Serum Creatinine

What Sample is needed for serum creatinine?

1. This test is done on serum(clotted blood 3-5 ml) or plasma.
2. The plasma may be prepared in fluoride or heparin.
   • Fluoride or heparin is not suitable for the enzymatic methods of creatinine.
3. The sample is stable for 24 hours when kept at 4 °C.
4. The non-fasting sample is acceptable.

What precautions for serum creatinine are essential?

1. No preparation is needed, and a random sample can be taken.
2. Lipemic and hemolyzed samples give a falsely high level.
3. Heparin and fluoride are not suitable for the enzymatic procedure.
4. Excessive exercise and a high-meat diet increase the level.
5. Drugs may increase the level, such as gentamicin, cimetidine, and chemotherapy (cisplatin),

What are the Indications for estimating serum creatinine?

1. Creatinine level is used to assess kidney function.
2. Creatinine can be used to assess the effect of blood pressure or diabetes on the kidneys.
3. Creatinine is recommended for monitoring renal diseases.
4. Creatinine may be measured in amniotic fluid to assess the gestational (fetal) age and fetal-maturity index, and cephalosporins.

How will you define creatinine?

1. Creatinine is the end product of creatine metabolism.
2. Creatinine is a product of the breakdown of creatine, a nitrogen-containing compound largely found in the muscles.
3. Creatinine is a waste product formed in the muscles.
4. Creatinine in the muscles is formed by the high-energy storage compound creatine phosphate, also called phosphocreatine.
   1. The above reaction is not reversible, and the creatinine is excreted in the urine.

How will you discuss the pathophysiology of creatinine?

1. Creatinine is produced by muscle metabolism. It depends upon the body’s muscle mass; the greater the muscle mass, the higher the creatinine in serum and urine.
2. Creatinine is the end product of the catabolism of creatine phosphate.
   1. Free creatinine, a waste product of creatine metabolism, is present in all body fluids and secretions.
   2. The glomerulus freely filters it.
   3. There is a diurnal variation, with low levels at 7 AM and high levels at 7 PM.
   4. There is a slight increase after the meal, and especially after the meat in the diet (20% to 25%) because a small amount is present in the meat.
   5. There is very little effect on liver function.
3. Creatine phosphate is used in the contraction of skeletal muscles by providing energy.
   1. Creatinine is the waste product formed in the muscles from the high-energy compound creatine phosphate.

4. The daily production of creatine and creatinine is dependent upon muscle mass.
5. A small amount of creatinine is ingested as a meat component, but this does not affect the serum creatinine level. There is a raised level of creatinine only seen in the case of kidney disease.
6. Creatinine in the blood has a stable concentration, and variation is <10% in 24 hours.

What is the mechanism of Creatinine excretion?

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

What is the role of the kidneys in creatinine metabolism?

1. Creatinine level remains normal with the normal excretory function of the kidneys.
2. The glomeruli excrete creatinine as the filtrate (15% to 20% of the plasma creatinine), which is not absorbed by the tubules.
3. If there is any problem with glomerular filtration function, the level of waste products will increase in the blood.
4. Creatinine is a by-product of skeletal muscle creatine phosphate metabolism.
5. Creatinine is filtered across the glomerular filtration barrier and enters the Bowman space. It is not reabsorbed, secreted, or metabolized by the tubular cells. So, creatinine excreted in the urine per minute equals the amount of creatinine filtered in the Bowman space.

6. So renal disorders of the kidneys give rise to an increase in creatinine levels, such as:
   1. Glomerulonephritis.
   2. Acute tubular necrosis.
   3. Pyelonephritis.
   4. Urinary obstruction.
7. Creatinine is a more specific and sensitive parameter of renal function and renal disease than blood urea nitrogen.
   1. This is specific to renal function and provides insight into renal dysfunction.
   2. This is not a sensitive indicator of early renal disease.
   3. For a 50% reduction in GFR, the serum creatinine level will double.

• The serum creatinine concentration is a better indicator of renal function than uric acid and BUN.

What is the role of the kidneys in excretion, reabsorption, and filtration?

How will you define the BUN/creatinine ratio?

• It is important to evaluate renal function.

1. Normally, the BUN/creatinine ratio is 10:1.
2. Under standard conditions, a 50% decrease in the GFR will roughly double the BUN or creatinine level.
3. 1. Normal in adults = 6 to 25
   2. Optimum level = 15.5

What are the Normal values of serum creatinine?

Source 1

• To convert to SI unit x 88.4 = µmol/L

Source 5

• Child = 0.3 to 0.7 mg/dl
• Adult = 0.5 to 1.0 mg/dl
• 18-60 years :
  • male = 0.9 to 1.3 mg/d
  • Female = 0.6 to 1.2 mg/dl
• Above 90 years
  • Male =1.0 to 1.7 mg/dl
  • Female = 0.6 to 1.3 mg/dl

Source 6

1. Adult
   1. Malle = 0.6 to 1.0 mg/dL  (53 to 106 µmol/L)
   2. Female = 0.5 to 1.1 mg/dL  (44 to 97 µmol/L)
   3. Elderly = Decrease in muscle mass, causing a decreased value
2. Adolescent = 0.5 to 1.0 mg/dL
3. Child = 0.3 to 0.7 mg/dL
4. Infants = 0.2 to 0.4 mg/dL
5. Newborn = 0.3 to 1.2 mg/dL

What is normal Urinary creatinine?

1. Male = 14 to 26 mg/Kg/day  (124 to 230 µmol/Kg/day).
2. Female = 11 to 20 mg/Kg/day  (97 to 177 µmol/Kg/day).
   1. Creatinine excretion in the urine decreases with age.

What will be the Serum creatinine and creatinine clearance with the condition of the patient?

What are the causes of increased serum creatinine?

1. Pre-renal.
2. Renal.
3. Post-renal.

What are the pre-renal causes of increased serum creatinine?

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).

What are the causes of raised renal serum creatinine?

1. Damage to:
   1. Glomerulus.
   2. Tubules.
   3. Interstitial tissue.
   4. Blood vessels.

What are the causes of raised Post-renal serum creatinine?

1. Benign prostatic hyperplasia.
2. Neoplasia compresses the ureter.
3. Calculi obstructing the ureter.
4. Congenital abnormalities obstruct or compress the ureter.

What are the causes of increased serum creatinine?

1. Renal function impairment is both an acute and chronic disease.
2. Postrenal obstruction of urine.
3. Decrease in blood perfusion for 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. It may be seen in pregnancy during eclampsia and preeclampsia.

What are the causes of decreased serum creatinine?

1. Old-age.
2. Decreased muscle mass.
3. Pregnancy, especially in the first and second trimesters.
4. Advanced and severe liver disease.
5. Inadequate dietary intake.

What are the drugs leading to an increased level of serum creatinine?

1. Gentamicin.
2. Cimetidine.
3. Heavy metals chemotherapy, e.g., Cisplatin.
4. Nephrotoxic drugs like Cephalosporin, e.g., Cefoxitin.

What are the factors that interfere with serum creatinine estimation?

1. Ascorbic acid can increase creatinine levels.
2. A diet high in protein, like meat, can increase the level of serum creatinine.

• The critical value is >4 mg/dL, suggesting severe renal disease.

Questions and answers: