Renal Function Test: BUA, BUN and Creatinine

RENAL FUNCTION TEST (RFT)

            The major function of the kidneys is to eliminate waste products from the body and reabsorbed the substances essential for body function. When the kidneys’ functions are impaired, one or both processes are altered. 

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Measurements of the ability of the kidneys to carry out their major processes provide vital data in knowing whether they’re normally functioning or not.

           

            To know whether a kidney functions correctly we may perform different tests such as, test for Blood Urea Nitrogen (BUN), Creatinine and Blood Uric Acid (BUA).

CREATININE

            Creatinine is used to diagnose impaired renal function.

            This test measures the amount of creatinine in the blood. Creatinine is a catabolic product of creatinine phosphate, which is used in skeletal muscle contraction. 

The daily production of creatine and subsequently creatinine depends on muscle mass, which fluctuates very little. 

Creatinine, as BUN, is excreted entirely by kidneys and therefore is directly proportional to renal excretory function. Thus, with normal renal excretory function, the serum creatinine level should remain constant and normal. 

Only renal disorders such as glomerulonephritis, pyelonephritis, acute tubular necrosis, and urinary obstruction, will cause an abnormal elevation in creatinine. 

There are slight increases in creatinine levels after meals, especially after ingestion of large quantities of meat. Furthermore, there may be some diurnal variation in cr.

           

            The serum creatinine test, as with the BUN, is used to diagnose impaired renal function. Unlike BUN, however, the creatinine level is affected minimally by hepatic function. 

The serum creatinine level has much the same significance as the BUN level but tends to rise later. Therefore elevations in creatinine suggest chronicity of the disease process. 

In general, a doubling of creatinine suggests a 50% reduction in the glomerular filtration rate. The creatinine level is interpreted in conjunction with the BUN.

             

NORMAL VALUES:

v  ELDERLY         decrease in muscle mass may cause decreased values

v  ADULT

FEMALE        0.5-1.1 mg/dL or 44-97 umol/L

MALE             0.6-1.2 mg/dL or 53-106 umol/L

v  ADOLECENT                        0.5-1.0 mg/dL

v  CHILD                       0.3-0.7 mg/dL

v  INFANT                     0.2-0.2 mg/dL

v  NEWBORN               0.3-1.2 mg/dL

INTERFERING FACTORS

v  A high diet in meat content can cause transient elevations of serum creatinine.

v  Drugs may increase creatinine values include aminoglycoside (e.g. gentamicin), cimetidine, heavy-metal chemotherapeutic agents (e.g. cisplatin), and other nephrotoxic drugs such as cephalosporins (e.g. cefoxitin)

TEST RESULTS AND CLINICAL SIGNIFICANCE

    LEVELS

Disease affecting renal function, such as glomerulonephritis, pyelonephritis, acute     tubular necrosis, urinary tract obstruction, renal blood flow (e.g. shock, dehydration, congestive heart failure, atherosclerosis), diabetic nephropathy, nephritis. With these illnesses, renal function is impaired and creatinine levels rise.

Rhabdomyolysis. Injury of the skeletal muscle causes myoglobin to be released in the blood stream. Large amounts are nephrotoxic. Creatinine levels rise.

Acromegaly

Gigantisim

These diseases are associated with increased muscle mass, which causes the “normal” creatinine level to be high

    LEVELS

Debilitation

Decreased muscle mass (e.g. muscular dystrophy, myasthenia gravis)

The diseases are associated with decreased muscle mass, which causes “normal” creatinine level to be low.