Renal Function and Nonprotein Nitrogen
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What is increased in plasma indicating renal impairment?
All non-protein nitrogens (urea, creatinine, uric acid, and ammonia).
Define azotemia.
The increase of non-protein nitrogens in plasma.
What is the best laboratory evaluation when suspecting renal impairment?
Glomerular Filtration Rate (GFR).
What is used to evaluate the GFR?
Creatinine clearance; more sensitive than BUN or creatinine.
What is the calculation used for creatinine clearance?
((U creat)/(P creat)) x ((Volume 24-hr urine)/(1440 (min/24hr)))
What test takes the patient’s demographics into consideration for its calculation?
eGFR.
Creatinine is synthesized from…
creatine in the muscle.
(T/F) Creatinine is used to evaluate renal function and is NOT as sensitive as GFR.
True.
What method is used for creatinine testing? Describe this method.
Jaffe reaction; creatinine reacts with picric acid in basic solution, forms a red-orange complex, and read at 490-540 nm.
What are some analyte interferences to creatinine testing?
Glucose, acetoacetate, and ascorbic acid.
Blood urea nitrogen (BUN) is increased in what condition? How does high-protein diets affect BUN?
Impaired renal function; increases with high protein diets.
What are the two testing methods used for BUN measurement?
Colorimetric and enzymatic methods.
What enzyme is used in the enzymatic method of BUN measurement?
Urease.
Normal BUN/Creatinine ratio.
10:1 - 20:1.
Cystatin C is a serum marker for ___.
GFR.
What method is used to measure cystatin C?
Immunoassay.
Describe A1 Albuminuria.
24-hr urine albumin: <30 mg/24hr (N to mild ↑).
Describe A2 Albuminuria.
24-hr urine albumin: 30-300 mg/24hr (moderate ↑).
Describe A3 Albuminuria.
24-hr urine albumin: >300 mg/24hr (Severely ↑).
Uric acid is the end product of ___ metabolism.
purine.
Uric acid is increased in what conditions?
Gout, renal failure, leukemia, and chemotherapy treatments.
What testing method is used for uric acid? What analyte interferences may cause altered results?
Colorimetric method; lipids and drugs.
What is a by-product of the enzymatic assay of uric acid?
Hydrogen peroxide.
Ammonia is synthesized from…
the action of bacteria on the contents of the colon; metabolized by liver normally.