Unit 4

Objectives: By the completion of this unit the learner will

1. Describe functions of kidneys
2. Describe renal regulation of body water and electrolytes.
3. Identify common imbalances in the internal environment related to renal dysfunction.
4. Discuss nursing management of imbalances in the electrolytes, fluid and acid-base related to renal dysfunction.

Required Reading:  Corbett, J.V. (2008). Laboratory tests and diagnostic procedures with nursing diagnoses. 7th Ed. pp. 90-107.

Recommended Readings:

·        Understanding Renal Function Tests http://www.rnceus.com/renal/renalframe.html

·        Understanding Urinalysis http://www.rnceus.com/ua/uaframe.html

·        Clinical Evaluation of GU Disorders http://www.merck.com/mrkshared/mmanual/section17/chapter214/214a.jsp

·        Acid-Base Balance http://www.merck.com/mrkshared/mmanual/section2/chapter12/12b.jsp

Areas Covered:

            Specific Gravity

            Blood Urea Nitrogen (BUN)

            Creatinine Levels in Serum

            BUN to Creatinine Ratio

            Serum and Urine Osmolality

            Uric Acid (Serum and Urine)

Urine Specific Gravity -  crude indicator of fluid statusA measure of the DENSITY of urine compared with the density of water

Normal Values: Adult 1.001-1.040  Infants and children < 2 years 1.001-1.018

Increased Specific Gravity

• Dehydration
• Increased ADH- SIADH: Trauma, surgery, stress, drugs
• False high= glucose, protein, or dye in urine

Decreased Specific Gravity

• Renal failure - fixed sp grav
• Glomerulonephritis, pyelonephritis
• Decreased ADH (diabetes insipidus)

Blood Urea Nitrogen (BUN)

Normal  value: 8-25 mg/dL (adult)

Metabolism:

Major nitrogenous end product of protein and amino acid catabolism

 Produced by liver and distributed throughout intracellular and extracellular fluid

In kidneys almost all urea is filtered out of blood by glomerular function. Some urea reabsorbed with water but most is removed in urine

Decreased BUN

• Fluid excess - especially a concern with IV fluids
• SIADH - trauma, surgery, opioids,
• Liver failure - urea synthesized by liver
• Malnutrition
• Anabolic Steroid use
• Pregnancy - dilutional

Increased BUN

• Dehydration
• High protein diet
• GI bleed  
• Impaired renal function
• CHF - poor renal perfusion
• Shock
• MI
• Excess protein catabolism

Serum Creatinine - Definitive test of renal function

Normal values

• Children
• Men 
• Women

Creatinine Metabolism

• Nonketone wase product of creatine phosphate metabolism by skeletal muscle tissue.  Proportional to muscle mass.
• High levels of ascorbic acid or barbiturates can distort results.
• Ketones and cephalosporin antibiotics may elevate
• The elderly and young children normally have lowercreatinine. This can potentially mask renal disease in these patients.

Obtaining the Sample 

• Red-topped tube – 10 ml venous blood; Infants & small children heelstick to fill capillary pipette
• Excessive turbulance can caue false measurements
• Prolonged delay in sending to lab can cause ammonia to form
• Warming can cause falsely elevated results
• Creatinine rises and falls more slowly than BUN. Preferred method for assessment of renal function.

Decreased Creatinine

• Elderly
• Persons with small stature, decreased muscle mass
• Inadequate dietary protein
• Muscle atrophy
•  

Increased Creatinine Levels  - Loss of more than 50% of nephrons

Nephrotoxic Medications: Creatinine level used to monitor the administration of nephrotoxic medications

Creatinine Clearance Test

Normal = Male: 1-2 g/day, female: 0.8-1.8 g/day

The total amount of creatinine excreted in urine in a 24 hour period is called creatinine clearance

During renal failure, diminished glomerular filtration occurs thus increasing the secretion of creatinine in the serum.

In chronic renal failure and uremia becomes very severe, an eventual reduction occurs in the excretion of creatinine by both the glomeruli and the tubules.

Creatinine is excreted entirely by the kidneys and therefore directly proportional to the GFR.  So clinically it can be seen as a measure of GFR.  With unilateral kidney disease or nephrectomy, a decreased creatinine clearance is NOT expected if the other kidney is normal.

** Incomplete collections will falsely decrease creatinine clearance.

• Decreases by 10% per decade after age 40 years whereas serum creatinine shows little variation 
• **Used to assess renal function and creatinine excretion. Used to monitor the progression of renal disease
• Elevated values with muscular dystrophy paralysis, anemia, leukemia hyperthyroidism
• Decreased values with glomerulonephritis, CHF, acute tubular necrosis, shock , polycystic kidney disease, dehydration
• Can be shortened to 2, 4, 8 or 12 hours but best is 24 hrs. Needs to be refrigerated or on ice.
• Instruct patient to avoid excessive intake of meat before the test, encourage adequate hydration before and urine test and omit coffee and tea
• Usually instruct patient to void at 8:00 am then all subsequent urine specimens are collected for 24 hrs.
• No vigorous exercise,
• Label container with proper time and date

Serum Osmolality

** Used to assess the patient’s FLUID status and Identify any ADH abnormalities.

Osmolality is a measure of the number of particles dissolved in a solution.

Osmolality is affected by increases or decreases in fluid volume or by an increase or decrease in blood particles

In blood osmolality is created by protein, glucose, chloride, sodium, bicarbonate and urea dissolved in the plasma.

Normal Values:    Adults: 285-298 mOsm/kg

Increased values = alcoholism, aldosteronism, diabetes insipidus, high protein diet, dehydration, hypercalcemia, hyperglycemia, hypernatremia & hyperkalem ia

Decreased values = fluid overload, hyponatremia, liver failure with ascites, Addison's disease   

4 interfering factors

1.      Medications

2.      Diuretics

3.      Hemolysis of specimen

4.      Mineralocorticoids

Urine Osmolality

Normal Average: 500-800 mOsm/kg H₂O 

Collected from a 24-hour urine specimen or 2-5 ml sample

Osmolality varies based on the patient’s fluid status and metabolic waste products being excreted

Purpose = Assess the ability of kidneys to dilute or concentrate urine and identify ADH abnormalities

Increased values = “Kidneys are conserving water” -- dehydration, Addison's disease, diabetes mellitus, diarrhea, hyperglycemia, hypernatremia cirrhosis

Decreased values = overhydration, hyponatremia, hypocalcemia, aldosteronism, diabetes insipidus

Serum Uric Acid

Normal value: Male  3.6-8.5 mg/dL, female = 2.3 – 6.6 mg/dL

Uric acid is end product of protein metabolism and excreted by kidneys and bowels

Temporary increase in serum uric acid from ingestion of food high in purine (meat, fish), strenuous exercise,or heavy alcohol ingestion

• will usually return to normal within 1 day

Purpose of test is to confirm the diagnosis of gout and helps detect renal impairment that causes prerenal azotemia and renal failure

Patient sample: Overnight fasting

Interfering factors: starvation, caffeine, vitamin C ingestion, high purine diet

Increased Serum Uric Acid 

• Gout
• Renal Failure
• Medications– thiazides
• Preeclampsia
• Cell destruction– neoplasms
• Prolonged fasting/malnourishment–  (cell breakdown)

Treatment: Lots of fluids 

Key Points

1. Creatinine is marker of renal function, not BUN
2. BUN:creatinine ratio is one method to differentiate prerenal from intrarenal failure.
3. Increased creatinine level means loss of nephron function, intrarenal failure
4. BUN is affected by hydration, GI bleed, protein intake
5. Major component of serum osmolality is sodium in normal conditions