Creatinine Blood Test|Definition and Patient Education

Creatinine Blood Test

Definition and Patient Education

Kidney Function Panel

Definition and Patient Education

I) Introduction

This topic is for general information about creatinine test but it includes sections for medical technicians and medical lab specialist and links referring to these sections. If you want to read the technical sections, follow the links that refer to it.

1) Names:-

Formal name: Creatinine

Also known as: Creat; Blood Creatinine; Serum Creatinine.

2) What is the Creatinine?

Creatinine is a nitrogenous waste product resulted from creatine breakdown in the skeletal muscle through a chemical cycle for producing energy needed for muscle contraction. Creatinine is water-soluble and hence it can diffuse freely to the water of the extracellular fluid of the blood. Almost all of creatinine excreted mainly by kidneys and it is also relatively constant in normal conditions. So, the creatinine concentration in blood is a good indicator for how healthy your kidneys are.

Creatinine level in blood is higher in men than in women and children because it depends on the person size and muscle mass.

3) Why it is required?

To detect and investigate kidney dysfunction and to monitor kidney disease.

4) When should you get tested?

  • As part of the health checkup.
  • When someone feels ill without specific health complaints.
  • When the physician thinks that you have symptoms of a kidney dysfunction such as:-
    • Fatigue, lack of concentration, loss of appetite, difficulty in sleeping.
    • Swelling, particularly around the eyes or in the face, wrists, abdomen, thighs, or ankles.
    • Urine that is foamy, bloody, or coffee-colored.
    • Low amount of urine.
    • Burning feeling or abnormal discharge during urination, or a change in the frequency of urination, especially at night.
    • Mid-back pain (flank i.e. discomfort in your upper abdomen or back), below the ribs, near where the kidneys are located
    • High blood pressure
  • When your doctor wants to follow up the condition of kidney disorder.
  • When you suffer from a disease that may affect the kidney function such as HIV disease, you should follow up the kidney function.
  • When you take drugs such as nephrotoxic antiretroviral drugs used for HIV treatment, you should check your kidney function before and during taking these drugs

5) What are the needed preparations before the test?

The patient should be instructed to fast or refrain from eating cooked meat before the test because cooked meat increases the creatinine level.

Stop taking the following drugs before the test:-

  • Aminoglycosides (for example, gentamicin)
  • The antifungal medicine amphotericin B, cimetidine (Tagamet), phenytoin (Dilantin), quinine, quinidine, procainamide,methyldopa, trimethoprim (Proloprim, Trimpex), or vitamin C (ascorbic acid).
  • Heavy metal chemotherapy drugs (for example, Cisplatin)
  • Kidney damaging antibiotics such as cephalosporins antibiotics especially cefoxitin (Mefoxin), tetracycline antibiotics, and
  • Diuretics

II) Required sample:-

This section is for medical technicians or medical lab specialists. If you want to read it, read in Required sample for creatinine blood test in lab.


III) The Test:-

This is section for medical technicians or medical lab specialists. If you want to read it, read in Procedure of creatinine blood test in lab


IV) Sources of errors:-

This is section for medical technicians or medical lab specialists. If you want to read it, read in Sources of errors in creatinine blood test in lab


V) Quality Control:-

This is section for medical technicians or medical lab specialists. If you want to read it, read in Quality control of creatinine blood test in lab.


VI) Interpretation of test results:-

Creatinine is a nitrogenus waste product of creatine breakdown in muscles to produce the energy required for muscle contraction. Therefore, the larger muscle mass, the more energy needed, the higher rate of creatine breakdown, the higher creatinine level is. This means that Creatinine level is related to the muscle mass. In addition, cooked or roast meat contains creatinine and hence eating cooked meat increases creatinine level. Creatinine is excreted by kidney and hence, if the kidney is damaged, creatinine will accumulate in blood and its level will be higher than normal.

So, creatinine test is used to:-

  • Diagnose renal insufficiency (i.e. kidney diseases).
  • Adjusting dosage of renal excreted medications.
  • Monitoring renal transplant recipients.
  • Diagnose reduced skeletal muscle mass (muscle dysfunction).


Increased In

  • Eating cooked or roast meat.
  • In the case of muscle mass increment as in gigantism, acromegaly.
  • Pre- and postrenal azotemia.
  • Impaired kidney function but 50% loss of renal function is needed to increase serum creatinine from 1.0 to 2.0 mg/dL. Therefore, the test is not sensitive for mild to moderate renal injury.
  • Some drugs can increase serum Creatinine such as aminoglycosides and penicillins (especially methicillin).

Decreased In

  • Pregnancy: Normal value is 0.4–0.6 mg/dL. A value >0.8 mg/dL is abnormal and should alert the clinician to further diagnostic evaluation.
  • Treatment by certain drugs (e.g., cimetidine, trimethoprim).
  • Reduced skeletal muscle mass (i.e. Muscle dystrophy).

Limitations

  • Artifactual decrease by:
    • Marked increase of serum bilirubin
    • Glucose >100 mg/dL.
  • Artifactual increase due to
    • Reaction of picrate with other substance such as glucose, ascorbate, uric acid.
    • Ketoacidosis may substantially increase serum creatinine results with alkaline picrate reaction.
    • Formation of colored complexes (e.g., acetoacetate, pyruvate, other ketoacids, certain cephalosporins).
    • Other methodologic interference (e.g., ascorbic acid, phenolsulfonphthalein, l-dopa).
    • Some medications inhibit tubular secretion of creatinine, thereby decreasing creatinine clearance and increasing serum creatinine without a change in GFR. These medications include the following:
      • Cephalosporin and aminoglycoside antibiotics
      • Flucytosine
      • Cisplatin
      • Cimetidine
      • Trimethoprim

References:-

  • labtestonline.org
  • Wallach’s Interpretation of Diagnostic Tests Pathways to Arriving at a Clinical Diagnosis

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