Exceptions to Fasting for Laboratory Blood Tests?

Okay… so my other question is… if you have Dawn Phenomenon (whether it’s first wave, or two waves of it)… do you still keep your fast for the next morning blood work, or do you have your snacks as usual? And if you have a low, do you have your snack, and continue with your blood work, or do you reschedule and try to pull it off, again, at some other point?

You are supposed to fast for the fasting glucose test. This does make you wonder whether the guidelines on diagnosis and treatment targets are for morning fasting numbers or not. I’ve never gotten a clear answer, even from endos. I’ve chosen to interpret the diagnosis and treatment targets as being specifically about morning fasting. You are diabetic if your ‘morning’ fasting is > 126 mg/dl and you are properly controlled if your ‘morning’ fasting is < 110 mg/dl. Needless to say, I am not yet properly controlled.

What makes it even stranger is that my routine is to have a protein shake upon rising. If I have the shake, my DP is arrested, if I don’t my blood sugar may continue rising. Not eating actually makes it worse.

I guess it just begs the question for me, because there is no other treatment for Dawn Phenomenon than to have a snack right at bed time, or maybe exercising closer to bed time (which is not good for some Diabetics)… So fasting BG would always be above that 126…

I would interpret fasting to be 8-12 hours without food regardless of the time of day. If you have issues with DP perhaps your lab work could be taken later in the day. The reason that most fasting lab work is done in the morning is because of convenience for the patient (its easier to fast while sleeping than while up and about) not because there is any special significance to morning values.

That said, there are certain labs that should be done in the A.M (cortisol for example) because these values have normal, physiologic diurnal variation, but FBG can be tested at anytime during the day if the only value you are interested in is the BG in the absence of food.

I also believe that we will see a trend away from FBG and OGT testing as A1c becomes more easily and widely available. It is well known that the single point in time glucose reading (fasting or not) is generally of little value. Your FBG on any given day may vary and the impact on long term complications and control is much better indicated by A1c. There are exceptions, of course, where FGB and glucose tolerance will still need to be used.

So after all that, I think my comment to your question is that if you have issues with DP then your FBG readings in the morning need to be interpreted in that context by the physician, or FBG should be evaluated at a different time during the day. Snacking before a FBG test negates the usefulness of the test.

When I have an order for fasting( 12 hours ) , it is related to the Cholesterol test , not the diabetes. Lab tech asks , if I had anything to drink , except H2O ,or eat in the last 12 hours …if yes, test is postponed .I once drank tea within those 12 hours and sent home …a good learning experience .
As a pumper , I set a temp . basal and it does really not matter, if the BG number is higher than usual .The reason for a fast needs to be clarified here.Hope I understood your question .

bsc, this is a good point. I understand why the endos would have differing opinions. In someways, FBG is fasting whether it is morning or not, but on the other hand the variation in BG throughout the day may or may not be affected by a variety hormonal factors. My interpretation is that it really depends on just how much value you place on the FBG reading to begin with. In my practice, I would always interpret the FBG in an individual context and in conjunction with other labs (including A1c).

That’s a very good point, Tim… If I get ordered just a simple A1c and FBG, I’ll postpone it to later in the day… But if, as so helpfully pointed out by nel, below, it is a test that includes cholesterol, and other tests, I’ll try not to worry so much about it. :slight_smile:

The only real value on lipid panels that is affected by fasting are the triglycerides, so if you ever get non-fasting labs it’s good to note. Personally, I never get my labs drawn fasting unless I’m testing for something more sensitive (eg, PTH and Calcium levels). The affect on lipids is “generally” minor.