascular diseases and some forms of cancer.


Principle and Procedure of Test
In this test, protein are first removed by precipitation with ethanol. The carotene and other form of carotenoids are extracted with petroleum ether. The characteristics absorbance is measured at 450nm.

Before running the patient sample, two levels of controls are run. Calculations are done to obtain the concentration of carotene. After ensuring that the QC results are acceptable, we will run the patient sample.
1) Pipette 1mL of patient serum sample into the glass test-tube

2) Add 1ml of absolute ethanol into the glass test-tube

3) Vortex the glass test-tube

4) Add 2ml of petroleum ether and vortex them for 10 min to ensure they are well mixed

5) Allow the glass test-tube to stand for 5min

6) After 5 min, extract the top layer of ether and transfer them into the glass microcurvette until it is filled to the top for absorbance readings. This is to enable complete light transmission through the solution

7) Using petroleum ether as blank, place the glass microcurvette into the spectrometer. Check for turbidity in the sample as it can cause false high absorbance readings

8) The absorbance is measured at 450nm

9) Calculations are done to obtain the concentration of carotene. This is as follow:

ODdiff X 14.59 = ____µmol/L

*Note: ODdiff = OD (450nm) – OD blank


Reference Range: 0.93 to 3.73µmol/L


Clinical Interpretation
Concentrations above the reference range shows a high levels of carotene in the body known as carotenemia. Unlike excess Vitamin A, excess carotene is non-toxic. Although carotenemia is not dangerous, it can lead to yellowish/orange discolouration of the skin, mostly occurring in the palms of hands and the soles of the feet. This is due to the consumption of abundance carotene from foods (such as carrot juice) or from supplements. It is nearly impossible to overdose on carotene because the body excretes the excess. This can also be a medical sign of other conditions such as renal diseases. Since carotene itself is harmless, it does not require treatment. Reducing high quantities intake of carotene will gradually remove the colourisation of skin. Sometimes yellowish discolouration of the skin can be misdiagnosed as jaundice. Jaundice affects the colour of the eye while carotenemia does not. A bilirubin serum test can be used to identify whether jaundice is involved.

Concentrations below the reference range shows there is carotene deficiency. Such deficiencies are seldom seen, however, even in people who don't eat fruits or vegetables or take supplements, because so many other foods supply the nutrient. Symptoms of carotene deficiency include dry skin, night blindness and susceptibility to infection.

Total carotene test is a valuable part of diagnosis of Vitamin A deficiency or excessive Vitamin A. This is because carotene is converted to Vitamin A in the body. However, the actual diagnosis requires interpretation of test result in conjunction with other clinical findings.


Soong Ci Liang
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