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Sample

Precautions

Purpose of the test

  1. Creatinine level is done to assess kidney function.
  2. creatinine can be advised to see any effect of blood pressure or diabetes on the kidney.
  3. Creatinine is advised to monitor the renal diseases.
  4. Creatinine may be measured in amniotic fluid to assess the gestational (fetal) age and (fetal-maturity index), and cephalosporins.

Pathophysiology

  1. Creatinine is the end product of catabolism of creatine phosphate.
    1. Free creatinine is a waste product of creatine metabolism, is present in all body fluids and secretions.
    2. It is freely filtered by the glomerulus.
    3. There is diurnal variation when it is low at 7 AM and high at 7 PM.
    4. There is a slight increase after the meal and especially after the meat in the diet because a small amount is present in the meat.
    5. There is a very little effect by the liver function.
  2. Creatine phosphate is used in the contraction of skeletal muscles, by providing the energy.
    1. Creatinine is the waste product formed in the muscles from high energy compound creatine phosphate.

  1. The daily production of creatine and creatinine is dependent upon the muscle mass.
    1. The daily excreted creatinine is the function of muscle mass and is not dependent upon:
      1. Age.
      2. Sex.
      3. Diet.
      4. Exercise.
      5. Women excrete less creatinine than men because of less muscle mass.
      6. The daily excretion of the creatinine is relatively constant and is ±15% for a person per day.
        1. Creatinine excretion is not affected by protein metabolism or other external factors.
        2. So serum creatinine is the best measure of glomerular function (filtration).
        3. Creatinine is raised only when the 50% function of the kidney is lost.
        4. There is a minimal amount of creatinine in the urine from tubular secretion.
        5. Creatinine amount in the urine increases as the creatinine concentration rises in the blood.

  1. Creatinine is entirely excreted by the kidneys so directly proportional to the kidney function.
    1. Creatinine level remains normal with the normal excretory function of kidneys.
      1. Creatinine is excreted by the glomeruli as the filtrate and then it is not absorbed by the tubules.
      2. If there is any problem with glomerular filtration function then its level will increase in the blood.

    1. So renal disorders of kidneys give rise to increase in creatinine level like:
      1. Glomerulonephritis.
      2. Acute tubular necrosis.
      3. Pyelonephritis.
      4. Urinary obstruction.
  1. This is more specific and sensitive parameter of the renal function and renal disease than blood urea nitrogen.
  2. This is specific for renal function and gives an idea about renal dysfunction.
  3. This is not a sensitive indicator of early renal disease.
  4. For 50% reduction in GFR, serum creatinine level will be double.
  5. BUN/creatinine ratio is important to evaluate the renal function.
    1. Normal in adult = 6 to 25 
    2. Optimum level = 15.5

Normal

Source 1

Age mg/dL    
Cord blood 0.6 to 1.2    
Newborn 1 to 4 day 0.3 to 1.0    
Infants 0.2 to 0.4    
Child 0.3 to 0.7    
Adolescent 0.5 to 1.0 Male Female
18 to 60 year   0.9 to 1.3 0.6 to 1.1
>90 year   1.0 to 1.7 0.6 to 1.3

 

Source 5

Serum creatinine and creatinine clearance with the condition of the patient:

Serum creatinine mg/dL Creatinine clearance mL/minute  The condition of the patient
0.6 to 1.3 100 ± 20  normal person
1.4 to 2.4 61 to 99 still Seen in active person
2.5 to 4.9 24 to 60 difficulty in performing the physical activity
5.0 to 7.9  12 to 23 the patient cannot do daily activity
8 to 12 7 to 12 acidosis and severe limitation of the activity
>12 6 or less patient in a coma and disorientated

Increased creatinine may be due to three causes:

  1. Pre-renal.
  2. Renal.
  3. Post-renal.
  4. Pre-renal factors are:
    1. Congestive heart failure.
    2. Shock.
    3. Salt and water depletion due to:
      1. Vomiting.
      2. Diarrhea.
      3. GIT fistulas.
      4. Increased use of diuretics.
      5. Uncontrolled diabetes mellitus.
      6. Diabetes insipidus.
      7. Excessive sweating (decreased salt intake).
  5. Renal factors are:
    1. Damage to:
      1. Glomerulus.
      2. Tubules.
      3. Interstitial tissue.
      4. Blood vessels.
  6. Post-renal factors are:
    1. Benign prostatic hyperplasia.
    2. Neoplasia compressing the ureter.
    3. Calculi obstructing the ureter.
    4. Congenital abnormalities obstructing or compressing the ureter.

The increased level is seen in:

  1. Renal function impairment both acute and chronic diseases.
  2. Postrenal obstruction of urine.
  3. Decrease in the blood perfusion because of any reason.
  4. Gigantism and Acromegaly.
  5. Injury to the muscles (Rhabdomyolysis).
  6. Myasthenia gravis.
  7. Poliomyelitis.
  8. Muscular dystrophy.
  9. Dehydration due to loss of body fluids.
  10. May be seen in pregnancy during eclampsia and preeclampsia.

The decreased level is seen in:

  1. Old-age.
  2. Decreased muscle mass.
  3. Pregnancy especially in a first and second trimester.
  4. Advanced and severe liver disease.
  5. inadequate dietary intake.

Drugs leading to an increased level of creatinine:

  1. Gentamicin.
  2. cimetidine.
  3. Heavy metals chemotherapy e.g. Cisplatin.
  4. Nephrotoxic drugs like Cephalosporin e.g. Cefoxitin.
Interfering factors:
  1. Ascorbic acid can increase creatinine level.
  2. A diet high in protein like meat can increase the level.

The critical value is >4 mg/dL suggest severe renal disease.

 


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