Terms in this set (84)

- Determined by renal regulation of blood HCO3- reabsorption and H+ excretion levels
- No "correct" pH - any pH can be normal
- Limited role as guide to body acid-base balance except ruminants.
- pH 5 to pH 8.5 is measured on a dipstick pad if the strip is only dipped into the urine for ≈1 second and the excess urine tapped off immediately .'. not always accurate
- Instrumentally read strips will tend to underestimate below 6.5 and overestimate over 7.5 relative to visually reading; i.e. a wider range of results will be seen.
- Most dogs and cats have urine pH 5.5 - 7.0 as they excrete predominantly acid salts of phosphates
- Adult herbivores produce alkaline urine (pH 7.0 - 9.0) due to obligatory excretion of alkaline salts of carbonates.
- Normal suckling foals have acidic urine pH <7.0.
- Alkaline urine is associated with
i. Urinary tract infections with urease-producing bacteria
ii. Metabolic and respiratory alkalosis
iii. Recent meal (carnivores)
iv. Diets rich in vegetables
v. Distal renal tubule acidosis.
- Struvite and calcium phosphate crystals tend to form in alkaline urine.
- Horses produce acidic urine with prolonged periods of anorexia and with metabolic acidosis.
- Ruminants suffering of ketosis or chronic rumen acidosis often produce acidic urine
Practical Hints
- Contamination with urease-splitting bacteria (eg from the perineum) will increase pH.
- Some types of bacterial contamination decrease pH.
- Storage at room temperature will increase pH (CO2 escapes).
- Detergents and disinfectants will increase pH (important if sucked up off the table or floor).
- A small amount of protein may be present in the urine of all species
- Urine containing a large amount of protein will "froth" if shaken.
- Positive results for protein imply glomerular leakage or inflammation in the genitourinary tract
- Proteinuria must also be interpreted in light of the SG
i. Dilute urine = a large amount of protein must be excreted before being detectable .'. animals with isosthenuria, hyposthenuria & trace protein reactions may be losing lots of protein. Overcome by the use of the urine protein:creatinine ratio
- Physiologic/functional proteinuria = transient & associated with exercise
- Glomerular proteinuria = leakage of plasma protein through damaged glomeruli at a rate which exceeds the tubular capacity to reabsorb protein. Initially, there is the loss of low molecular weight proteins (e.g. albumin), as damage = more severe, proteinuria = less selective & large and small proteins are lost.
- Prolonged mild or severe glomerular proteinuria will cause hypoproteinemia (selective hypoalbuminemia or hypoproteinemia).
- Tubular proteinuria = impaired reabsorption and catabolism of the low molecular weight proteins that are normally filtered by the glomeruli; however tubular proteinuria is milder. Often associated with acute renal diseases, but can also be congenital. Do not cause hypoalbuminemia.
- Non-renal proteinuria = contamination of urine with inflammatory exudate or blood may be associated with mild to moderate proteinuria; i.e. proteinuria must be interpreted in conjunction with examination of the urine sediment.
- Test by
- Dipstick for albumin (less sensitive to globulins/Bence Jones proteins
i. [Protein] causes a pH change = colour change
ii. False negative with very acidic urine
iii. False positive with very alkaline urine, drugs/chemicals
- Chemical measurement
i. Precise quantification
ii. Used for urine protein:creatinine ration
iii. SSA = when false positive dipstick reactions are suspected
- Synthesised in the liver
- Small quantities are ingested/absorbed from large intestine
- Hepatic urea cycle synthesis urea from ammonia - the waste product of protein catabolism
- Not found in the faeces
- Appears in the glomerular filtrate in the same concentration as in the plasma
- As it passes along the renal tubules it diffuses passively according to concentration gradients and membrane permeability (influenced by AVP/ADH in the CD).
- Not reabsorbed as efficiently as water
- Rate of reabsorption is related to the rate of flow through the tubules;
1. ↑ rates of urine flow =↓ reabsorption
2. ↓ rates of urine flow = ↑ reabsorption.
- Partially reabsorbed in the DT
- Anything that ↓ the GFR will↑ the blood urea.
- Processes which induce protein catabolism can increase urea production: hemorrhage into the small intestine, fever, burns, corticosteroids, starvation, infection.
- ↑ nitrogen intake in ruminants significantly ↑ urea synthesis in the liver leading to development of mild, prerenal azotemia.
- ↓ urea synthesis may occur with ↓ protein intake or severe hepatic insufficiency.
- Chronic polyuria may result in a ↓ blood urea (washout effect) .'. rate of reabsorption is inversely related to the rate of flow through the tubules
- Urea can be measured in serum, some plasmas and urine
- Some references refer to BUN (blood urea nitrogen); if using SI units this does not affect interpretation, but if converting from mg/dL to SI units it is important to use the correct conversion factor .'. ↑BUN = ↓GFR
- The assay is quite robust and between run CV is expected to be < ≈4.0% with lower values having a CV closer to the upper end of this range.
- Influenced by the diet
- Azostix reagent test strips can be used to get an estimate of the BUN.
1. Useful for ruling out azotemia as they are effective at detecting "normal" blood urea concentrations, but they tend to underestimate value
2. Very low sensitivity, but high specificity