Non-Protein Nitrogens

NPN constituents

urea, creatine/creatinine, uric acid, ammonia

how are NPNs formed

from the breakdown of proteins and nucleic acids

which NPN makes up the largest fraction

urea

where are NPNs synthesized

liver

urea plasma measurements

BUN

BUN

blood urea nitrogen

azotemia

elevated urea in the blood

uremia

very high levels of urea accompanied with renal failure

prerenal azotemia

caused by reduced renal blood flow (less urea to kidneys, less urea filtered out)

decreased renal function

causes an increase in plasma urea concentration due to compromised urea excretion

postrenal azotemia

caused by an obstruction to the urine flow anywhere in the urinary tract

reference range for BUN/Creatinine ratio

10:1 to 20:1

BUN analytical methods

use urease to convert urea into ammonium ions and quantitate:

enzymatic method

indicator dye and reagent strips

conductimetric method

normal range for BUN

7-18 mg/dL

creatinine source

creatine is synthesized in the liver, then broken down to form creatinine

three sources related to plasma creatinine levels

relative muscle mass, rate of creatine turnover, and renal function

creatinine clearance

measures renal function (glomerular filtration)

clearance of a substance

the volume of plasma from which that substance is cleared per unit time

CrCl formula

CrCl = U(Cr) x V(U) / P(Cr) x t mL/min

are CrCl results corrected for muscle mass

yes, because they are related to muscle mass

most common CrCl analytical method

Jaffe reaction: creatinine reacts with picric acid

male and female ranges for creatinine

male: 0.9-1.3 

female: 0.6-1.1

uric acid source

from the breakdown of nucleic acids or tissue destruction

elevated uric acid level diseases

gout, increased nucleic acid catabolism, renal disease

hyperuricemia

increased level of uric acid in the plasma

uric acid analytical methods

uricase (enzymatic method) or coupled enzymatic method

normal ranges for uric acid

male: 3.5-7.2

female: 2.6-6.0

ammonia source

from the breakdown of amino acids

elevated ammonia conditions

hepatic failure and Reye’s syndrome

ammonia special handling

must be placed on ice immediately to prevent amino acid breakdown

normal ammonia ranges

19-60 microgram/dL