Water intake normal values:
Water intake (acute: decreased, chronic: increased, in general)
generally: 20-40 ml/kg body weight/day
maximum: 80 ml/kgBW/day - dog, 40 ml/kgBW/day - cat calculating: general dog (30 ml/ kg bw): 1 l/day
- small dog (10 kg bw): 3 dl/day (300 ml/day)
- general cat (3 kg): 1 dl/day (100 ml/day)
Horse: 20-30l/day
Cattle: 20-40 l/day (in milking cows water intake can exceed 100 l - for the production of 1 l of milk, approx. 4 l of water intake is necessary)
Sheep, goat: 1-2 l/day
Swine: 3-8 I/day
General normal urine output:
General normal urine output (in general daily urine output is somewhat less, than the water intake, since some water output occurs with faeces and evaporation from the lungs):
dog: 20-40 ml/kg body weight/day
cat: 10-20 ml/kg body weight/day
horse: 5-15 l/day
cattle: 20-40 l/day
sheep, goat: 1-2 l/day
swine: 3-8 l/day
Examination of the glomerular function can be done by?
- Blood urea (BUN=blood urea nitrogen) concentration in blood plasma
- Creatinine concentration in blood plasma
- Plasma urea (mmol/l) / plasma creatinine (umol/l)
- changes in plasma urea and creatinine concentration NOT due to enal disease (diagnostic problems)
- Creatininine clearance
- Urinary total protein concentration
- Urinary total protein / urinary creatinine ratio
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Blood urea (BUN=blood urea nitrogen) concentration in blood plasma:
- function and character
- Urea is an end product of the Ornithine-cycle in order to detoxify NH3 absorbed from the intenstines (NH3 is the breakdown product of proteins)
- Energy of three ATP molecules is needed for the whole cycle.
- Urea is a non toxic, but osmotically active molecule, which expresses serum or urine osmolality
- Because it is a small molecule it can penetrate thorugh membranes.
- Ure is filtered thorugh the glomeruli and reabsorbed from the tubules.
Blood urea (BUN=blood urea nitrogen) concentration in blood plasma:
Azotaemia/Ureamia
Azotaemia: Prerenal, renal or postrenal
- accumulation of nitrogen containing protein breakdown products in the blood (eg. Urea)
Ureamia: Prerenal, renal or postrenal
- severe increase in the level of nitrogen containing protein breakdown products and toxins in the blood, leading to obvious clinical signs (Anorexia, depression, vomitting, diarrhea, lethargy, stomatitis, gastritis, etc.)
Blood urea (BUN=blood urea nitrogen) concentration in blood plasma:
Determination
Each biochemical test determining urea concentration starts with splitting urea into two NH3 molecules by urease enzyme according to the formula:
urea + H2O +O2–> urease –> 2 NH3 + CO2 .
Method 1) Urea-colour test
Method 2: Enzymatic urea method
Blood urea (BUN) concentration in blood plasma:
- Method 1: Urea colour test
- NH3 in water forms NH4+
- NH4+ forms grenn colour in alkalytic pH with Na-hypochloride and salycilic acid.
- The green colour can be measured spectrophotometrically on 600 nm wave length.
- it is an end point reaction and it is linear (the result is reliable) till 24.97 mmol/l urea concentration
Blood urea (BUN) concentration in blood plasma:
Method 2) Enzymatic urea method
2 NH3 + 2-alpha keto-glutaric-acid + 2NADH + H+ –> GLDH (glutamate-dehydrogenase) –> 2 L-glutamic-acid + 2 NAD+ +2H2O
- Change of NADH + H+ –> 2 NAD+ causing light emission change and it is measurable on 340 nm wave length. (the speed of absorbancy decrease is in correlation with urea concentration of the blood sample)
- After 30 seconds of preincubation, the extinction change is measured within 1 min.
- It is a kinetic reaction and it is linear till 65 mmol/l urea concentration.
- Normal value: 8-10 mmol/l
Causes of increased blood urea conenctration:
- Prerenal factors
- increased nitrogen (protein) intake: “overproduction azotaemia”
- in ruminants: poor energy status in the rumen (urea is an important indicator of carbohydrate and protein balance) Les mer på et annet Fc
- Increased intestinal protein catabolism (intestinal NH3 production by bacteria): Urea is an indicator of small intestinal bacterial overgrowth (SIBO) similarly to vitamin B12 decrease (increased utilisation by bacteria) and folic acid increase (increased production by bacteria)
- Intestinal or gastric bleeding: blood in the intestines typically increases urea concentration in the blood and it can cause significant diagnostic problems
- Haemolysis: hemolysis of RBC cause a marked increase in blood urea concentration. Increased catabolsim of the tissues own protein: energy deficiency (eg due to decreased carbohydrate intkae), widespread neoplastic processes, high fever, endogenous overproduction or iatrogenic overdose of catabolytic hormones (thyroxine, glucocorticoids)
- Decreased blood perfusion of the kidneys (prerenal axoteamia): shock, hypotension, dehydration, cardiac failure, hypoadrenocorticism (addison disease), thromboembolism or strangulation of the renal artery.
Prerenal factor for increased urea concentration:
Poor energy status in the rumen
Urea is an important indicator of carbohydrate and protein balanace
- in ruminants 90% of the protein intake is catabolised (to NH3) then resynthesisied by the ruminal microorganisms.
- 10% of the protein intake is “by-pass” protein, which is passed to the intestines then digested and absorbed.
- the microorganisms need a quite amount of energy (usually from carbohydrates) for the protein resynthesis.
- Urea is a small molecule and it is excreted through the salivary gland, ruminal wall, kidney and udder too.
- as a result of energy deficiency in ruminants the rumina micro-organisms can not produce enough protein so the catabolised protein (end product is NH3) is passed to the bowels and absorbed from there or absorbed directly from the ruminal wall, and transported to the liver via the portal vessels.
–> increased NH3 load forces the liver to produce increased amount of urea (until liver function is normal), which is measurable in the blood and milk. In milk the urea concentration is always lower than in plasma: 2-3 mmol/l
- Energy deficiency without liver function disorder in ruminants, cause increased urea concentration in blood and in milk, increased ketone concentration in blood, urine and milk: and decreased glucose concentration in blood and increased total lipid concentration in the blood.
Causes of increased blood urea conenctration:
- Renal factors
Kidney function: primarily glomerular function, acute and chronic renal failure “retention azotaemia”
- decreased amount of functionally active nephrons (chronic renal failure, renal fibrosis “retention azotaemia”
- decreased tubular filtration “tubular reabsorption azotaemia”
- marked increase can be expected in case of an ordinary daily protein intake (100 g/day - human) when GFR decreases to 1/4 of the normal
Causes of increased blood urea conenctration:
- postrenal factors
- inhibition of urine flow thorugh the lower urinary tract, due to the occlusion of the pelvis, urether or urethra: “retention azotaemia”
- rupture of the kidneys, urether, urinary bladder, or urethra: “uroperitoneum”
Causes of decreased blood urea conenctration:
- impared liver function: decreased urea synthesis in the liver cells from NH3, leading to increased NH3 level
- Haemodilution (hyperhydration)
- decreased protein intake (starvation, anorexia)
Creatinine concentration in blood plasma
- function and character
- Creatinine is an important constituent of muscle energy stores. creatinine is utilised to form creatin
- Creatin is bound to a phosphate group, which being released, provides energy for the muscle cells. From creatin sarcosin is fored in the muscles.
- A constant amount of creatinine is released into the blood from the muscle if the muscle mass is cnstant (constatnly 2% of total creatin is broken wodn to creatinine every day).
- Creatinine is generally filtered thorugh the glomeruli and is not reabsorbed from the tubules
- as there is no tubular reabsorption and it is released from muscles, its plasma concentration and filtration is normally constant, creatinine is a good indicator of the glomerular function.
Creatinine concentration in blood plasma
- Determination:
Method 1) Jaffe method
Commonly used, colorimetric, kinetic
- Creatinine forms yellow-orange complex with picric acid in alkalytic pH.
- the complex contains ion bonds.
- speed of complex formation is dependent of the creatinine concentration.
- other components of the plasma (like glucose, ascorbic acid, ketone bodies, etc) are also able to react with picric acid.
- there is a competition among these molecules, but the speed of the reaction with creatineine is the highest.
- after 10 sek of preincubation the change of colour formation is measured by spectophotometer within 2 min on 492 nm wavelength.
- it is a kinetic reaction and it is linear till 442 umol/l.
- the result is highly influenced by hemolysis and jaundice.
Creatinine concentration in blood plasma
- Determination:
method 2: enzymatic method
creatinine + H2O –> creatininase –>creatin
creatin + H2O –> creatinase –> sarcosin + urea
sarcosin + O 2 –> sarcosin-oxydase –> glycine + HCHO + H2O2
H2O2 + 4-aminoantipyrine –> peroxydase –> red kinon derivate + 4H2O
- Reagent 1 and sample should be preincubated for 5 minutes together and measured (E1)
- then Reagent 2 (4-aminoantipyrine, creatininase, peroxydase) should be added and measured (E2) on 555 nm wave length.
- The change should be measured for standard and sample.
- Concentration can be calculated by the formula:
(sample(E2 -E1) / standard (E2 -E1)) x Standard concentration = Sample concentration
- It is a kinetic reaction and it is linear till 1770 µmol/l.
- Normal value : 50-200 µmol/l
Blood creatinine depends on:
- Meat content of the diet (increased or decreased): some creatinine is formed during digestion of eat, but mostly the high protein diet has a long term indirect effect on blood creatinine conenctration thorugh increased the body´s muscle mass
- state of muscles: muscle necrosis (causes increased creatinine level), Cachexia (causes decreased creatinine level)
- Kidney-gomerulus function (decreased filtration rate)
Normal value of Plasma urea/ Plasma creatinine ratio, and wen do we measure it?
We use this ratio if both parameters are increased in the blood and we are interested in the cause of the increase
Normal value: 0.1-0.06
Plasma urea (mmol/l) / plasma creatinine (umol/l)
- causes of the increase when it is >0.06
Prerenal kidney failure - decreased blood supply of the kidney:
- shock, dehydration, hypotension
- obstruction (thromboembolism) or compression of kidney (glomerular) arteries
- vasoconstriction of kidney (glomerular) vessels
Postrenal causes:
- ureter-, urethra-, urniary bladder- (neck) obstruction, compression
Extrarenal causes:
- not renal increase of urea concentration in blood plasma
Plasma urea (mmol/l) / plasma creatinine (umol/l)
- causes of the increase when it is <0.06 (0.02-0.05):
Renal, sometimes postrenal causes
since many factors influence the plasma urea concentration, the pasma:creatinine ratio has limited reliability and give only orientative suggestion about the cause.
Changes in plasma urea and creatinine concentration NOT due to renal disease (diagnostic problems)
- High urea, low, normal creatinine:
High urea:
- increased protein intake
- gastrointestinal bleeding
- fever (increased protein catabolism)
- tetracycine, steroid treatment
- haemolysis
- necrotic processes
- hyperthyroidism (increased protein catabolism)
- catabolic drugs (amphetamine)
Low, normal creatinine:
- Cachexia
- chronic muscle atrophy
Changes in plasma urea and creatinine concentration NOT due to renal disease (diagnostic problems)
- Low, normal urea, high creatinine
Low, normal urea:
- liver failure, portosystemic shunt
- polyuria-polydypsia
- low protein intake
- anabolic steroids
High creatinine:
- inflammation of muscles (myocarditis, rhabdomyolysis)
- rhabdomyosarcoma
- muscle trauma
- increased meat intake
Physiological/Pathological value of the TP:creatinine ratio:
Physiological value: <1
Pathological value:
- >1: it means that a 20 kg dog passes at least 30mg/kg/day or 1g/day proteins
- 1-5: the proteinuria is usually prerenal.
–> in some renal diseases (glomerulonephropathy) protein loss increases and the creatinine excretion does not show change, the value of the ratio becomes increased.
–> in case of other renal diseases (tubulonephropathy) protein loss does not show change, the creatinine excretion becomes decreased, the value of the ratio is also increased (>5)
- Normal value: <0.078 in dog
- if the ratio is more than 0.131, there is a pathological proteinuria.
Analysis of tubular function:
- Basic test
- Analysis of enzymuria
- urinary sediment analysis
- water deprivation test
- tubular clearance examinations
