CLINICAL CHEMISTRY (MLT 301) NONPROTEIN NITROGEN (NPN) LECTURE TWO

1
CLINICAL CHEMISTRY (MLT 301)NONPROTEIN
NITROGEN(NPN)LECTURE TWO

• Dr. Essam H. Jiffri

2
URIC ACID

• Uric acid is the final breakdown product of
  purine metabolism.
• Most mammals have the ability to catabolize
  purines one step further to allantoin, a much
  more water-soluble end-product.
• - Purines such as adenosine and guanine,
  resulting from the breakdown of nucleic acids
  that are ingested or come from the destruction of
  tissue cells, are converted into uric acid,
  mainly in the liver.

3
URIC ACID

• Uric acid is transported by the plasma from the
  liver to the kidney, where it is filtered by the
  glomerulus.
• - The uric acid in the glomerular filtrate, 98
  to 100 is reabsorbed in the proximal tubule,
  small amounts of uric acid are then secreted by
  the distal tubules and ultimately appear in the
  urine.

4
URIC ACID

• The most important disease associated with
  elevated levels of uric acid in the plasma is
  gout.
• Gout is a disease found primarily in males and
  usually first diagnosed between the ages of 3O
  and 50.
• - Patients have pain and inflammation of the
  joints caused by precipitation of sodium urates
  in the joint resulting from the high levels of
  uric acid found in extracellular fluids

5
Analytical Methods

• - Uric acid is readily oxidized to allantoin and
  thus can function as a reducing agent in many
  reactions.

6
(No Transcript)
7
Analytical Methods

• - The most poplular method of this type is the
  Caraway method, which is based on the oxidation
  of the uric acid in a protein-free filtrate, with
  subsequent reduction of phosphotungstic acid to
  tungsten blue.

8
(No Transcript)
9
Specimen Requirementsand Interfering Substances

• Uric acid may be determined in serum, urine, or
  heparinized plasma.
• Significant hemolysis, which releases
  glutathione, also may give low values a number
  of drugs, such as thiazides and salicylates, have
  been shown to cause elevated values for uric acid.

10
Specimen Requirementsand Interfering Substances

• Diet in general may affect the uric acid levels,
  the patient need to be fasting.

11
Intervals Reference

• Values are slightly lower in children and
  premenopausal females.
• Children 2.0-5.5 mg/dl (0.12-0.32 mmol/L)
• Adult males 3.5-7.2 mg/dl (0.12-0.42 mmo/L)
• Adult female 2.6-6.0 mg/dl (0.15-0.35
  mmol/L)

12
AMMONIA

• - The level of ammonia in the circulation is
  extremely low (11-35 µmol/L).
• - It arises from the deamination of amino acids,
  which occurs mainly through the action of
  digestive and bacterial enzymes on proteins in
  the intestinal tract.

13
AMMONIA

• Ammonia is also released from metabolic reactions
  that occur in skeletal muscle during exercise.
• - Severe liver disease represents the most
  common cause of disturbed ammonia metabolism.

14
Analytical Methods

• There are two distinct approaches that have been
  used for the measurement of plasma ammonia.
• One is a two-step approach in which ammonia is
  first isolated from the sample and then assayed.
• - The second involves direct measurement of
  ammonia by an enzymatic method or ion-selective
  electrode.

15
(No Transcript)
16
Specimen Requirements and Interfering Substances

• Ammonia levels rise rapidly in whole blood after
  drawing because of the deamination of amino
  acids.
• - EDTA is the preferred anticoagulant.

17
Specimen Requirements and Interfering Substances

• - Samples should be centrifuged at 0 to 40C
  within 20 minutes of collection, and the plasma
  removed, and frozen plasma is reportedly stable
  for several days at -200C.
• - Because red cells contain 2 to 3 times as much
  ammonia as plasma, hemolysis should be avoided.

18
Reference Intervals

• Ammonia 14 to 49 µg/dL (11-35 µmol/L)