Tuesday 22 January 2013

Fasting for cholesterol test is not absolutely necessary - more evidence



Image source: Neeta Lind - cc




My previous post discussed about a recent study showing that fasting is usually not necessary for cholesterol test. To further strengthen this argument, here is another older study to support this.



Langstead and coauthors published this study in the journal Circulation 2008.

They conducted a cross-sectional study inclduing 33,391 individuals (Age 20 - 95 years old). Study participants were given self-administered questionnaire on detailed medical history and their lifestyle. These questionnaires were then checked by an examiner on the day of attendance. All study participants had blood test done for cholesterols. Prior to the blood test, they were asked about the last time they had a meal, and these were categorized into: 0 to 1, 1 to 2, 2 to 3, 3 to 4, 4 to 5, 5 to 6, 6 to 7, 7 to 8, or 8 hours ago ( = fasting).

The cholesterol tested include:
  • Total cholesterol (TC)
  • High-density lipoprotein cholesterol (HDL) - aka "Good" cholesterol
  • Low-density lipoprotein cholesterol (LDL) - aka "Bad" cholesterol
  • Triglycerides (TG)
  • Apolipoprotein A1
  • Apolipoprotein B

Interestingly, TC, LDL, HDL were reduced up to 3-5 hours after the last meal. TG increased up to 6 hours after the last meal. Non-HDL cholesterol level, apolipoprotein A1 level, apolipoprotein B level, ratio of TC to HDL, and ratio of apolipoprotein B to apolipoprotein A1 did not change in response to normal food intake.

The maximum changes after normal food and fluid intake from fasting levels were:

  • TC:  0.2 mmol/L (7.73mg/dl)
  • LDL: 0.2 mmol/L (7.73mg/dl)
  • HDL: 0.1 mmol/L (3.87mg/dl)
  • TG: 0.3 mmol/L (26.57mg/dl)


To put things in perspective, let's look at the recommended level for cholesterol. According to the ATP 3 (Adult Treatment Panel) guideline, the primary target for treatment is the bad cholesterol LDL, which should be less than: 100mg/dl (2.6mmol/l), 130mg/dl (3.4mmol/l), or 160mg/dl (4.1mmol/l), depending on how many cardiovascular risk factors a person has. So if you have no risk factors (hence target LDL <160mg/dl or 4.1mmol/l), and your NON-fasting LDL is 135mg/dl (3.5mmol/l), then you are well below the target range, even accounting for the 0.2 mmol/L (7.73mg/dl) variation observed in the study, and therefore a fasting test is not required.

As you can see, while the cholesterol levels varied in the period after food intake, the variation is of such small extent that it usually doesn't matter.

In summary: This study again reinforced that, for most of us, fasting for cholesterol test is an unnecessary hassle. The only time that fasting test is really required is when your results are on the borderline of the recommended level, and in particular if the decision of commencing medication needs to be made.




Summary of the study 



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