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Laboratory data evaluation: how does the renal dietitian interpret results?

As a preceptor for an internship program, I am frequently asked what it takes to be a renal dietitian (RD). In short, I respond by saying you have to have a love of chronic care, desire to be a team player, and a passion for medical related puzzles. The inevitable question is, why puzzles? Understanding each laboratory result and its desired value is important, but how it all fits together is what really matters. The renal diet requires so many considerations that without a wide array of lab values, the RD would be unable to assess the nutritional status of a patient and provide the appropriate advice in regards to the renal diet.

Since the kidneys are the master chemists of the body, the ultimate goal is striking a balance between sustaining life and maintaining a desirable quality of life. To accomplish this, a considerable amount of blood is drawn from dialysis patients. The bulk of a patient's blood work is drawn at a specified time each month mad there in lies the cornerstone of the dietitian's role on the renal team.

Food-Related Labs

Some labs directly reflect a patient's specific food intake. These can be frustrating for the patient, as no one likes to be "caught" with their hand in the cookie jar.

Potassium. Education regarding foods high in potassium and the consequences of hyperkalemia are provided to each patient. Given the potentially grave consequences of hyperkalemia, patients generally avoid high potassium foods. Seasonal variation of intake seems to influence this value the most (i.e., melons in the summer, tomatoes toward fall, etc.), thus periodic reinforcement of the guidelines are necessary. Fluctuations in appetite result ill changes in potassium intake, which may require dialysate changes. There are however, a number of nondietary issues associated with hyperkalemia, where treatment of the underlying cause corrects the hyperkalemia. These include hemolysis, high blood glucose values, poorly functioning access, drug interactions, catabolism, and constipation (McCann, 2002).

Calcium, phosphorus, and PTH. Maintenance of desired values is essential to prevent renal bone disease and soft tissue calcification. There are a number of foods that can precipitate hyperphosphatemia, but perhaps a more likely culprit is the patient's use of binders. Failing to take binders as prescribed due to cost or side effects are common reasons, but the possibility of a mismatch of binders and food must be considered. Dietitians can help patients properly distribute their binders throughout the day. Failure to do so can lead to hypercalcemia (with calcium based binders) and/or hyperphosphatemia. Often, provision of a specific strategy for taking binders is required, as it can be difficult for patients to remember to take them. The type of binder and need for vitamin D, as well as dosing requirements, are based on these lab value results.

Albumin. The albumin level is reflective of protein intake, but must not be considered the sole marker of nutritional status. When serum levels are low, efforts are made to increase the patient's protein intake via diet modification and use of nutritional supplements. Despite improvement in protein intake, some patients will persistently have low albumin levels and another etiology must be sought. Research is now available regarding the fact that perhaps a low albumin level is a maker of inflammation, which is associated with a high percentage of morbidity and mortality, rather than nutritional status. When factors beyond nutrition are in question, a measured Creactive protein (CRP) level can be helpful to rule out inflammation.

Markers of Nutritional Status

Some labs, when observed over time, will provide a glimpse into the nutritional status of a dialysis patient.

Creatinine. In anuric patients, a change in creatinine can indicate a change in muscle mass. A downward trend in creatinine may indicate a decrease in muscle mass, which can have far- reaching consequences. Loss of muscle mass can result in weakness, falls, and an inability to do activities of daily living, eventually compromising quality of life and possibly leading to the onset of depression.

Blood urea nitrogen (BUN). Protein that is taken into the body produces BUN. A declining BUN can be indicative of decreasing food intake, potentially leading to a decline in albumin levels and muscle mass. This will affect the protein catabolic rate as well, as it is determined from the pre- and post-BUN.

Lipid profile. Elevated lipid levels are very difficult to treat with diet alone. Adding additional parameters to the diet will further reduce food options in an already limited diet, risking further compromise of nutritional status. Attempts to reduce saturated fat intake and simple sugars will he made when possible, however, lipid-lowering medications may be necessary to achieve goals. Low serum cholesterol without the use or initiation of a lipid-lowering medication should be viewed as a marker of insufficient food intake rather than a positive change in lipid status.

Other Labs

Sodium. Serum sodium levels are not a direct indication of sodium intake, but rather hydration status. Patients assume that normal serum sodium levels mean they aren't eating too much salt. Patients often notice that the more salt they eat, the lower their serum sodium level becomes, thus assuming that their sodium intake is desirable, when in fact they are further compounding the issue of fluid overload.

Bicarbonate. Predialysis serum levels should be maintained at or above 22 mmol/L. It is vital to maintain acid--base balance, as acidosis predisposes the patient to muscle protein degradation and hyperkalemia (National Kidney Foundation, 2000).

Vitamins. Since water-soluble vitamins are lost during the dialysis procedure, serum levels are monitored to ensure compliance with the prescribed vitamin and avoid symptoms of vitamin deficiency.

Urea reduction ratio. Adequacy of treatment is critical to ensure avoidance of uremic symptoms such as nausea and vomiting, which will cause further compromise in food intake.

A Recipe for Good Health

Initially, patients look to their RD for recipes to help them cope with their complex diet, but ultimately, the RD provides a recipe for good health by closely monitoring all lab values and the patient's body composition to piece together the entire picture to maintain optimal health.

References

McCann, L. (Ed.). (2002). Pocket guide to nutrition assessment of the patient with chronic kidney disease (3rd Edition), pp. 2-1-2-22.

National Kidney Foundation. (2000). NKF-K/DOQI clinical practice guidelines for nutrition in chronic renal failure. American Journal of Kidney Diseases, 35, S38-S39.

Janelle Gonyea, RD, LD, is Clinical Dietitian, Mayo Clinic Dialysis Services, Rochester, MN.
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Title Annotation:Focus on Nutritional Care for Nephrology Patients
Author:Gonyea, Janelle
Publication:Nephrology Nursing Journal
Date:Dec 1, 2003
Words:1068
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