3

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Getting ready for a blood test

Answered on August 19, 2014
Created October 08, 2010 at 2:50 AM

Hi all- I have a blood test scheduled for 9:30am Saturday morning and was wondering what an optimal amount of time to fast before the draw would be. I've heard 8 hours recommended for glucose testing and 12+ for lipid testing. I imagine that fasting for too long might cause my blood sugar to eventually rise above its baseline level and that there would also be a hormonal reaction to a long fast.

For what it's worth, I'm having the following tests done: comprehensive metabolic w/ eGFR (minerals and kidney/liver markers, I believe), lipids, CBC, C-reactive protein, TSH, free T4, free T3, free/total testosterone, D,25-OH.

Additionally, are there are any important considerations regarding what I eat for my last meal before the fast? Thanks in advance for any help!

3cb9200416c891365a5d0f3a9c7812c2

(90)

on October 09, 2010
at 05:23 PM

Thanks for your help. I went with 12.5 hours, and didn't mean to imply that I was trying to skew the results at all- I just wanted them to be maximally representative of my diet and lifestyle, with as little noise as possible.

0034e877123279fd4e16347f9829e514

on October 08, 2010
at 12:16 PM

Agreed twelve hours seems to be the most conservative for a full lipid panel.

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3 Answers

1
2b8c327d1296a96ad64cdadc7dffa72d

on October 08, 2010
at 05:37 AM

Your physician or the laboratory physician should tell you how long to fast. The best laboratory values will depend on the protocol for processing each test -- for example, no food after midnight is a typical protocol for an 8 am test, but your doc may tell you to FINISH your final meal by 8pm, so that digestion is complete by midnight, for example.

It may also be that your water intake may be restricted, so be sure to ask. And no mouthwash, no gum, no breath mints.

No exercise either.

If you have been low carbing (less than 50g/day) you may need to up those levels at least 3 days before the test, else your fasting glucose may give you a false reading.

1
5841391284e7af8c495c54bd90d3a795

(2764)

on October 08, 2010
at 05:36 AM

What did your doctor say when he ordered the test? You could call the blood lab and ask, too. I've always done at least 12 hours, sometimes more.

As for what to eat, I'd stick with your normal diet. I wouldn't want to slant the numbers one way or the other since I'd like to have good info rather than good numbers.

3cb9200416c891365a5d0f3a9c7812c2

(90)

on October 09, 2010
at 05:23 PM

Thanks for your help. I went with 12.5 hours, and didn't mean to imply that I was trying to skew the results at all- I just wanted them to be maximally representative of my diet and lifestyle, with as little noise as possible.

0034e877123279fd4e16347f9829e514

on October 08, 2010
at 12:16 PM

Agreed twelve hours seems to be the most conservative for a full lipid panel.

0
149af6e19a06675614dfbb6838a7d7c0

on October 08, 2010
at 12:23 PM

Here's a few more tests to consider

  1. Chemistry screen (electrolytes, liver enzymes, creatinine, glucose, bun, uric acid, triglycerides, cholesterol)
  2. Leptin, serum fasting
  3. Insulin, serum fasting, preferably via RIA
  4. Free T-3
  5. TSH
  6. Free IGF-1
  7. LDL size fractionation (VAP cholesterol)
  8. CRP high sensitivity
  9. Hbg-A1C
  10. Homocysteine: (May or may not need to be repeated after 1st follow-up depending on results)

Good luck and report back to us on the results...squeeze the ball...say ouch!

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