Clinical Chemistry Final

Non-protein nitrogen compounds used to monitor renal function:
Urea.
Creatinine.
Uric Acid.

*Ammonia – monitors liver function.

How urea is made in the liver:
Ammonia + CO2
Blood urea concentration depends on these:
Renal function.
Protein content of diet.
Protein breakdown.
Azotemia:
Increased blood urea.
Uremia:
Excessive blood urea accompanied by renal failure.
Pre-renal azotemia may be due to:
Congestive heart failure.
Renal azotemia may be due to:
Glomerulonephritis.
Post-renal may be due to:
Blockage due to a stone or a tumor.
Most common is pancreatic.
Decreased Serum Urea may be due to:
SIADH.
Malnutrition.
Pregnancy.
Person has decreased urea. Also has water retention. Diagnosis?
Water retention is causing urea to be diluted – not necessarily true decreased urea.
How to determine urea measurement: (Formula)
Bun (mg/dL) x 2.14 = mg urea/dL

(remember 2.14)

Uric acid – should it be used as an indicator for kidney function?
No – it is not the best indicator of kidney function because 98% is reabsorbed.
Uric acid is the product of:
Purine metabolism: adenosine and guanine.
Where is uric acid reabsorbed?
98% is reabsorbed in the proximal tubule.
The rest is excreted by the GI.
Where is uric acid secreted?
The distal tubule – about 70%.
When is uric acid insoluble?
At the pH of plasma (monosodium urate).
– at concentrations > 6.4 mg/dL = ppt.
Insolubility of uric acid causes what disease?
Gout – insolubility causes crystals (precipitate) to form which causes gout.
Major diseases associated with increased plasma uric acid:
– Gout.
– Renal disease.
– Increased breakdown of nucleic acid – cell turnover (Leukemia)
– Toxemia of Pregnancy (preeclampsia and eclampsia – electrolytes all out of whack)
What is gout?
Uric acid ppt (crystals) in the blood.
– Swelling, stiffness, pain in the interstitial joint spaces.
Risk factors of gout:
Alcohol.
Exposure to lead in the environment.
High purine diet.
Medications that interfere with the body’s ability to remove uric acid.
Medications for gout:
Cyclosporine.
Methotrexate.
Allopurinol.
Probenicid.
Where is Creatinine synthesized?
In the liver.
What is creatinine synthesized from?
Arginine.
Glycine.
Methionine.
What is creatinine primarily used as?
An anaerobic muscle source by muscle.
Why is creatinine a good marker for glomerular filtration?
Because it is filtered by the kidney at a constant rate.

(Creatinine would need to be measured in blood and urine to determine kidney function)

Jaffee Reaction:
creatinine + alkaline picrate —> red/orange chromagen
BUN:Creatinine ratio
10:1 – often described as a ratio to serum creatinine.

This helps differentiate between pre-renal and renal conditions…

Pre-renal conditions elevate plasma urea, but not creatinine — high ratio.

Low BUN/Creatinine ratio is seen with decreased protein intake, liver disease.

Normal Creatinine Clearance ranges:
Normal Male: 85-125 mL/min/1.73 m2

Normal Female:75-115 mL/min/1.73 m2

Creatinine Shortcut Formula:
(140 – age)(weight kg) / 7.2 x serum creatinine (mg/L)
Low Creatinine Clearance levels mean:
Renal Impairment: 50-100 ml/min/1.73m2

Renal Insufficiency: 10-50 ml/min/1.73m2

Uremia: <10 ml/min/1.73m2

How does creatinine clearance affect serum creatinine?
As creatinine clearance goes down, serum creatinine goes up.
Abnormally high creatinine levels mean:
(increased GFR)
High protein diet.
Intense exercise.
Incomplete urine collection.
Pregnancy.
Abnormally low creatinine levels mean:
Acute tubular necrosis.
Dehydration.
Congestive heart failure.
Glomerulonephritis.
Shock.
Renal ischemia (blood deficiency)
Acute renal failure.
Chronic renal failure.
Acute nephritic syndrome.
End-stage renal disease.
Wilms’ Tumor
Rapidly progressive glomerulonephritis.
Acute bilateral obstructive uropathy.
What makes ammonia?
Deaminating proteins.
Major source of circulating ammonia comes from where?
GI tract.
How much ammonia is normally found in the blood?
Only trace amounts.
When should you give a child aspirin?
NEVER. Causes toxicity to the liver, can cause brain damage and death. (ammonia builds up)
Are amino acids routinely measured in serum and urine?
No.
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