What Is Maximum Time Your Can Fast For Bloodwork?

[GeoGeo]

What is the maximum time you can fast for bloodwork? Is 16 hours too long? Have to be done eating by 4 p.m. due to medical reason and then the lab doesn't open up until 7:30 a.m. I noticed my cholesterol readings were excellent and assumed I had fasted too long. And are there any labs that open earlier or offer 24 hour service?

[jimbo2012]

This says 12 hours :22yikes:

How Long to Fast Before a Blood Test (http://www.buzzle.com/articles/how-long-to-fast-before-a-blood-test.html)

[blueash]

To your specific question of fasting and your lipid results

Fasting and Nonfasting Lipid Levels (http://circ.ahajournals.org/content/118/20/2047.short)

http://circ.ahajournals.org/content/118/10/993.short


Conclusion Fasting for routine lipid level determinations is largely unnecessary and unlikely to affect patient clinical risk stratification, while nonfasting measurement might improve patient compliance and safety.

Blood cholesterol screening influence of fasting state on cholester... - PubMed - NCBI (http://www.ncbi.nlm.nih.gov/pubmed/10886474) for an additional source

And here is a study suggesting that Non-fasting triglycerides in women is a better test than fasting triglycerides when used for predicting cardiac events JAMA Network | JAMA | Fasting Compared With Nonfasting Triglycerides and Risk of Cardiovascular Events in Women (http://jama.jamanetwork.com/article.aspx?articleid=208018)

Now this is standard of care, but fasting only modifies the triglyceride and LDL-Calculated. LDL if measured directly is not altered by fasting. However the older lab tests did not measure LDL directly but rather used a formula where the directly measured total, HDL and triglycerides were used to calculate LDL. As triglycerides are altered by fasting this old indirect method did require fasting.

So if you had good lipids after a 16 hr fast, they should also have been good after a 12 hour or a zero hour fast. There is no "too long" in lipid testing except that if you fast for an extended period, then eat, then measure your triglycerides, the increase after a fast will be more than the increase after a usual spacing of meals.

Suggestion: If fasting is difficult then inform your doctor that you would like to have your lipids tested in a non-fasting manner.

The latest criteria for who and what to screen is here:
http://www.ahrq.gov/professionals/clinicians-providers/guidelines-recommendations/guide/section2c.html

"The preferred screening tests for dyslipidemia are measuring serum lipid (total cholesterol, high-density and low-density lipoprotein cholesterol) levels in non-fasting or fasting samples. Abnormal screening results should be confirmed by a repeated sample on a separate occasion, and the average of both results should be used for risk assessment.
Timing of Screening
The optimal interval for screening is uncertain. Reasonable options include every 5 years, shorter intervals for people who have lipid levels close to those warranting therapy, and longer intervals for those not at increased risk who have had repeatedly normal lipid levels.

An age at which to stop screening has not been established. Screening may be appropriate in older people who have never been screened; repeated screening is less important in older people because lipid levels are less likely to increase after age 65 years."

[2BNTV]

16 hours seems a little too long to be fasting. I was told 10 hours minimum, by the lab people, but I would ask my doctor, as you don't want or need incorrect results. IMHO

[jnieman]

Stay hydrated

[Nursebarb1]

blueash: Very good information. Thank you and I concur with your findings. If only the medical community were more up to speed.