NON-PROTEIN NITROGEN COMPOUNDS

what are the major NPN compounds, in order of abundance?

• urea

• creatinine

• uric acid

• ammonia

what is azotemia?

increased nitrogenous waste products in blood

what is uremia?

severe accumulation of waste products accompanied by clinical symptoms

the urea cycle occurs primarily in ________

hepatocytes

the urea cycle converts ________ into urea

toxic ammonia

what does BUN measure?

the concentration of urea-derived nitrogen in blood

what does urease do?

hydrolyzes urea, producing ammonia ions

plasma containing what substances should be avoided in the urease-GLDH method?

• ammonium salts

• sodium citrate

• sodium fluoride

what does the urease-GLDH method measure?

NADH consumption at 340 nm

common symptoms of uremia

• fatigue

• nausea

• vomiting

• confusion

what causes prerenal azotemia?

decreased renal blood flow

what causes renal azotemia?

intrinsic kidney damage

what causes postrenal azotemia?

obstruction of urine flow

what is the normal BUN/creatinine ratio?

10:1 to 20:1

how does prerenal azotemia affect the BUN/creatinine ratio?

BUN rises disproportionately, with the ratio often increasing

how does renal azotemia affect the BUN/creatinine ratio?

BUN and creatinine rise together, with the ratio often remaining normal

what conditions may cause decreased BUN?

• severe liver disease

• low protein intake

• pregnancy

what is uric acid?

the end product of purine metabolism

approximately what fraction of uric acid is eliminated through the kidneys?

two-thirds

what is hyperuricemia?

increased uric acid concentration in blood

what causes gout?

deposition of monosodium urate crystals in tissues

what are causes of hyperuricemia due to increased production?

• leukemia

• chemotherapy

• tumor lysis syndrome

• high cellular turnover

what are causes of hyperuricemia due to decreased excretion?

• renal disease

• impaired renal function

what does creatinine function as?

a rapid energy reserve for muscle contraction

what is creatinine converted to within muscle cells to help regenerate ATP?

phosphocreatine

what is creatinine?

a normal byproduct of muscle metabolism, produced from creatine and phosphocreatine

what occurs in the Jaffe reaction?

creatinine reacts with alkaline picrate and produces a colored complex

what substances may affect the Jaffe reaction?

• glucose

• ketones

• proteins

• certain medications

what might elevated creatinine indicate?

• acute kidney injury

• chronic kidney disease

• decreased eGFR

what is ammonia?

highly toxic amino acid metabolism waste product

what are causes of hyperammonemia?

• liver disease

• urea cycle disorders

• severe metabolic disorders

what causes hepatic encephalopathy?

accumulation of neurotoxic substances due to impaired liver detoxification

what are symptoms of hepatic encephalopathy?

• confusion

• altered mental status

• personality changes

• decreased level of consciousness

most ammonia testing methods utilize which enzyme?

glutamate dehydrogenase (GLDH)

how should specimens for ammonia testing be handled?

placed on ice immediately and transported rapidly