Eating Cooked Meat Can Distort CKD Stage in Diabetes

Miriam E. Tucker

October 02, 2013

Eating cooked meat can raise serum creatinine significantly enough to drop the estimated glomerular filtration rate (eGFR) calculation and in some cases lead to a misclassification of chronic kidney disease (CKD) stage in patients with diabetes, a new prospective study has found.

The cooking process converts creatine to creatinine in meat, which in turn transiently increases the diner's serum creatinine. Fasting is not routinely recommended for renal-function tests, but these results suggest that it should be or, at the very least, that patients should avoid eating cooked meat before undergoing such tests, say Sunil Nair, MRCP, from the University Hospital Aintree, Liverpool, United Kingdom, and colleagues in their paper published online September 23 in Diabetes Care.

The message "is that serum creatinine and eGFR should not be considered absolute values, and there are several factors that introduce variability in their measurement," Dr. Nair told Medscape Medical News.

The findings have numerous clinical implications, since eGFR thresholds are the basis for starting and stopping certain medications and for performing expensive tests, he and his colleagues note.

Cooked Meat's Effect Is Significant but Transient

The researchers explain that diabetic nephropathy is a leading cause of end-stage renal disease (ESRD) and that accurate screening and staging of CKD is essential for timely intervention as recommended by national and international guidelines and to guide dose adjustment of other medicines. Glomerular filtration rate (GFR) is recognized as the best measure of kidney function in health and disease, and the easiest way to assess it is to estimate it based on serum creatinine and other variables such as age, gender, race, and body size.

Dr. Nair and colleagues studied 64 adult patients with type 1 (14%) or type 2 diabetes (86%) and chronic kidney disease, with 16 in each of 4 CKD stage groups: 1 and 2, 3a, 3b, and 4. A group of 16 healthy volunteers was also studied, for a total of 80 subjects.

Subjects were given 1 of 2 meals, each containing about 44 g of protein: One consisted of 2 grilled quarter-pound beef burgers, the other 2 grilled vegetarian burgers. Both meals also included 2 buns, a vegetable salad, and 250 mL of water.

Blood samples were taken before the meal (fasting) and at 1, 2, and 4 hours after. Blood samples were also taken the morning after the meal following a 12-hour overnight fast.

Significant differences in serum creatinine and eGFR were seen following the meat meal in the healthy volunteers and the patients with CKD. The maximum rise in creatinine occurred at 2 hours after eating for the healthy volunteers and those with CKD stages 1 and 2, whereas for CKD 3a and 3b the maximum rise was seen at 4 hours postprandially and in CKD 4 the 4-hour creatinine was just 0.5 µ mol/L lower than the 2-hour value.

With the cooked-meat meal, the changes in both serum creatinine and eGFR from baseline to 2 hours achieved significance of P < .01 for the healthy volunteers and those in CKD stages 1 and 2, 3b, and 4, while for CKD stage 3a the significance was even greater, with P < .001.

As a result of the meat consumption, the median eGFR in the CKD 3a group fell from 52 to 45.2 mL/min/1.73 m2 at 2 hours, dropping further to 42.8 mL/min/1.73 m2 at 4 hours, shifting 6 of those 16 patients into the CKD 3b category, the doctors report.

In contrast, there were no significant differences in serum creatinine or eGFR at any point within 4 hours after the nonmeat meal in any of the participants. Nor were there any changes the following morning (12 hours) after either the meat or nonmeat meal.

Numerous Clinical Implications

Dr. Nair told Medscape Medical News there are important clinical implications for the management of diabetes patients. For example, recommendations call for reducing the dose of metformin when eGFR falls below 40 mL/min/1.73 m2 and for stopping the medication if eGFR drops below 30 mL/min/1.73 m2. Similarly, recommendations for limiting use of glucagonlike peptide-1 (GLP-1) agonist drugs are based on eGFR cutoffs varying from 30 to 60 mL/min/1.73 m2.

What's more, he said, overestimation of creatinine and underestimation of eGFR could result in unnecessary hospital admission. For instance, patients undergoing coronary angiograms are recommended to receive prehydration and drugs such as N-acetyl cysteine or bicarbonates if eGFR is below 60 mL/min/1.73 m2.

Although the investigators recommend that the solution to this problem is to simply ask patients to come to the lab in a fasting state, he acknowledged that "from a clinical perspective, there will be a risk of hypoglycemia in insulin-treated patients." Therefore, since the effect on creatinine appears to be limited to consumption of cooked-meat protein, "the recommendation could be modified to [merely] avoiding cooked meat prior to blood sampling to measure renal function."

Dr. Nair said the same effect would be expected with meat from all vertebrates, including chicken, but that "we do not have a lot of specific evidence about fish."

And he said his future work could circumvent the problem: "I plan to study the potential use of other markers of renal function such as cystatin-C, which is not known to be affected by protein consumption or obesity."

The authors have reported no relevant financial relationships, and no external funding was obtained for this study.

Diabetes Care. Published online September 23, 2013. Abstract

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