Renal Lab Eval Flashcards
Kidney’s fxn?
- excretion of waste products of metabolism
- regulate excretion of water and solutes (Na, K, and H), through changes in tubular reabsorption or secretion
- secretes hormones: renin, prostaglandins, and bradykinin
erythropoietin, Ca2+, phosphorus, (and calcitriol)
Sxs of kidnney disease?
- gross hematuria, flank pain
- edema, HTN, signs of uremia
- many pts are asx, only sign is elevated serum creatinine or abnorm uirnalysis
Azotemia?
- elevated BUN and/or creatinine, buildup of abnormally large amounts of nitrogenous waste products in the blood
Oliguria?
- urine output of less than 400 ml a day, or less tahn 20 cc/hr
Anuria?
- hardly any output at all
- less than 100 mL/day
Causes of pre-renal failure?
- volume contraction (dehydration)
Causes of intrinsic renal failure?
- arteriolar damage (acute HTN)
- glomerulonephritis
- ATN (acute tubular necrosis)
Causes of post-renal obstruction?
- ureteral obstruction
- bladder outlet obstruction
What does the GFR tell us? normals? influenced by?
- sum filtration rate of all fxning nephrons
- men norm: 130 mL/min
- women: 120 mL/min
- influenced by: age, sex, body size, RBF and HP in glomerulus
How can the GFR be measured?
- CrCl
- urea clearance
- inulin clearance - 100% filtered, gold std for GFR
What is CrCl? Normals?
- endogenous substance used to assess GFR
- men (Up to 40): 107-139 ml/min
- women: 87-107
- overestimates true GFR by up to 40% because of active tubular secretion of creatinine
How does GFR correlate with kidney disease?
- level of GFR has prognostic indications but isn’t the exact correlate to loss of nephron mass
- stable GFR: doesn’t imply stable disease
- some pts with renal disease may go unrecognized b/c of normal GFR
What is BUN (blood urea nitrogen)
- urea nitrogen is what is formed when protein breaks down
- normal range: 6-20 mg/dL
- many drugs can effect the BUN
- usually measured with creatinine to monitor kidney fxn
What causes an increase in BUN?
increases when protein is broken down and more ammonia forms:
- renal disease
- excessive protein breakdown (catabolism - tissue necrosis)
- very high protein diet
- GI bleeding***
- burns
- tetracycline
- fever
- decreased GFR: less BUN presented at glomerulus to be removed from the blood
slower transport time through PCT allows more reabsorption
What causes a decrease in BUN?
- liver disease (liver unavailable to convert ammonia to urea then the BUN will decrease and the ammonia increases)
- starvation
Where does BUN come from?
- protein is cleaved from the AA and a nitrogen is left behind so it takes up 3 H+ to form ammonia
- NH3+ is then processed through the liver to become urea
- when urea enters to blood stream it is called BUN
- then it is excreted by the kidney
How does decreased GFR lead to increased BUN?
- 2 ways
1. decreased flow through glomerulus
2. slower transport time allows more BUN to be resorbed at level of PCT
What is creatinine?
- formed from normal breakdown of muscle
- more muscle mass the higher creatinine
- lower the muscle mass the lower the creatinine (normal reduction in creatinine as a person ages and loses muscle mass)
Normal range of creatinine?
- waste product of protein breakdown excreted by the kidneys
- normal range: men - 0.8-1.4
women: 0.6-1.2 - 50% loss of renal fxn is needed to increase serum creatinine from 1-2 mg/dL
- used in ratio with BUN to determine types of azotemia
In what situations is creatinine increased?
- renal failure
- diet: increased digestion of meats
- meds: ACEIs, diuretics, NSAIDs
- muscle disease/breakdown: muscular dystrophy, rhabdomyolysis
- blockage at sites in DCT that allow for active secretion
- decreased GFR as there is less creatinine presented at glomerulus to be filtered out
when would creatinine be decreased?
- pregnancy: normal occurence
- range in pregnancy: 0.4-0.6 mg/dL (increased volume)
What happens to creatinine with a decreased GFR?
- increases
- instead of creatinine being reabsorbed in the tubules like BUN with a decreased GFR the creatinine is just dumped out
- in the DCT creatinine is actively secreted from the body to be eliminated by the kidneys
- this active secretion at the DCT can be blocked by drugs such as cimetidine and trimethoprim therefore increasing serum creatinine
Normal range of BUN/creatinine ratio?
- normal: 10-20.1
- elevated: greater than 20.1
- increased ratio in a low flow (low BP) state
- BUN/serum creatinine
When is BUN/creatinine ratio increased with normal creatinine?
- prerenal disease (decreased renal perfusion)
- catabolic state with increased tissue breakdown
- GI hemmorrhage
- high protein intake
- certain drugs: tetracycline, steroids
When is BUN/creatinine ratio increased with elevated creatinine?
- postrenal disease (obstructive uropathy)
- prerenal disease superimposed on renal disease
When is decreased BUN/creatinine (less than 10:1) with decreased BUN occur?
- acute tubular necrosis (intrarenal disease)
- low protein diet, starvation, severe liver disease
- repeated dialysis
- SIADH
- pregnancy
When is BUN/Creatinine decreased with increased creatinine?
- rhabdomyolysis
- muscular pts who develop renal failure
Normal values for Na and K?
- Na+: 135-145 mmol/L
- K+: 3.8-5.5 mmol/L
Normal values for anions?
- chloride: 98-106 mmol/L
- bicarb: 21-28 mmol/L
- total CO2: 23-30 mmol/L
substances that are normally reabsorbed in the kidneys?
- Na+
- K+
- urate
- chloride
- Ca2+
- phosphate ions
- glucose
- AAs
What substances are normally secreted in the kidneys?
- H+
- K+
- urate
Sodium reabsorbtion in the kidneys? Impt of Na+?
- freely filtered at glomerulus
- 60% reabsorbed isotonically in PCT
- reabsorbed in loop of Henle
- reabsorbed in DCT, secondary to aldosterone effect
- normall daily Na excretion balances daily intake (body needs for Na can be met by as little as 500 mg/day)
- Na+ is extracellular ion, doesn’t move freely across the membrane, impt in cardiac and neuro fxn (too low - seizures)
What is hyponatremia primarily due to? Correction?
- most common electrolyte disorder
- primarily due to intake of water that can’t be excreted
- excess Na+ loss relative to water loss occurs via renal or extrarenal routes
- therapy: correct underlying problem, Na+ and fluid replacement
When does hypernatremia occur?
- occurs when there is an excessive loss of water, relative to Na+
- causes include renal and extrarenal routes
- therapy: approp fluid replacement combined with use of diuretics to rid body of excess Na+
Gains and losses of K+?
- major cation in intracellular compartment
- gains: normally derived from dietary sources
balance usually maintained in healthy persons by daily intake of 50-100 mEq - losses: kidneys are the main source of K loss (80-90% lost in urine, remainder lost in stool or sweat)
Why is it so impt to be efficient at regulating K+?
- small change (1-2% of EC volume) can lead to dangerously high serum levels
- norm: 3.5-5 mEq/L
What is K+ homeostasis dependent on?
- pH (acid-base disturbance causes K+ shifts b/t fluid compartments, in acidosis K+ levels go up as bringing K+ out of cells into blood - diabetic ketoacidosis)
- renal fxn including effects of diuretics aldosterone and renal parenchyma
- GI fluid losses (excessive K+ loss with V/D)
What does hypokalemia result from?
- K+ shifting to ICF w/o change in total amt of K+ in the body
- depletion of body stores (diuretic therapy w/o K+ replacement)
When does hyperkalemia occur?
- acidosis
- from cellular damage (fever, hemolysis, rhabdomyoylsis - K+ leaking out of destroyed cells)
- renal and adrenal diseases
- meds (ACEIs)
- artifical hyperkalemia: hemolyzed blood specimens, thrombocytosis or leukocytosis
When does hypochloremia occur?
- excessive loss of Cl-: GI losses DKA mineralocorticoid excess salt-losing renal diseases high bicarb levels
When does hyperchloremia occur?
- metabolic acidosis
- lower GI losses (diarrhea)
- mineralocorticoid deficiency
Bicarb filtration?
- filtered freely in glomerulus
- 85% reabsorbed in proximal tubule
- 15% reabsorbed in distal tubule
Ways that urinalysis can be useful?
- detect systemic disturbances: endocrine abnormalities metabolic disturbances - detect intrinsic kidney/urinary system disorders: kidney disease UTIs
Diff ways a UA can be collected?
- fresh voided urine: first morning specimen random specimen post-prandial (after meal) - clean catch (midstream) urine - catheterized specimens - timed urine collections (24 hr)
Best method of collecting urine sample?
- first morning void is best (most concentrated)
- record collection time
- type of specimen (clean catch)
- analyzed within 2 hours of collection (for best results: within 1 hr)
- free of debris or vaginal secretions
- storage/preservation reqd if not tested within 1 hr: refrigeration - 5 c, preservative tablets for transport
When is a supra-pubic needle aspiration indicated?
- when pt is unable to void, or there has been trauma to urethra
3 types of examination?
- physical
- chemical
- microscopic
What are the physical characteristics of the urine specimen?
appearance (visual exam):
- color: normal varies (colorless to yellow to amber)
depends on concentration of solute (urochrome and urobilin)
- turbidity: normal=clear, cloudy when crystals or large amts of cells present
- odor
- volume: 750-2500ml in 24 hrs (avg of 1500 mL)
oliguria: output of less than 400ml/day
- anuria: less than 100 ml/day
Examples of different odors?
- ammonia like (urea splitting bacteria)
- foul, offensive: old specimen, pus or inflammation
- sweet: glucose
- fruity: ketones
- maple syrup like: maple syrup urine disease
Examples of different colors of urine and what they could mean?
- colorless: diluted urine
- deep yellow: concentrated urine
- yellow-green: bilirubin
- red: blood/hemoglobin
- brownish/red: acidified blood (Acute GN)
- brownish-black: homogentisic acid (melanin)
Turbidity?
- looking at cells or crystals most likely if turbid
- cellular elements and bacteria will clear by centrifugation
- crystals dissolved by a variety of methods (acid or base)
- microscopic exam will determine which is present
what are all of the elements of the chem analysis?
- specific gravity
- pH
- protein
- glucose
- ketones
- bilirubin
- urobilinogen
- blood
- leukocyte esterase
- nitrite
How is the chem analysis usually done?
- by a dipstick
- chemical presence produces color changes
- have to read at appropriate time interval from when reagent dipstick is dipped into urine
What is specific gravity, what does it mean?
- reflects the relative proportions of dissolved solid components to total volume of specimen: degree of concentration or dilution of urine, measures concentrating abilities of the kidney
- expected values:
range: 1.003-1.030
usual results: 1.010-1.025
highest value is 1st morning specimen: greater than 1.020
What does a low specific gravity mean?
High specific gravity?
- low: diabetes insipidus - abnormal ADH
- tubular damage and renal anomalies
- well hydrated
What does a high SG mean?
- DM (glucose, protein, ketones concentrating the urine)
- adrenal insufficiency
- hepatic disease
- CHF
- excessive sweating or other loss of water (diarrhea, vomiting, fever)
pH values?
- urine acidity due primarily to acid phosphates
- pH of less than 7= acid urine
- pH of gerater than 7= alkaline urine
- expected values: normal kidneys produce urine with pH varying from 4.5-8
- freshly voided urine: 6
Acidic urine?
- high protein diets
- meds
- uncontrolled diabetes or other causes of metabolic acidosis
Alkaline urine?
- normal, post-prandial physiology
- diets high in veggies, milk, and other dairy
- meds
- UTI
What makes up the protein in the urine? Expected results?
- majority is globulins (Lower MW than corresponding serum globulins)
- 1/3 albumin
- tamm-horsfall mucoprotein: normal urinary protein not found in plasma (matrix to make casts)
- up to 2.5 mg/dL
- expected results:
avg 40-80 mg protein excreted per day
100-150 mg/day in WNL therefore concentration in random urine is 2-8 mg/dL
***proteinuria is the single most impt indicator of kidney disease
Albumin will show up in urine for what reasons?
- strenous exercise
- emotional stress
- pregnancy
- infections
- glomerulonephritis
- neonates (1st week)
Globulins will show up in urine for what reasons?
- glomerulonephritis
- tubular dysfunction
Hemoglobin will show up in urine for what reasons?
- hematuria
- hemoglobinuria
Fibrinogen will show up in urine for what reasons?
- severe renal disease
Bence Jones proteins will show up in urine for what reasons?
- myeloma (there will be alot of protein)
- leukemia
How is protein detected in the urine?
- microalbuminuria: not detected on normal dipstick
requires use of special dipstick for microalbuminuria less than 50 mg/dl - proteinuria: generally requires 24 hr urine collection for total protein
start in am with first void and collect for 24 hrs keeping specimen in the refrigerator - total amt of protein excreted is measured
Causes of benign proteinuria?
- functional changes: (increased metabolic rate) high fever, CHF, strenuous exercise, cold exposure
- orthostatic: occurs when upright (common in adolescence)
What is an early indicator of kidney disease?
- microalbuminuria: 30-100 mg/24 hrs
What constitutes proteinuria?
- greater than 100 mg in 24 hrs
When does glucosuria occr?
- whenever blood glucose level exceeds the renal threshold
- ability of renal tubule to reabsorb, only can absorb 180 mg/dl
- condition may be benign (renal glycosuria) or pathological: DM
- renal glycosuria occurs after heavy meals and emotional stress
What is ketonuria the result of?
- of fatty acid metabolism which occurs when there is:
inadequate carbs in the diet
and when there is a defect in carb metabolism
Clinical significance of ketonuria?
-DKA in DM
- restricted carb diet in assoc with:
fever, anorexia, GI disturbances, fasting/starvation, neuro disorders, anesthesia
expected values of bilirubin? clinical significance of bilirubinuria?
- reflects serum levels of conjugated (direct) bilirubin
- negative urine test is normal
- concentration in urine is normally less than 0.02 mg/dL
- clinical significance of bilrubinuria:
hepatocellular disease, biliary obstruction or any disease that increases the amt of conjugated bilirubin - can be an early indicator of disease, even before jaundice is present
How is urobilinogen produced?
- bilirubin is conjugated in the liver and secreted into the bile
- bile enters intestinal tract where bacterial action converts bilirubin to urobilinogen
- excreted in feces or reabsorbed into portal circulation
- removed by the liver and/or excreted in the urine
Normal urinary excretion rates?
clinical significance of increased urobilinogen?
- normal rate: 1-4 mg/24 hr
- clinical significance of increased urobilinogen:
pernicious anemia
liver disease: hepatitis, cirrhosis, CHF - urobilinogen is decreased/absent in obstruction of bile duct
What is hematuria? Hemoglobinuria? Normal test?
- hematuria: intact red cells in the urine
- hemoglobinuria: free hemoglobin in the urine
- myoglobinuria - also produced positive test
- normal: neg test for blood
Clinical significance of hematuria or hemoglobinuria?
- hematuria: renal disease, infections, neoplasm, trauma
- hemoglobinuria: any of the above plus transfusion reactions, hemolytic anemia, paroxyysmal nocturnal hemoglobinuria (PNH), severe burns, various poisonings
What is leukocyte esterase? Clinical significance?
- neutrophilic granulocytes release esterases into urine when present
- normals: no WBCs, negative esterase
- clinical significance of + test:
pyuria (presence of WBCs in urine) - bacteriuria/UTI
Nitrites?
- nitrates are normal urinary constituent but nitrites are NOT
- some gram neg bacteria are nitrate reducers producing nitrites, therefore, the presence of nitrites in the urine indicates bacteriuria
What nitrate reducing organisms are most comonly found in urine?
- E. coli - 72%
- klebsiella/enterobacter - 16%
- streptococcus faecalis - doesn’t reduce nitrate
What are frequently seen elements in microscopic analysis?
- crystals
- cells
- infectious agents
- casts
Procedure of examining microscopic elements?
- centrifuge 10-15 ml urine 5-10 min at 1500-2000 rpm
- decant/discard supernatant urine
- examine under low (10x) and high (40x) magnifications
Causes of acidic urine crystals?
- uric acid (kidney stone, gout)
- amophous urates
- bilirubin
- cystine (rare)
- cholesterol (rare)
- leucine (rare)
- tyrosine (rare
Causes of neutral urine crystals?
- calcium oxalate
- hippuric acid
- triple phosphate
Causes of alkaline urine crystals?
- calcium carbonate
- ammonium biurate
- calcium phosphate
What are the cellular elements of the UA?
- RBC
- WBC
- epithelial cells: renal tubular cells (round, slightly larger than WBC), transitional cells (flat, cuboidal, columnar), squamous (large flat cells)
Infectious agents on microscopic exam?
- yeast (urinary moniliasis): haephea (tree branch)
candida albicans (and others)
especially in pts with diabetes - parasites: trichomonas, schistosoma haematobium
How are casts formed?
- decreased urinary flow
- increased concentration of solutes
When are RBC casts formed?
- acute inflammatory or vascular disorder in glomerulus causing renal hematuria
- may be the only manifestation of acute glomerulonephritis
When are WBC casts formed?
(think infection)
- these indicate kindey inflammation
- acute pyelonephritis
- interstitial nephritis, proliferative glomerulonephritis
How do RBC casts appear under microscope?
- muddy brown color
When are hyaline casts observed in the urine?
- these are only slightly more refractile than water and have a transparent, empty appearance
- hyaline casts may be observed with small volumes of concentrated urine or with diuretic therapy and are generally nonspecific
- clear on microscopic exam
When are granular casts seen in the urine?
- these are coarsely and finely granular
- leakage and aggregation of proteins
- coarse, deeply-pigmented granular casts are considered characteristic of ATN
Waxy casts?
- last stage in degeneration of granular cast
- waxy casts are nonspecific and may be observed in a variety of acute and chronic kidney diseases
Significance of cellular casts?
getting casts: coming from kidneys - RBC/erythrocyte casts, leukocyte casts, and bacterial casts
- if you are just getting cells: single erythrocytes, single leukocytes, single bacteria
this could be coming from kidney down through bladder
What are common findings in acute tubular necrosis?
dipstick:
- decreased SG
- for blood
- positive for protein
- microscopic:
renal tubular epithelial cells
pathological casts (intra-renal problem)
Common findings in acute glomerulonephritis?
dipstick:
- blood: increased
- protein: increased
microscopic:
erythrocytes (dysmorphic)
erythrocyte casts
mixed cellular casts
Common findings in chronic glomerulonephritis?
dipstick:
decreased SG
increased blood
incread protein
microscopic: pathological casts (broad waxy casts, RBCs)
Common findings in acute pyelonephritis?
- dipstick:
trace proteins
positive nitrites
positive L.E.
microscopic: bacteria leukocytes leukocyte, granular and waxy casts (intra-renal) renal tubular epithelial cell casts
common findings in nephrotic syndrome?
- a lot of protein (++++)
microscopic:
oval fat bodies (dumping protein)
fatty casts
waxy casts
Common findings in eosinophilic cystitis?
- blood
- microscopic: numerous eosinophils (Hansel’s stain)
- no significant casts
Common findings in urothelial carcinoma?
- blood
microscopic:
malignant cells on urine cytology (urine sample should be submitted separately to cytology, void or 24 hr sample)
