Patterson: Approach to Patients With Renal Disease Flashcards
What hormones are produced by the kidney?
renin
erythropoietin
calcitriol
How do post patients with kidney problems present?
most pts present asymptomatically with abnormal creatinine, GFR, urinalysis, or BUN
SOME pts have blood in the urine, flank pain, or extra-renal symptoms of HTN, edema, confusion
measured or estimated value of # of total functioning nephrons
GFR
What is the normal GFR for a man? For a woman?
men: 130 ml/min
women: 120 ml/min
What happens to GFR with age? What is the average GFR of a 70+ yo patient?
it decreases about 0.75 ml/min per year
a 70+ patient probably has a GFR around 60ml/min
What could cause a decreasing GFR?
loss of nephron function
or
superimposed problem influencing filtration
- possible to have progressive renal disease and a normal GFR
What is the equation used to measure the GFR?
clearance = U(x) * V/P(x)
U(x) = urine concentration P(x) = plasma concentration
a substance 100% filtered by glomeruli- no reabsorption or excretion therefore can estimate GFR
inulin
**not used clinically, because it’s expensive and not practical
Product of muscle and dietary metabolism
Used to estimate GFR if muscle mass and diet remain constant
serum creatinine
What is the relationship between serum creatinine and GFR?
inverse relationship
as SCr increases, GFR decreases
What is the average serum creatinine in men? In women?
What populations have a higher serum creatinine? Lower?
- 13 mg/dl in men
- 93 mg/dl in women
**higher in blacks and young pts
lower in elderly and Hispanics
What are some things that can interfere with the serum creatinine measurement, and make it less reliable?
variations in creatinine production, like amputees or vegetarians
drugs that block secretion of creatinine like H2 blockers
creatinine assays can mistake other compounds for creatinine
large meat meals
This is probably the best equation used to calculate serum creatinine
CKD-EPI
Why is a 24 hour creatinine clearance not totally useful?
it’s complicated to get a complete urine collection over 24 hours
also, it overestimates the GFR by about 10%
When is the BUN elevated?
high protein diet
trauma
hemorrhage (GI bleeds)
When is the BUN low?
low protein diet
liver disease
When will the BUN/creatinine ratio become elevated?
when you’re dehydrated –> increased Na+ and H20 absorption –> increased urea absorption –> increased BUN compared to SCr
What is the normal BUN/SCr ratio? What does a BUN/SCr greater than 20:1 suggest?
15:1
If greater than 20:1, suggestive of pre-renal failure
Measures the percent of filtered sodium that is excreted in the urine
fractional excretion of filtered sodium (FENa)
What does a FENa less than 1% indicate?
pre-renal acute kidney injury
If a patient is on diuretics, FENa is no longer a good indicator of pre-renal AKI. What should you use instead?
FEurea
**FEurea less than 35% suggests pre-renal AKI
What are the 3 parts of a urinalysis?
appearance: note the color and clarity
dipstick evaluation: blood, leukocyte esterase, nitrates, pH, urobilinogen, proteins, ketones, glucose pH
microscopic analysis: cells, casts, crystals, bacteria
If the urine is turbid, what does this suggest?
If the urine is hazy, what does this suggest?
If the urine is milky, what does this suggest?
turbid: infection, crystals, or leukocytes
hazy: mucus
milky: chyluria from nephrotic syndrome with dyslipidemia and oval fat bodies, profolol
If the urine is blue, black or pink, what does this suggest?
inborn errors of metabolism
If the urine is red/brown, what should you do? How do you analyze it after that?
spin it
if there is a clear supernatant on top with a red sediment at the bottom = hematuria (RBCs)
is the supernatant on top is red, there’s hemoglobin or myoglobin in the urine - or beets or food dyes
What is the normal pH of urine? What should it be if you have metabolic acidosis?
4.5-8.5
pH at least 5 in metabolic acidosis
In a UTI with urease producing organisms, what would you expect the pH to be?
well urea –> NH3 will elevate the urine pH to 7+
weight of urine compared with the weight of an equal volume of distilled water.
Used roughly as an estimate of the ‘concentration’ of urine (urine osmolality)
specific gravity
How is the specific gravity different from urine osmolality?
Uosm is affected by the number of particles in the urine
specific gravity is affected by the number and size of particles in urine
**glucose and protein will increase the SG, but not necessarily the Uosm
At what blood glucose level will glucose spill into the urine?
180mg/dl
What kind of ketones would a UA pick up in the urine? When might you see ketones in the urine?
detects acetoacetic acids, but not beta-hydroxybutyric acid or acetone
elevated ketones in starvation and Atkin’s dieters
What protein is measured in a UA?
only albumin
immunoglobulin light chains are not detected
if urine protein is less than 300mg/day, it’s not detected
What should you do if a urine dipstick is positive for protein?
Do a spot urine protein/creatinine ratio
**more practical than a 24 hour urine protein
What components of the blood will cause positive results on a urine dipstick?
RBCs
hemoglobin
myoglobin
**look at microscopic analysis to see if there’s RBCs, if they’re dysmorphic, etc
What is leukocyte esterase in the UA?
it tells you if you have lysed PMNs and macrophages in your urine
What do white blood cells + nitrites in the urine suggest?
E.Coli –> UTI
What do white blood cells, but NO nitrites in the urine suggest?
sterile pyuria
What kind of crystals can you get in the urine?
uric acid: like after lymphoma or leukemia after treatment with chemotherapy (lysed DNA remnants –> uric acid)
calcium phosphate: associated with kidney stones
magnesium ammonium phosphate crystals
If you have RBCs in the urine, what are some common causes? How can you tell if the blood in the urine is non-glomerular or glomerular?
common after exercise, sex, menses, UTI
non-glomerular hematuria: isomorphic rbcs (more likely a GI bleed)
glomerular hematuria: dysmorphic rbcs
If you see acanthocytes in the urine (RBCs with small pieces hanging off), what should you think?
glomerulonephritis
If you see white blood cells in the urine, what’s your differential?
UTI
nephrolithiasis
glomerulonephritis
interstitial nephritis
If you see Eos in the urine, what should you think of?
What is one complication of finding eos in the urine?
interstitial nephritis
you have to use a stain (Wright’s or Hansel’s) to see the eosinophils
What are casts in the urine?
they are cells that have been sloughed from the lumen or have gathered in the lumen, formed to the shape of the lumen, and were excreted - the cells are help together by mucoprotein
What are some pathologic types of casts?
RBC casts –> think glomerulonephritis
WBC casts –> think pyelonephritis or kidney inflammation
granular muddy brown casts –> think acute tubular necrosis
Rapid loss of kidney function resulting in retention of nitrogenous waste products
Injury begins before loss of excretory function manifesting increased creatinine, decreased urine output, acidosis, hyperkalemia, etc…
Occurs in up to 50% of ICU patients
+/- recovery of lost kidney function
acute kidney injury
If you have a stage 1 acute kidney injury, how much will your creatinine increase? What about stage 3?
stage 1: SCr increases 1.5 to 2 fold, or by 0.3mg/dl or more
stage 3: SCr increases by more than 3 fold, or by more than 0.5mg/dl
What are the three categories of acute kidney injury? Where does most acute kidney injury occur?
pre-renal: due to inadequate blood flow to the kidney, so decreased GFR
renal: instrinsic problem in the kidney that damaged filtering mechanism
post-renal: due to an obstruction, which backs up the system and increases filtration pressure
**60% of kidney injury is pre-renal
List some causes of pre renal disease
blood or fluid loss BP meds (low BP) hemorrhage heart attack/heart disease liver failure severe dehydration aspirin, ibuprofen (these meds block COX and prostaglandin formation, so you get more vasodilation)
What are some post-renal causes of AKI?
urinary tract obstruction due to stones, tumor, or prostate enlargement
What are some renal, or intrinsic causes of AKI?
blood clots in arteries/veins of kidney cholesterol deposits in kidney vessels glomerulonephritis infection chemo drugs and antibiotics toxins like alcohol or cocaine
List some meds that can be associated with AKI
ACE inhibitors
diuretics
chemotherapy
NSAIDS
What happens to your urine sodium, urine concentration and urine output in pre-renal AKI?
low volume –> afferent arteriole senses this and increases renin secretion –> RAAS system causes reabsorption of Na+/H20
so urine [Na+] will be low
urine concentration will increase
less urine output
**small volume of concentrated urine
What can be done to quickly recover from pre-renal AKI?
hydration!
What do these lead to?
Decreased circulating volume
Intravascular volume depletion
Reduced renal blood flow
Severe vasodilation
pre-renal AKI
What happens to the BUN/SCr ratio in pre-renal disease?
What happens to the urine sodium?
What will the FeNa be like?
increased BUN/SCr because there is reduced flow, which allows for greater reabsorption of creatinine
urine sodium will be less than 20
FENa will be less than 1%
Disease of the small to large vessels of the kidney
Disease of the glomeruli (primary or secondary)
Nephritic –inflammatory with active urine sediment – casts, cells, dysmorphic RBCs
Nephrotic- >3.5 grams protein/24 hrs. Very minimal cells and casts
Disease of the tubules and interstitium
Intrinsic (renal) AKI
inflammatory with active urine sediment – casts, cells, dysmorphic RBCs
nephritic
greater than 3.5 grams protein/24 hrs. Very minimal cells and casts
nephrotic
If you see buddy brown casts, what should you think of?
acute tubular necrosis
If you see eosinophils, RBCs and leukocyte casts, what should you think of?
acute interstitial nephritis
If you see hematuria, proteinuria, RBC casts, and dysmorphic RBCs, what should you think of?
acute glomerulonephritis
If you suspect a post-renal AKI, such as nephrolithiasis, BPH/prostate cancer, or a pelvic tumor, what should you do?
ultrasound of the kidneys
