U2.3 NPN : Uric Acid [L] Flashcards by EJ E

Q

One of the non-protein nitrogenous compounds

A

Blood Uric Acid

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Q

Byproduct of purine nucleic acid catabolism

A

Blood Uric Acid

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Q

where is BUA produced

A

liver

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Q

where is BUA filtered

A

glomerulus

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Q

% of BUA is reabsorbed in the proximal tubules

A

98-100%

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Q

Main form of BUA in Plasma

A

monosodium urate

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Q

T/F Clinical application of BUA include to confirm diagnosis and monitor treatment of gout

A

T

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Q

T/F Clinical application of BUA include prevent uric acid nephropathy during chemotherapeutic treatment

A

T

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Q

T/F Clinical application of BUA include assess inherited disorders of pyrimidine metabolism

A

F; purine

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Q

T/F Clinical application of BUA include to detect liver dysfunction

A

F; kidney

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Q

T/F Clinical application of BUA include assist in the diagnosis of renal calculi

A

T

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Q

BUA Determination

Uric Acid > Allantoin uses what enzyme

A

Uricase

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Q

BUA Determination : Chemical Method

based on reduction of phosphotungstic acid in alkaline solution to tungsten blue

A

Caraway Method

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Q

BUA Determination : Chemical Method

non-specific and requires protein removal

A

Caraway Method

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Q

BUA Determination : Chemical Method

In a carbonate solution (Na2CO3/OH-):
uric acid + H3PW12O40 + O2 →

A

allantoin + tungsten blue + CO2

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Q

BUA Determination

Uses uricase enzyme to catalyze oxidation of uric acid to allantoin

A

Enzymatic Methods

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Q

BUA Determination

More specific and more commonly used

A

Enzymatic Methods

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Q

BUA Determination : Enzymatic Methods

measures the hydrogen peroxide produced as uric acid is converted to allantoin

A

Coupled enzymatic reaction

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Q

BUA Determination : Enzymatic Methods

color produced is directly proportional to uric acid concentration

A

Coupled enzymatic reaction

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Q

BUA Determination : Enzymatic Methods

Coupled enzymatic reaction sources of error

A

reducing agents (bilirubin and ascorbic acid)

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Q

BUA Determination : Enzymatic Methods

In coupled enzymatic reactions, hydrogen peroxide produced as uric acid is converted to _____

A

allantoin

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Q

BUA Determination : Enzymatic Methods

measures differential absorbance before and after incubation with uricase at 293 nm

A

Spectrophotometric assay

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Q

BUA Determination : Enzymatic Methods

Spectrophotometric assay sources of error

A

presence of protein, hemoglobin and xanthine

Q

BUA Determination : Enzymatic Methods

difference is directly proportional to uric acid concentration

A

Spectrophotometric assay

BUA Determination : Other Methods typically uses UV detection

High-performance liquid chromatography (HPLC)

BUA Determination : Other Methods proposed candidate reference method

Isotope Dilution Mass Spectrometry (IDMS)

BUA Determination : Other Methods detects characteristic fragments following ionization

Isotope Dilution Mass Spectrometry (IDMS)

BUA Determination : Other Methods quantifies uric acid using isotopically labeled compound

Isotope Dilution Mass Spectrometry (IDMS)

Specimen Considerations in BUA Determination Specimens

heparinized plasma, serum or urine

T/F In BUA Determination, fasting is not required

T

Hemolytic samples Falsely Increase/Decrease

Falsely decrease

Icteric samples Falsely Increase/Decrease

Falsely decrease

Lipemic Samples Falsely Increase/Decrease

Falsely increase; background interference

Additives that should not be used for BUA determination

EDTA and Fluoride additives

Assay requirements Wavelength Optical path Temperature

Wavelength: 546 nm Optical path: 1 cm Temperature: 37 ͦ C

Assay Requirements should be read against _____

reagent blank

Concentration of Standard Urine

88 mg/dL

Concentration of Standard Serum or plasma

6 mg/dL

Reference Range Plasma or Serum Male Adult

3.5-7.2

Reference Range Plasma or Serum Female Adult

2.6-6.0 mg/dL

Reference Range Plasma or Serum Child

2.0-5.5 mg/dL

Reference Range Urine (24h)

250-750 mg/day

Clinical Significance caused by gout, lactic acidosis, chronic renal disease, drugs & poisons

Hyperuricemia

Clinical Signifance caused by liver disease, defective tubular reabsorption, chemotherapy & overtreatment w allopurinol

Hypouricemia

Clinical Significance Defective tubular reabsorption

Fanconi syndrome

Sources of Error (falsely increase or falsely decrease) Bilirubin

falsely increase / false positive

Sources of Error (falsely increase or falsely decrease) Vitamin C

falsely increase / falsely positive

Sources of Error (falsely increase or falsely decrease) Presence of protein

falsely increase

Sources of Error (falsely increase or falsely decrease) Hemoglobin

falsely decrease

Sources of Error (falsely increase or falsely decrease) Xanthine

falsely decrease

Color of quinoneimine dye

red-violet

enzyme that hastens oxidation of uric axid to allantoin

Uricase

In the presence of uricase, uric acid is converted to ___ and _____

allantoin and hydrogen peroxide

The formed hydrogen peroxide reacts under the catalysis of what enzyme?

Peroxidase

Hydrogen peroxide + 4-AAP + EHSPT >

quinoneimine + HCl + 4H2