CREATININE

Creatinine is a break-down product of creatine phosphate in muscle, and is usually produced at a fairly constant rate by the body (depending on muscle mass).

PHYSIOLOGY:

Creatinine is mainly filtered by the kidney, though a small amount is actively secreted. There is little-to-no tubular reabsorption of creatinine.

If the filteration of the kidney is deficient, blood levels rise. As a result, creatinine levels in blood and urine may be used to calculate the creatinine clearance(ClCr), which reflects the glomerular filtration rate (GFR).

The GFR is clinically important because it is a measurement of renal function. However, in cases of severe renal dysfunction, the creatinine clearance rate will be "overestimated" because the active secretion of creatinine will account for a larger fraction of the total creatinine cleared.

Ketoacids, cimetidine and trimethoprim reduce creatinine tubular secretion and therefore increase the accuracy of the GFR estimate, particularly in severe renal dysfunction. (In the absence of secretion, creatinine behaves like inulin.)

A more complete estimation of renal function can be made when interpreting the blood (plasma) concentration of creatinine along with that of urea.

Urea concentration is given as blood urea nitrogen, in mg/dL. BUN-to-creatinine ratio; ratio of urea to creatinine can indicate other problems besides those intrinsic to the kidney for example, a urea level raised out of proportion to the creatinine may indicate a pre-renal problem such as dehydration.

Men tend to have higher levels of creatinine because they have more skeletal muscle than women.

Vegetarians tend to have lower creatinine levels, because vegetables contain no creatinine

DIAGNOSTIC USE:

Measuring serum creatinine is a simple test and it is the most commonly used indicator of renal function.

A rise in blood creatinine levels is observed only with marked damage to functioning nephrons. Therefore, this test is not suitable for detecting early stage kidney disease.

A better estimation of kidney function is given by the creatinine clearance test.

CREATININE TESTS

Three types of tests on creatinine can be done:

1. BLOOD CREATININE LEVEL:

o The blood creatinine level shows how well kidneys are working.

o A high creatinine level may mean kidneys are not working properly. The amount of

creatinine in the blood depends partly on the amount of muscle tissue; men generally

have higher creatinine levels than women.

2. CREATININE CLEARANCE TEST:

A creatinine clearance test measures how well creatinine is removed from blood by kidneys.

o A creatinine clearance test gives better information than a blood creatinine test on how

well kidneys are working.

o A creatinine clearance test is done on both a blood sample and on a sample of urine

collected over 24 hours (24-hour urine sample).

3. BLOOD UREA NITROGEN-TO-CREATININE RATIO

o The levels of blood creatinine and blood urea nitrogen (BUN) can be used to find the

BUN-to-creatinine ratio.

o A BUN-to-creatinine ratio can help for problems, such as dehydration, that may cause

abnormal BUN and creatinine levels.

Creatinine clearance is calculated from the formula:

Urine Creatinine concentration x Urine volume (ml)

CrCl (ml/min) = ___________________________________________________

Serum Creatinine concentration x Period of collection (min)

SIGNIFICANCE OF CREATININE CLEARANCE TEST

A blood creatinine level or a creatinine clearance test is done to:

See if kidneys are working normally.

See if kidney disease is changing.

See how well the kidneys work in people who take medicines that can cause kidney

damage.

See if severe dehydration is present. Dehydration generally causes BUN levels to rise

more than creatinine levels. This causes a high BUN-to-creatinine ratio. Kidney disease or

blockage of the flow of urine from your kidney causes both BUN and creatinine levels to rise.

HOW TO PREPARE:

o Do not do any strenuous exercise for 2 days (48 hours) before having creatinine tests.

o Do not eat more than 8 oz (227 g) of meat, especially beef, or other protein for 24 hours

before the blood creatinine test and during the creatinine clearance urine test.

o It is important to drink enough fluids during the 24-hour urine collection but do not

drink coffee and tea. These are diuretics that cause your body to pass more urine.

o Stop taking drugs that may affect the test. Such drugs include:

Aminoglycosides (for example, gentamicin) Bactrim Cimetidine Heavy metal chemotherapy drugs (for example, Cisplatin) Nephrotoxic drugs such as cephalosporins (for example, cefoxitin) Vitamin C Methyldopa Trimethoprim Phenytoin

RESULTS

o Creatinine and creatinine clearance tests measure creatinine levels in blood and urine to

give information about how well kidneys are working.

o The creatinine clearance value is found from the amounts of creatinine in the urine and

blood and from the amount of urine passed in 24 hours.

o This value is the amount of blood cleared of creatinine per minute, based on body size.

REFERANCE RANGEBlood Creatinine: Men 0.6–1.2 (mg/dL) or 53-106 (mcmol/L)

Women 0.5–1.1 mg/dL or 44–97(mcmol/L)

Teen 0.5–1.0 mg/dL

Child 0.3–0.7 mg/dL

Newborn 0.3–1.2mg/dLConversion Fromula:Serum: µmol/L x 0.011 = mg/dlUrine: µmol/24 hours = mg/24 hours

Creatinine Clearance: Men 90–140 milliliters per minute (mL/min) or 1.78–2.32 milliliters per

second (mL/sec)

Women 80–125 mL/min or 1.45-1.78 mL/sec

Creatinine clearance values normally go up as you get older (normal values go down by 6.5

mL/min for every 10 years past the age of 20).

BUN to Creatinine Ratio:

Over 12 months of age: 10:1 - 20:1

Infants(less than 12 months of age): Upto 30:1

o While a baseline serum creatinine of 2.0 mg/dL (150 μmol/l) may indicate normal kidney function in a male body builder, a serum creatinine of 0.7 mg/dL (60 μmol/l) can indicate significant renal disease in a frail old woman.

o More important than absolute creatinine level is the trend of serum creatinine levels over time.

o Creatinine levels may increase when ACE inhibitors (ACEI) or angiotensin-II receptor blockers (ARBs) are used in the treatment of chronic heart failure (CHF).

HIGH VALUES

HIGH CREATININE BLOOD LEVELS:

High creatinine blood levels can mean serious kidney damage or disease is present. Kidney damage

can be caused by a life-threatening infection, shock, cancer, or low blood flow to the kidneys.

Other conditions that can cause high blood creatinine levels include

Blockage of the urinary tract (such as by a kidney stone),

Heart Failure,

Dehydration, excessive blood loss that causes shock,

Gout,

Muscle conditions (such as rhabdomyolysis, gigantism, acromegaly, myasthenia gravis,

muscular dystrophy, and polymyositis).

Usually a high blood creatinine level means that the creatinine clearance value is lower than

normal.

HIGH CREATININE CLEARANCE:

High creatinine clearance values can be caused by strenuous exercise,

Muscle injury (especially crushing injuries),

Burns

Carbon monoxide poisoning,

Hypothyroidism, and

Pregnancy.

HIGH BUN-TO-CREATININE RATIO:

o High BUN-to-creatinine ratios occur with sudden (acute) kidney failure, which may be

caused by shock or severe dehydration.

o A blockage in the urinary tract (such as a kidney stone) can cause a high BUN-to-

creatinine ratio.

o A very high BUN-to-creatinine ratio may be caused by bleeding in the digestive tract or

respiratory tract.

LOW VALUES

LOW BLOOD CREATININE LEVELS:

o Low blood creatinine levels can mean lower muscle mass caused by a disease, such as

muscular dystrophy, or by aging.

o Low levels can also mean some types of severe liver disease or a diet very low in protein.

o Pregnancy can also cause low blood creatinine levels.

LOW CREATININE CLEARANCE:

o Low creatinine clearance levels can mean serious kidney damage is present.

o Kidney damage can be from conditions such as a life-threatening infection, shock, cancer,

low blood flow to the kidneys, or urinary tract blockage.

o heart failure,

o dehydration,

o liver disease (cirrhosis),

LOW BUN-TO-CREATININE RATIO

o A low BUN-to-creatinine ratio may be associated with a diet low in protein,

o a severe muscle injury called rhabdomyolysis,

o pregnancy,

o cirrhosis,

o Syndrome of inappropriate antidiuretic hormone secretion (SIADH).

o SIADH sometimes occurs with lung disease, cancer, diseases of the central nervous

system, and the use of certain medications.

SERUM CREATININE ESTIMATION

PRINCIPLE:

Kinetic Calorimetric assay: Alkaline Creatinine + Picric acid Creatinine - Picric acid complex Solution

In alkaline solution, creatinine forms a yellow-orange complex with picrate. The color intensity is directly proportional to the creatinine concentration and can be measured photo metrically.

REAGENTS:

R1:

Picric acid

R2:

Sodium hydroxideDilute 1 volume of R1 with 1 volume of R2 . Label it as Working Solution. It is stable for 10 days at + 2 0C – 8 0C or 1 day at + 20 0C – 25 0C

STANDARD: Creatinine SPECIMEN:

Collect serum using standard sampling tubes.

TESTING PROCEDURES:

ASSAY CONDITIONS:

Wavelength: 492nm(480-520nm) Temperature: +370C Cuvette: 1cm light path Zero adjustment: air or distilled water

B S UStandard - 100 µl -Sample - - 100 µlReagent Distilled Water 1.0 ml 1.0 ml

Mix, pour immediately into the cuvettes. After exactly 20 seconds, take readings of sample and standard (T1 and S1 respectively).Exactly 80 seconds after the first reading, take another reading of sample and standard (T2 and S2 respectively).

CALCULATIONS:

T1 = ____________________

T2 =____________________

S1 =____________________

S2 = ____________________

∆T = T2 - T1 =___________________

∆S = S2 - S1 =____________________

Conc. of Standard = 2mg/dl

Creatinine (mg/dl) = ∆T ------ x Conc. Of Standard ∆S

=

Creatinine (mg/dl) = ______________