Renal (kidney) assessment tests & specimen collection

Exam 1

What is the purpose of a kidney clearance test?

Measures how efficiently the kidneys filter waste product from blood plasma mL/min (where it is neither reabsorbed or secreted)

What are the two clearance tests used on urine?

• Inulin

• Creatinine

Inulin is a clearance test used on urine. What is inulin? What would you not want to really use it for?

• Fructose polymer that is not usually in the body (exogenous)

• Isn’t reabsorbed or secreted

• Not good for glom filtration

Creatinine is a clearance test used on urine. What is creatinine? What part of the nephron does it use?

• waste product from muscle

• Produced by the body (endogenous)

  • Can be passed through glom but not absorbed by tubules

Tests the glom filtration rate (GFR) in mL/min : compares the amount of creatinine in blood to that in a 24hr urine sample

What are some disadvantages of doing a creatinine clearance check?

Some of it is secreted by the tubules

• High meat diets can give false readings

• Muscle-wasting disease gives VERY false readings (since GFR checks muscle breakdown byproducts)

What is the formula for creatinine clearance? What is the reference range for GFR? What about plasma creatinine?

C = (UV/P) * (1.73/SA)

U = Urine creatinine (mg/dL)

V = Volume of urine (mL/min)

P = Plasma creatinine (mg/dL)

Reference: 80-125 mL/min

Plasma: 0.8 - 1.3 mg/dL

What are the two clearance tests used on plasma?

• Cystatin C

• Beta2-microglobulin

What is Cystatin C? What filters it? Does it get reabsorbed or secreted? Is it present in urine?

A protein that is produced by all nucleated cells.

• Filtered by kidney (glom)

• Not secreted but IS reabsorbed & broken down by renal tubules

  • Not in urine

Not affected by muscle mass

What is beta2-microglobulin? What filters it? Who should this test not be used on?

• Antigen produced by HLA

• Filtered by Kidney (glom) → when function declines B2M is increased in blood.

• Should not be used with immunologic disorders or malignancy

What is the first sign of renal (kidney) disease? How is it assessed and what are the reference ranges for serum & urine.

• Loss of renal disease

• Assessed via osmolality ( [particles in sol] )

Serum: 275-300 mOsm

Urine: 500-1400 mOsm

What should the ratio of urine to serum be? What should it be after controlled fluid intake?

• Normal: 1:1

• Fluid: 3 (urine) : 1 (plasma)

What two diseases create the inability to reabsorb water in the kidney?

• Neurogenic Diabetes Insipidus → decreased secretion of ADH

• Nephrogenic Diabetes Insipidus → adequate ADH production but kidneys have ADH resistance

What are two ways to test for Neurogenic and Nephrogenic diabetes?

• Fluid deprivation: Fluids given till 6pm (stimulates ADH)

• ADH injection: collect urine & serum at 2 & 4 hrs

If Urine:Serum is 3:1 after adding in ADH, what diabetes is this? Interpret.

If Urine:Serum is 1:1 after ADH has been added, what diabetes is this? Interpret.

• Neurogenic Diabetes → Adding ADH allowed for an increase of [urine], which means the kidneys do respond to ADH properly, but the body isn’t producing enough

• Nephrogenic Diabetes → Adding ADH doesn’t change [urine], indicates kidney resistance to ADH

What does the kidney (overall) form? What is it’s main job?

• Forms plasma ultrafiltrate

• Water & filtered substances are reabsorbed

What is the composition of urine (%)? What is the primary substance found in the solute and what % is that?

95% water

5% solutes

• 2% of this is urea → made in liver as waste product of protein

• 3% → other solutes (creatinine, uric acid, salts - Cl-, Na+, K+)

What is the range of normal urine expulsion from the body?

600mL - 2000mL

What is Oliguria? Provide the range.

Dehydration → due to loss of water through vomiting, diarrhea, sweating, burns

Urinating <400mL/day

What is Anuria? What does this indicate?

No urine production → extensive damage to kidneys or decreased renal function

What is Nocturia? What disease can this indicate someone has?

Increased nighttime urination.

• Diabetes

What is Polyuria? What diseases is this a sign of?

Excretion of excessive amounts of urine

• Diabetes mellitus, diabetes insipidus, diuretics

What is Tm? What is the Tm and renal threshold for glucose?

Tm: solutes absorbed per minute

Glucose Tm: 350mg/min

Glucose renal threshold: 160-180 mg/dL ← once this is exceeded, glucose appears in urine

What does Diabetes mellitus cause an increase of and why?

• Increase in plasma glucose due to defect in production/function of insulin

  • Kidney does NOT reabsorb excess glucose → therefore appears in urine

What does the body do to remove glucose from the body once it can no longer be reabsorbed? Describe what the urine will look/be like?

Glucosuria: increases water secretion to remove glucose ← Polyuria

• Urine will look dilute (pale yellow) with high specific gravity

What is Diabetes insipidus caused by? What does the urine look like and why?

• Caused by decreased production/function of ADH

Urine: pale/dilute b/c water is NOT reabsorbed into body with low specific gravity b/c the body is mainly expelling water due to lack of ADH ← Polyuria

What should a urine container look like/be? How do you label it? Preservation?

Container: clean/dry/clear, leak proof

Labeling: name, medical #, date & time of collection ← all labeled on SIDE of container, not lid

Preserved: in fridge

What is a random collection (for urine)? What is it used for?

Urine collected at random time.

Used for Drug testing

What is a first morning urine sample used for? Is this the best sample to take?

Uses: Pregnancy test, Urinalysis (ex. UTIs, diabetes)

• Ideal specimen b/c very concentrated

What is a fasting urine sample used for? When is it collected?

Uses: checks for diabetes/glucose/ketones & monitors baseline urine analytes

Collection: Second voided urine to avoid first urination (which would contain food metabolites from prior day)

What is a X-hour postprandial urine sample used for? When is it collected?

Uses: 2hr glucose postprandial Test, urine glucose test

Collection: 1-3 hours after eating

What is a 24hr urine sample used for? How/when is it collected?

Uses: checks diurnal variation → monitors fluctuation of hormones, proteins, and electrolytes

Collection: Start at 7am and void 1st urine → then place all urine from rest of day into container → at 7am of day 2 add this last urine into container, then done.

How is a catheterized urine sample collected? When is it performed?

Catheter is inserted into bladder

• Performed if clean-catch cannot be done

if culture is needed, do culture first to prevent urine contamination

What is a midstream urine catch sample used for? How is it collected?

Uses: checks for UTIs & ketones (usually reabsorbed, bad if in urine)

Collection: Patient cleans self & urinates into sterile container → void a bit into toilet, then into container

How is the suprapubic aspiration urine collection done?

Completely sterile → needle inserted through abdomen into bladder

What are the three levels to how urine can look?

Urochrome: pale - bright yellow → hydrated

Uroerythrin: pink/slightly brown “brick dust” → dehydrated

Urobilin: orange/brown/dark brown → extremely dehydrated

What can cause orange, red, green, brown, and black urine?

Orange: dehydration, Vit. C, medications → potential problems: liver/bile

Red/pink: beets, blood, hemoglobin/myoglobin → poten. prob.: hematuria, UTIs

Green: Pseudomonas, biliverden, food, medications → pot. prob.: UTI

Brown: homogenostic acid → pot. prob: Liver disease, muscle breakdown

Black: Melanin → pot. prob.: melanoma

What are some nonpathological reasons urine may be turbid?

• Epithelial cells in urine (non-clean catch)

• Mucus in urine

• fecal contamination

• crystals

• precipitation of amorphous rates/phosphates after refrigeration

What are some pathological reasons urine may be turbid?

• Bacteria

• Proteins

• WBCs

• Yeast

• abnormal crystals

What is specific gravity?

Measures the density of urine to the density of water. (Checks how well the kidneys dilute or concentrate the urine)

What is a urinometer?

historical way of checking urine concentration.

• Not accurate for high protein and glucose

• Not used in clinical lab

What is a refractometer? What is the reference range?

Used to check urine concentration using specific gravity.

• Uses a refractive index (compares velocity of light in urine with velocity of light in solution

Reference range: 1.003 - 1.030

What is the specific gravity for isosthenuric urine? Hyposthenuric? Hypersthenuric?

Isothenuric: 1.010 (same as plasma ultrafiltrate)

Hyposthenuric: <1.010

Hypersthenuric: >1.030

Urine can have different smells. What causes a foul/ammonia-like smell? Fruit/sweet? Maple-syrup? Sulfury? Mousy smell? Rancid smell?

Foul/ammonia-like: infection

Fruity/sweet: diabetes/ketones

Maple-syrup: maple-syrup disorder

Sulfur: Asparagus

Mousy: Phenylketonuria

Rancid: Tyrosinemia