CHEMISTRY - Measuring Cholesterol

Dear Medical Technologists, I'm going to share with you one of the point-of-care testing system that I've learnt when I was sent out for an Outreach Program few weeks ago. This is regarding cholesterol measurement using the Accutrend® GCT Meter (Roche).

Name of Test: Cholesterol (CHOL) Measurement using Accutrend® GCT Meter

(Picture taken from Divant.com)

Introduction:

Cholesterol is a major steroid in human body. Majority is free, unesterified, that form the structural component of the cell membrane. Its content in the body is dependent on the diet, synthesis within tissue cells and excretion by the liver. Proportion absorbed in the intestine is affected by the amount ingested, with less absorbance when intake is high.

Cholesterol is insoluble in water, thus before being absorbed, unesterified cholesterol is first solublized. It is excreted unchanged or as bile acids in bile. Transportation in plasma and its metabolism are related to lipoprotien metabolism. 2/3 of the plasma cholesterol is in the esterified form.


Materials

• Accutrend® GCT Meter



• Accu-Chek Safe-T-Pro Plus® lancet device
  
  
  

(Picture taken from: Accu-Chek.ca)


• Cholesterol Test Strip



• Code Strip (found in every new pack of test strips, for calibration purpose)



• Control CH1 (for QC purpose)



• Alcohol Swab



• Cotton ball

Procedure (from finger-prick to measurement):

• Switch on the Accutrend® GCT Meter and insert the test strip



• Tally the participant's name with the LIS



• Select the depth of the Accu-Chek Safe-T-Pro Plus® lancet device and the puncture site



• Clean the puncture site with alcohol swab



• Twist off the sterility cap and gently press the lancet against the side of the finger tip



• Apply a hanging drop of blood to the yellow test field on top of the test strip



• Close the meter flap immediately and wait for 180s countdown



• Stop the bleed using a cotton ball



• Read measurement



• Enter into LIS

Principle of Analysis: Reflectance Photometry

The yellow region of each test strip contains detection reagent which reacts with the blood and causes a colour change. The meter measures the intensity of the reaction colour based on reflectance photometry and calculates the concentration of the sample through a "lot-specific" algorithm (i.e. the data previously entered by mean of code strip), giving the cholesterol reading.

Test Results:

Range: 3.88 - 7.76mmol/L

LO indicates value is below 3.88; HI indicates value is above 7.76

In either cases, turn the strip over and check if the test region is uniformly covered by the blood. If partially coloured, repeat test.

Desirable: < 5.12 mmol/L
Borderline High: 5.12 - 6.18 mmol/L
High: > 6.18 mmol/L

Advantages:

• Can be performed on non-fasting individual's blood



• Uses dry chemistry methodology outside a lab setting (suitable for Public screening)



• Low cost



• Convenient; Portability



• Fast results (within 180s)



• Minimal blood for testing (requires only 1 drop)



• Easy to operate for the medical worker



• Gives a relatively accurate result
  

Disadvantages:

Test is affacted by...

• IV infusion of Vitamin C



• Elevated bilirubin (>171umol/L); Jaundice



• Haematocrit > 55%



• Methylaminoantiprine



• Gentisic Acid
  

Clinical Significance:

There is a good correlation between cholesterol level and incidence of coronary artery diseases. Hence, by offering this fast and convenient point-of-care testing, any risk of atherosclerosis can be detected early. However, further investigation is required to justify the finding.

Questions for me???


PEI SHAN, TG02