Do Patients With Diabetes Need to Fast for Lipid Tests?

Miriam E Tucker

November 05, 2014

Should patients with diabetes be required to fast for lipid tests? No, say the authors of a review article published in the November issue of Postgraduate Medicine.

Others disagree, however, and debate on the topic is heating up.

"We would like doctors who treat patients with diabetes to ask, 'Do I really need to fast my patient for this test?' There is now strong and compelling evidence that in the case of the lipid-profile [test] perhaps we don't need to fast our patients," lead author of the new paper, Dr Saleh Aldasouqi ( Michigan State University College of Human Medicine, East Lansing) told Medscape Medical News.

Dr Aldasouqi and coauthor Dr George Grunberger (Grunberger Diabetes Institute, Bloomfield Hills, MI), who is incoming president of the American Association of Clinical Endocrinologists, present a number of arguments in their article as to why they think fasting is no longer necessary.

They point to recent evidence suggesting there is little difference in LDL-cholesterol levels between tests done in fasted vs nonfasted states and say that the two testing modes equally predict mortality. In addition, capturing postprandial triglyceride spikes may actually better predict cardiovascular risk, they add.

Moreover, they say, fasting is inconvenient and can even be dangerous, because of the risk for hypoglycemia in patients with type 1 diabetes and in those with type 2 diabetes who use insulin or sulfonylureas (Diabetes Care. 2011;34:e52).

But on the other side of the debate are experts who argue that the entire literature addressing the link between lipid levels and cardiovascular risk is based on fasted values.

There aren't yet enough data linking nonfasting values to cardiovascular outcomes to support changing practice, they argue. Moreover, doing so would introduce further variability than exists already and an unacceptable lack of standardization.

More Data Needed to Support Shift Away From Fasting Values

One of those who doesn't see the need for change is Dr Samuel E Dagogo-Jack (division of endocrinology, diabetes, and metabolism, and director, Clinical Research Center, University of Tennessee Health Science Center, Memphis), who is the incoming president, medicine and science, of the American Diabetes Association.

"People are used to measuring many things in the fasted state," he told Medscape Medical News. "To superimpose an additional uncontrollable measure of random dietary patterns is going to make interpretation exceedingly difficult."

And Dr Robert H Eckel (University of Colorado, Denver), believes that more data are needed to support a universal shift away from fasting for lipid tests.

"The bottom line is, all of the guideline updates are based on fasting lipids," said Dr Eckel, a coauthor on the 2013 American Heart Association/American College of Cardiology guideline on the treatment of blood cholesterol to reduce atherosclerotic cardiovascular risk in adults.

"We were puristic in the approach to the cholesterol guidelines, and those are fasted values. I think it would require a substantial database going forward in patients with and without diabetes to indicate that nonfasted is equally predictive. I just don't think we have enough."

Dr Aldasouqi told Medscape Medical News that nonfasting lipid tests can be interpreted in a number of ways.

Food will raise triglyceride levels by 20% to 50%, which will result in about a 10% lower calculated LDL using the Friedewald equation (LDL = total cholesterol – [HDL + 1/5 of triglycerides]).

To account for this, 10% can be added to the calculated LDL result for a nonfasted test. (The equation doesn't work if the triglycerides are above 400 mg/dL, however.)

Alternatively, one can just use non-HDL (total cholesterol – HDL) for both diagnostic and therapeutic purposes, with a treatment target of 30 mg/dL higher than the published LDL target value.

Direct measurement of LDL cholesterol and measurement of lipoprotein subclass profiles by nuclear magnetic resonance spectroscopy are also options that can be done fasted or nonfasted, although these tests are more expensive and therefore used less frequently, he noted.

Educate Diabetes Patients About Fasting; Keep Fast Brief

Dr Dagogo-Jack is keen to stress, however, that physicians and other practitioners "should pay extreme attention to their diabetic patients who are required to undergo any testing that requires fasting. The test needs to be scheduled as humanely and conveniently as possible. Namely, the fast should be as brief as is necessary for the test."

Diabetes patients who take insulin or sulfonylureas need to be educated about holding their morning doses and possibly bringing along breakfast or a snack to eat immediately after the test, he says.

Drs Aldasouqi and Grunberger agree, adding that — when fasting is deemed to be necessary — patients should also be educated about cutting back the basal insulin dose the night before by a third and monitoring glucose levels more frequently.

These measures, they say, are important for preventing a phenomenon thus far described anecdotally and in case series as "fasting-evoked en-route hypoglycemia in diabetes [FEEHD]," which could place patients at risk for car accidents they are while driving to the lab (Postgrad Med. 2013;125:136-143.)

While there are currently guidelines in the literature addressing management of diabetes medications for other situations that involve fasting, such as surgical procedures or religious observance, there are no such recommendations for laboratory tests. However, patients are very likely to be driving themselves to lab tests and might not have someone else with them in the car, Dr Aldasouqi noted.

"I'm not arguing we should eliminate fasting altogether. We're still not yet there. But if you think your patient needs to be fasting, then prepare the patient for fasting. Give them instructions," he told Medscape Medical News.

Rates of FEEHD are unknown and likely underreported, he and Dr Grunberger write.

They are currently enrolling insulin- and sulfonylurea-using patients in a four-site survey that will ask about hypoglycemia in general and during fasting for lab tests in particular. "We are expecting to find that a significant proportion of patients [experience FEEHD]," Dr. Aldasouqi said.

Dr Eckel said, "The risk of hypoglycemia is real….In a patient at risk for hypoglycemia — either type 1 or type 2 on basal-bolus insulin — a nonfasted value is perfectly acceptable and can be used to assess risk."

"Knowledge Is Constantly Evolving"

Dr. Eckel also believes, for his part, that practice might shift eventually.

"I understand all of the arguments for nonfasting, and I think in 10 or 20 years the field should move in that direction because I'm convinced that the nonfasted patient with nonfasting labs can be as valuable — and potentially more valuable — than the fasted patient because it's more realistic, more real-time."

The evolution probably won't be straightforward, though. "I think there have to be more data to suggest nonfasting is perfectly acceptable in predicting risk. But are people going to repeat all the statin trials? Probably not….It's unlikely this will be evidence-based, but it may become practically based."

With regard to the American Diabetes Association — which still recommends fasted lipid testing although it does include a caution about hypoglycemia — Dr Dagogo-Jack said that this may be a similar situation to the use of HbA1c for diabetes diagnosis, a practice ADA resisted for a long time before finally recommending it in 2009.

"Knowledge is constantly evolving….We can never close the door. We need more data, more rigorous testing across all demographic groups and all risk groups, and most important, we need prognostic information."

However, he added, "The ADA is moving away from a prescriptive formula for managing the 29.1 million people with diabetes in the country to a more individualized and nuanced approach, where the physician and the patient have a dialog and discuss the various options."

Dr Aldasouqi is a presenter for Takeda, Janssen, and Sanofi. Dr Grunberger is a presenter for Lilly, Novo Nordisk, Bristol-Myers Squibb, Valeritas, Takeda, Merck, Boehringer Ingelheim, Sanofi, and Janssen. He has also received research funding from Lilly, Novo Nordisk, and Bristol-Myers Squibb. Dr Dagogo-Jack has served as consultant or advisory board member for Merck, Novo Nordisk, and Eli Lilly. Dr. Eckel has reported that he has no relevant financial relationships.

Postgrad Med. 2014;126: DOI: 10.3810/pgm.2014.11.2837. Abstract

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