Sunday, July 26, 2015

Renal Function Test: BUA, BUN and Creatinine


            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 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.


v  ELDERLY         decrease in muscle mass may cause decreased values
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


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)



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.

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


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.

Saturday, July 18, 2015

Potassium, the Major Intracellular Cation

Potassium is the primary intracellular cation. It is also an integral part of the transmission of nerve impulses.  It participates in the sodium-potassium pump in the body. 

Unhemolyzed serum should be used because hemolysis will markedly increase the potassium values because potassium is present in large amounts inside the cell.

Clinical Significance

1.      Hyperkalemia – increased concentration of potassium in the bloodstream. It’s found in the following conditions:

         Decreased renal excretion

         Acute or chronic renal failure
         Addison’s disease

·         Cellular shift

         Muscle/cellular injury

Increased intake

             Oral or IV potassium replacement therapy

-          Artifactual

                        Sample hemolysis
                        Prolonged tourniquet use of excessive fist clenching

2.      Hypokalemia – decreased concentration of potassium in the blood stream, seen in the following conditions:

            GI loss

                        - Vomiting
                        - Diarrhea
                        - Gastric suction
                        - Intestinal tumor
                        - Malabsorption
                        - Cancer therapy
                        - Large doses of laxatives

          Normal values:

                           K = 3.5-5.3

         Plasma and serum: 3.4 – 5.0 mmol/L
         Urine: 25 -125 mmol/L