7/28/2019 Creatinine Lab Card

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creatinine, blood (Serum creatinine) Type of test: Blood

Adult Female: 0.5-1.1 mg/dL or 44-97 mol/L (SI units)

Adult Male: 0.6-1.2 mg/dL or 53-106 mol/L (SI units)

Elderly: decrease in muscle mass may cause decreased valuesPossible critical values: >4 mg/dL (indicates serious impairment in renal function)

Drugs that may increase creatinine values include ACE inhibitors, aminoglycosides (e.g., gentamicin),

cimetidine, heavy-metal chemotherapeutic agents (e.g., cisplatin), and other nephrotoxic drugs, such as

cephalosporins (e.g., cefoxitin).

Increased levels: Glomerulonephritis, Pyelonephritis, Acute tubular necrosis, Urinary tract obstruction,

Reduced renal blood flow (e.g., shock, dehydration, congestive heart failure, atherosclerosis), Diabeticnephropathy, Nephritis, Rhabdomyolysis, Acromegaly, Gigantism

Decreased levels: Debilitation, Decreased muscle mass (e.g., muscular dystro- phy, myasthenia gravis)

Procedure and patient care Before: Explain the procedure to the patient. Tell the patient that no fasting is required.

During: Collect a venous blood sample in a red-top tube. For pediatric patients, blood is usually

drawn from a heel stick.

After: Apply pressure to the venipuncture site.

creatinine, blood (Serum creatinine) Type of test: Blood

This test measures the amount of creatinine in the blood. Creatinine is a catabolic product of creatine phosphate, which

is used in skeletal muscle contraction. The daily production of creatine, and subsequently creatinine, depends on musclemass, which fluctuates very little. Creatinine, as with blood urea nitrogen (BUN, see p.944), is excreted entirely by the

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. Besides dehydration, only such renal disorders asglomerulonephritis, pyelonephritis, acute tubular necrosis, and urinary obstruction will cause abnormal elevations in

creatinine. There are slight increases in creatinine levels after meals, especially after ingestion of large quantities ofmeat. Furthermore, there may be some diurnal variation in creatininenadir at 7 am and peak at 7 pm.

The serum creatinine test, as with BUN, is used to diagnose impaired renal function. Unlike BUN, however, the

creatinine level is affected very little by hepatic function. The creatinine test is used as an approximation ofglomerular

filtration rate (GFR). 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 suggestsa 50% reduction in GFR. The creatinine level is interpreted in conjunction with the BUN test. These tests are referred to

as renal function studies. The BUN/creatinine ratio is a good measurement of kidney and liver function. The normal

adult range is 6 to 25, with 15.5 being the optimal adult value for this ratio

Although serum creatinine is the most commonly used biochemical parameter to estimate GFR in routine practice, there

are some shortcomings. Such factors as muscle mass and protein intake can influence serum creatinine, leading to an

inaccurate estimation of GFR. Moreover, in unstable, critically ill patients, acute changes in renal function can makereal-time evaluation of GFR using serum creatinine difficult. On the other hand, cystatin C, a protein that is produced at

a constant rate by all nucleated cells, is probably a better indicator of GFR. Because of its constant rate of production, its

serum concentration is determined only by glomerular filtration. Its level is not influenced by those factors that affect

creatinine and BUN.

Cystatin C might predict the risk for developing chronic kidney disease, thereby signaling a state of preclinical kidney

dysfunction. Several studies have found that increased levels of cystatin C are associated with the risk of death and

several types of cardiovascular disease (including MI, stroke, heart failure, peripheral arterial disease, and metabolic

syndrome). For women, the average reference interval is 0.52 to 0.90 mg/L with a mean of 0.71mg/L. For men, the

average reference interval is 0.56 to 0.98 mg/L with a mean of 0.77 mg/L.

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