Evaluation of the Kidney Part 2

What is polyuria?

Production of excessive amounts of urine

What are the mechanisms of polyuria?

1. Lack of ADH production

2. Distal tubule/collecting duct cells cannot respond to ADH

3. Must be a concentration gradient between tubular fluid and interstitium (MUST have osmolality of the interstitum > osmolality of the tubular fluid)

-Solute diuresis

-Reduced medullary interstitium osmolality

When can solute diuresis occur?

-When the kidneys are functioning normally but are presented with increased solute (i.e. DM)

-When there are decreased numbers of functional nephrons and as a result there is an increased solute load on the available functioning nephrons

Why does liver failure cause PU/PD?

Decreased liver function --> decreased urine production --> decreased amount of urine in interstitum --> decreased resorption --> increased urine volume

What are the stages of CKD?

1. Decreased renal reserve (50% GFR normal capacity)

2. Chronic renal insufficiency (25-50% function)

3. Chronic renal failure (

What would you see on physical exam and in bloodwork for a patient with decreased renal reserve?

Clinically healthy: Not azotemic or polyuric but susceptible to insult

What would you see in bloodwork in a patient with chronic renal insufficiency?

Azotemia, anemia, decreased concentrating ability (but not yet isosthenuria)

What would you see in bloodwork in a patient with chronic renal failure?

Azotemia, anemia, decreased concentrating ability, electrolyte imbalance, clinical signs of uremia

What would you see in bloodwork in a patient with end-stage renal disease?

Terminal uremia signs and oliguria or anuria

What are the major criteria for diagnosis of CRF?

-Evidence of decreased GFR --> azotemia

-Evidence of decreased concentrating ability --> Isothenuria

What causes polyuria in Chronic renal disease?

1. More solute presented to remaining functional nephrons

2. Medullary hypertonicity is not maintained

3. Damaged cells less responsive to ADH

What blood values are indicative of renal insufficiency or failure?

-Azotemia

-Inappropriately low USG (isothenuria)

What blood values are indicative of chronicity in regards to renal failure?

-Anemia

-Hypocalcemia (typical in dogs, cats, ruminants)

-Hypercalcemia (Equids)

-Clinical findings including duration of signs

Is acute renal failure reversible or irreversible?

Can be either

Does the degree of azotemia differentiate between chronic or acute kidney disease?

No, but the rate of increase in UN and creatinine is more rapid in acute disease

What causes acute renal failure?

Toxins, ischemia, infection

How does acute renal failure impact urine volume?

-Kidneys may filter little blood --> oliguria or anuria

-No time for compensatory hypertrophy of healthy nephrons

How does acute renal failure impact USG?

-Variable:

-Concentrated if formed prior to insult

-Isothenuric if after

-NOT expected to be hyposthenuric

What is the most common mechanism for addition of protein to urine? (Important)

-Hemorrhagic (from anywhere in the urinary tract)

-inflammatory proteinuria (inflammation causing exudation of plasma proteins into the urinary tract)

Does proteinuria lead to hypoalbuminemia? (Important)

No

What is functional proteinuria?

A transient mild increase in urine protein content (can be due to exercise, fever, seizures, stress)

What is overload proteinuria?

Increased plasma concentration of small proteins that pass through glomerular filtration barrier and exceed capacity for tubular resorption (Hemoglobin, myoglobin, immunoglobulin light chains)

Does overload proteinuria lead to hypoproteinemia? (Important)

No

What is tubular proteinemia?

Proximal tubular injury causing failure to reabsorb small proteins

What is tubular proteinuria usually associated with?

Acute renal tubule damage (nephrotoxic agents or ischemia)

Does tubular proteinuria result in hypoproteinemia? (Important)

No

What causes glomerular proteinuria?

-Damage/disruption to the glomerular filtration barrier (immune complex deposition, amyloid deposition, inflammatory cells releasing cytokines)

-Increased permeability to large and/or negatively charged proteins

What is the first protein to be seen in urine due to glomerular proteinuria?

Albumin

What does glomerular proteinuria lead to?

Selective hypoproteinemia

What can progressive glomerular disease lead to?

Tubular damage and tubular proteinuria, loss of nephrons --> azotomia, renal failure

What can you see with severe glomerular damage?

The entire nephron may become nonfunctional which can cause signs of renal failure

What can severe, persistent proteinuria lead to?

Nephrotic syndrome:

-Proteinuria

-Hypoproteinemia

-Hypercholesterolemia

-Ascites or edema

What must you do before attributing proteinuria to glomerular or tubular disease? (Important)

Must rule out pre and post-renal sources

-Hemorrhage

-Hemoglobinuria

-Myoglobinuria

-Inflammation

How much protein can be found in concentrated urine in animals with no evidence of urinary tract disease?

Up to 1+

When is glomerular disease suspicious (in terms of USG and proteinuria)?

If no evidence of non-glomerular sources of proteinuria AND

-1+ urine protein in dilute urine

-2+ protein in concentrated urine

-And/or hypoalbuminemia with no other cause apparent

When is UPC most useful?

When pre and postrenal sources of protein are ruled out

What is UPC?

Protein/creatinine ratio: An index of the amount of protein regardless of urine concentration

When will UPC be increased?

With any increase in protein

When should UPC be used?

When trying to identify source of protein