Labs to Assess in Renal Disease

<< Back

Labs to Assess in Renal Disease

Posted on 18th Oct 2017

Note: Normal range for lab values may vary depending on reference used or a laboratory’s reference values.

Blood urea nitrogen (BUN)

  • BUN is a nitrogenous waste product of protein metabolism
  • It is elevated with:
    • Increased protein intake
    • Catabolism
    • Gastrointestinal (GI) bleeding
    • Decreased dialysis efficiency
  • It is lowered with:
    • Low protein intake
    • Loss of protein because of emesis or diarrhea
    • Frequent dialysis
    • Protein anabolism
    • Overhydration
  • Normal value is 7–23 milligrams (mg)/deciliter (dL); accepted value for dialysis patients is 50–100 mg/dL

Creatinine (Cr)

  • Cr is a nitrogenous waste end product of muscle metabolism
  • It is not directly affected by diet like BUN and minimally affected by fluid intake
  • The amount produced each day is proportional to the body’s muscle mass; useful for assessing muscle mass changes in renal patients and changes in renal function
  • A Cr level double the normal level suggests a 50% nephron loss, whereas a serum Cr of 10 mg/dL suggests a 90% nephron loss or end-stage renal disease
  • The following changes in dialysis can cause sudden elevations in serum Cr:
    • Skipped dialysis treatments
    • Shorter dialysis time
    • Poor blood flow through an access
  • Normal value is 0.6–1.4 mg/dL; for dialysis patients, desired value varies with physician

Lipids

  • In renal diseases, elevated lipid levels often are correlated with cardiovascular disease
  • Dialysis patients often have type IV hyperlipoproteinemia patterns with elevated triglycerides
  • Elevated triglycerides and cholesterol levels often are seen because lipoprotein lipase activity is decreased in renal failure and clearance of triglycerides is reduced
  • Diet can control hyperlipoproteinemia in renal patients to some extent, but this is difficult because the renal diet already involves numerous restrictions
  • The diet to control hyperlipoproteinemia involves reduced simple carbohydrates and increased polyunsaturated/saturated fats (P/S) ratio
  • Normal range for triglycerides is less than 150 mg/dL

Sodium (Na)

  • Na is the principle cation of extracellular fluid
  • Functions include:
    • Preservation of normal muscle
    • Irritability and contractibility
    • Maintenance of acid-base equilibrium
    • Osmotic pressure of body fluids
    • Permeability of cells
  • Serum Na is not used to assess Na intake in renal disease, because fluid retention can dilute an elevated Na level, making it appear normal
  • Hypernatremia causes include:
    • Excess water loss
    • Diarrhea
    • Vomiting
    • Excess diuretics
  • Hypernatremia symptoms may possibly include:
    • Flushed skin
    • Dry tongue
    • Thirst
  • Hyponatremia causes include:
    • Fluid overload
    • Na depletion
  • Hyponatremia symptoms may possibly include:
    • Abdominal cramps
    • Hypotension
  • Normal value is 135–145 milliequivalents (mEq)/dL; a normal value is desired for dialysis patients

Potassium (K)

  • K is the principle cation of the intracellular fluid
  • Hyperkalemia can result in:
    • Cardiac arrhythmias
    • Muscle weakness
    • Death
  • Causes of hyperkalemia include:
    • Excessive intake of dietary K
    • Fever
    • Infection
    • Surgery
    • GI bleeding
    • Catabolism
    • Acidosis
  • Causes of hypokalemia include:
    • Reduced dietary intake of K
    • Vomiting
    • Diarrhea
    • Excessive use of K binders
    • Dialysis against a low K bath
  • Normal value is 3.5–5.5 mEq/L; a normal value is desired for dialysis patients

CO2 (bicarbonate)

  • An elevated CO2 combining power indicates alkalosis and intracellular acidosis in absence of chronic obstructive pulmonary disease (COPD)—most frequently correlated with hypokalemia and a decreased C1 level
  • A decreased CO2 combining power occurs with metabolic acidosis, such as:
    • Uremic acidosis
    • Diabetic ketoacidosis
    • Lactic acidosis
    • Renal tubular acidosis
  • However, if blood pH is elevated (alkalosis), a decreased combining power indicates respiratory alkalosis, as seen in hyperventilation syndrome
  • The normal value is 24–32 mEq/L

Chloride (Cl)

  • Cl influences acid-base balance
  • An elevated level is associated with:
    • Renal tubular acidosis
    • Decreased CO2 combining power
    • Hypokalemia
    • Certain drugs, including carbonic anhydrase inhibitors (used to treat glaucoma)
    • Dehydration
    • Metabolic acidosis
    • Respiratory alkalosis
  • A decreased Cl is associated with hypokalemia and alkalosis
  • An elevated Cl and low CO2 is diagnostic of renal tubular acidosis, which is often secondary to chronic renal failure
  • A normal value is 96–106 mEq/L

Hemoglobin/hematocrit (Hb/Hct)

  • A low Hb/Hct often is an indication of anemia, but you need to assess mean corpuscular volume (MCV), mean corpuscular hemoglobin concentration (MCHC), mean corpuscular hemoglobin (MCH), red blood cells (RBC), and ferritin to determine anemia type
  • An elevated BUN level alters the Fe (iron) level with uremic patients, so you need to assess the ferritin level
  • Fe deficiency causes include:
    • GI bleeding
    • Frequent blood sampling
    • Loss from dialyzer
    • Decreased Fe absorption
    • Inadequate Fe intake
    • Increased RBC production in dialysis patients
  • Hypochromic microcytic anemia is indicated by decreased Hb/Hct, MCV (microcytic), MCHC (hypochromic), and serum Fe; most common cause is Fe deficiency from diet, but another cause is upper GI bleeding
  • Normochromic normocytic anemia is indicated by decreased Hb/Hct and normal MCV and MCH; seen with loss of RBC mass, as in hemorrhage or hemolysis
  • The normal results for hematocrit vary, but in general are as follows:
    • Male: 40.7%–50.3%
    • Female: 36.1%–44.3%
    • Dialysis patients: Acceptable levels are toward the lower end of the range, depending on the physician
  • The normal range for hemoglobin is generally:
    • Male: 13.8–17.2 grams (g)/dL
    • Female: 12.1–15.1 g/dL
    • Dialysis patients: Acceptable levels are toward the lower end of the range, depending on the physician

Ferritin

  • The storage form of Fe
  • A low ferritin level often is seen in chronic renal patients
  • In renal disease, anemia is caused by decreased production in RBCs, secondary to:
    • Reduced erythropoietin
    • Hemolysis of RBCs
    • Increased blood loss through the GI tract and periodic blood sampling
  • In renal disease, other losses occur from dialyzer blood loss, membrane rupture, and prolonged bleeding from access site
  • Causes of an elevated ferritin level include:
    • Frequent blood transfusion
    • Oversupplementation of Fe
    • Infection
  • Normal value is:
    • Male: 20–35 micrograms (mcg)/liter (L)
    • Female: 6–350 mcg/L
    • Dialysis patients: Acceptable values are 300–800 mcg/L, depending on the physician

Serum protein

  • Total protein, serum albumin, and transferrin are not ideal indicators of nutritional status, because they can become altered in renal disease
  • Uremia appears to affect albumin metabolism, which can affect its concentration
  • Transferrin has a shorter half-life (8–9 days), as compared to albumin (19–20 days), which indicates it is possibly a more sensitive indicator; however, transferrin is affected by Fe deficiency, which elevates transferrin or Fe loading, which decreases the serum level  
  • Albumin and transferrin levels run lower in renal patients compared to healthy subjects, and also lower in poorly nourished renal patients compared to well-nourished renal patients:
    • Levels are not as sensitive to changes in nutritional status
    • Levels do not always correlate with other nutritional parameters
    • Albumin levels are dependent on hydration status and the value is affected by hemoconcentration
  • Normal value of albumin is 3.4–5.4 g/dL; a normal value is desired for dialysis patients, with a preference for values greater than 4.0 g/dL

Calcium (Ca)

  • 99% of the Ca is found in bones and teeth
  • In renal disease, decreased Ca absorption exists, secondary to the abnormal metabolism of vitamin D
  • Hyperphosphatemia also leads to decreased serum Ca levels, which then contribute to secondary hyperparathyroidism and renal osteodystrophy
  • Symptoms of hypocalcemia include:
    • Tingling fingers
    • Abdominal cramps
    • Convulsions
    • Tetany
    • Cardiac or respiratory arrest
  • To maintain normal Ca levels, you may give Ca and vitamin D supplements or increase the calcium concentration in the dialysis bath
  • Normal value is 8.5–10.8 mg/dL; 8.5–10.5 mg/dL is desired for dialysis patients

Phosphorus (PO4)

  • 80% of the PO4 is combined with Ca in hard tissues of the body
  • In renal disease, increased PO4 contributes to decreased Ca and secondary hyperparathyroidism  
  • To lower PO4 level, restrict phosphorus in the diet and/or use phosphorus binders
  • Normal value is 2.5–4.5 mg/dL; 3.5–5.5 mg/dL is desired for dialysis patients

Ca-PO4 product

  • To obtain the Ca-PO4 product, multiply the serum Ca by the PO4 level
  • The goal is to keep this level at less than 55 to prevent metastatic calcification, which is the development of Ca deposits in any soft tissue areas, such as the heart, blood vessels, lungs, conjunctivae of the eye, and the extremities

 

References and recommended readings 
Academy of Nutrition and Dietetics. Nutrition Care Manual® . Available to subscribers at: www.nutritioncaremanual.org. Accessed January 8, 2013.

DaVita®. Understanding your lab work. Available at: http://www.davita.com/kidney-disease/overview/symptoms-and-diagnosis/understanding-your-lab-work/e/4724. Accessed January 8, 2013.

Mahan LK, Escott Stump S, Raymond JL. Krause’s Food and the Nutrition Care Process. 13th ed. St Louis, MO: Elsevier Saunders; 2012. 

 


Contact Us Today


By Phone:

1-888-856-0137

By Email:

info@foodfitnessfirst.com

Mailing Address:

P.O. Box 980 Vidalia, GA 30475


"The FOOD SPIRAL®" is a registered trademark of Food Fitness First, Inc.

All other trademarks and service marks are the properties of their respective owners.

©2017 Food Fitness First, Inc®
Phone: 1-888-856-0137