9- Laboratory Evaluations

omarys's version from 2017-05-30 03:56

Section 1

Question Answer
serum creatinine does not reflect the degree of renal dysfunction in EARLY injury (takes time for it to rise cuz muscle breakdown)
What's 125 ml/min and has no legs?eGFR
Other than dependence on muscle mass/age/etc., what's a drawback of creatinine clearance as an estimate of GFR?creatinine undergoes tubular secretion
Upper limit of serum creatinine? 1.2-1.4 mg% (though it changes from person to person)
Other than low GFR/high meat intake/high muscle mass, when are high lvls of creatinine expected?People on cimetidine or trimethoprim (anti-acid and abx for bladder infections) - these two inhibit tubular secretion
Since urea is filtered and REABSORBED, it gives an _____ of GFR.underestimation
What's normally 20-40 mg% and doesn't give a shit about membranes?serum urea

Section 2

Question Answer
Decreases serum urea expected in (2)liver disease (less bdwn of protein), malnutrition
Increased serum urea expected in (4)(not counting renal insuff.)volume depletion (cuz ^^^ reabs.), corticosteroid tx, GI bleeding, high-protein diet
Can renal insufficiency be accompanied by ELEVATED serum urea?Yea, if e.g. liver disease
What's a better equation for calculating eGFR, MDRD or CKD-EPI?CKD-EPI - accurate throughout entire range of GFR (MDRD not as accurate when GFR is near normal or normal)
4 variables in eGFR equations?sCr, age, gender, race
Cockcroft-Gault, one of us or no?No. Not precise; overestimates GFR in advanced renal failure.
In Cockcroft-Gault, the eGFR is =( 0.85 if woman X (140-age) X massin kg ) / ( 72 X sCr )
One difference bwn AKI and CKD (in terms of etiology)?Injury: due to dehydration, blood loss from surgery/injury, use of medicines... Chronic: due to high BP or diabetes
When do we actually do the good old 24-hour urine collection to assess GFR?In patients with EXTREME Cr levels: DMD/muscle diseases, post amputations, in malnurished or morbid obesity
Drawback of calculating creatinine clearance from 24-hour urine sample?Overestimates GFR (does not take into account the tubular secretion)
Increased secretion of creatinine occurs inadvanced renal injury

Section 3

Question Answer
Some LMW proteins _____ the filtration barrier but _____ _______ in the ______.cross ; are reabsorbed ; PCT (but vast majority of HMW like albumin don't cross)
Order of structures forming filtration barrier (inside>>out)?endothelium (fenestrations) ; GBM ; podocyte
Total protein in urine (per day) is up to ____ mg, most of which is _____, _____ and _____ (these 3 undergo ____).150 ; Tamm-Horsfall ; urokinase ; IgA ; (secretion- that's why their presence is not indicative of glomerular diseases or damaged abs.)
Tamm-Horsfall is AKAuromodulin
Most of the 150 mg of proteins found in urine (in a day's output) get to the urine by ______.tubular secretion (rather than filt.; e.g. uromodulin is MADE in TAL cells and later secreted into tubuli)
Maximal albumin content of urine considered normal?30 mg/day (albuminuria is > 30 mg/day)
Severe albuminura is > _____ mg/day (AKA MACROalbuminuria)300 (bwn 30 and 300- microalbuminuria)
Standard dipstick can detect ______ but not _______macroalbuminuria ; micro-
Microalbuminuria (bwn 30-300 mg/day) reflects an increased risk ofCVD ; diabetic nephropathy
Approx. 50% of dialyzed patients havediabetic nephropathy
Clinical setting of glomerular proteinuria?Glomerular diseases, diabetic nephropathy, hypertensive nephropathy

Section 4

Question Answer
3 types of proteinuria (and the type of proteins in urine)glomerular (HMW) ; tubular (LMW) ; overflow (e.g. in MM- antibodies & free light chains)
The higher the protein content in urine the _______ the color in a dipstick testgreener (but this is only a semi-quantitative test)
Dipstick test only detectsalbumin (so does not help in e.g. MM)
2 methods other than dipstick, one with lower compliance than the other24-hour urine collection (best but low compl.) ; UPCR (or UACR)- better because done in random or timed collection
Other than protein levels and pH, what can the dipstick detect?Leukocyte esterase (+ in UTI) ; nitrites (+ in bacteriuria [but depends on whether there was enough nitrAte initially], esp. enterobacteriaceae)
Dipstick tests can detectdRTA (urine will be alkaline)
T or F- A dipstick test is sufficient to dx hematuria.False. Microscopic observation of RBCs is required.
When there's hematuria (heme in urine) one should include the following situations in the DD:actual erythrocytes (will be sediment if sample is centrifuged) ; hemoglobin (hemolytic anemia) ; myoglobin (rhabdomyolysis)
What is DIRECTLY correlated w/ osmolality of urine?Its specific gravity (1.016-1.022 that of water)

Section 5

Question Answer
An SG of 1.010 (i.e. close to SG of water/plasma) or so indicatesCKD (this is isosthenuria)(an even lower SG is indicative of DI)
Other than all the above (pH, protein, heme, SG, nitrites, leukocyte esterase), the dipstick test also detects these organic compoundsglucose ; ketones (detects only acetoacetic acid)
Plasma glucose level that is a threshold for glucose abs. (above which = glycosuria)180 mg%
Other than DM, what can cause glycosuria?Fanconi synd. (damages PCT so damaged glucose abs.)
Possible contents of a urine sediment RBCs, leukocytes, epithelial cells, casts, lipids, crystals
Possible causes of hematuria (if persistent)Polycystic kidney disease & glomerular disease (more in <40 year-olds) ; malignancies (above 40)
Dx of glomerular hematuriaHematuria + RBC cast (even one RBC cast)(in >40% there are dysmorphic RBCs)
"non-glomerular hematuria ; isomorphic RBCs ; e.g. ureteral bleeding due to stone" is analogous to"glomerular hematuria ; dysmorphic RBCs (acanthocytes) ; e.g. GN)
"Gross hematuria ; visibly red urine ; e.g. in X" is analogous to"microhematuria ; RBCs under microscope only ; e.g. in Y"

Section 6

Question Answer
Most common causes of neutrophilic leukocyturia?UTI (but GN or interstitial diseases also possible)
Most common causes of eosinophilic leukocyturia?acute interstitial nephritis ; renal atheroemboli ; RPGN
What kind of casts are likely in the TAL of the LOH?Tamm-Horsfall mucoprotein casts
The presence of a cellular cast is diagnostic of intrarenal disease (e.g. if RBCs present within matrix of cast >> GN or vasculitis)
Example of infectious kidney inflammationpyelonephritis
Examples of non-infectious kidney inflammationacute interstitial nephritis ; GN
ATN isacute tubular necrosis (causes muddy brown casts)
AKI in hospitalized patients (HA-AKI) is most commonly caused byacute tubular necrosis (ATN)
What can cause acute tubular necrosis?ischemia ; sepsis ; nephrotoxins (acute stuff)
In ATN, the urine will appearmuddy and brown (due to granular casts)
2 types of casts seen in ATNmuddy brown (granular/acellular) and epithelial casts (cellular)
Other than ATN, what condition results in epithelial casts?acute interstitial nephritis
Waxy casts indicatesevere kidney diseases
T or F- Leukocytic casts necessarily indicate infectious kidney disease (pyelonephritis).False. WBCs may be present in casts in any inflammatory kidney disease (including acute interstitial nephritis and even GN)

Section 7

Question Answer
Cellular casts necessarily indicate renal disease, but the presence of acellular casts is considerednormal (TAL cells produce these mucoproteins)
T or F- Granular casts are usually nonspecific.True (unless we're talking muddy brown)
Hyaline casts indicateacidic, concentrated urine (but are nonspecific)
Nephrosis triadproteinuria, hypoalbuminemia, edema
Nephrosis occurs due toincreased glomerular permeability
Mechanism of edema in nephrosishypoalbuminemia = decreased oncotic pressure >> water leaks from vessels
Severe hypoalbuminemia (in nephrosis) may causehyperlipidemia
Fatty casts specifically characterizenephrotic syndrome (casts appear as crosses under polarized light microscopy)

Section 8: General urinalysis

Question Answer
Examples of GN diseases (3)Lupus nephritis ; IgA nephropathy ; ANCA -ive vasculitis
Urinary pattern of GN? (4)Hematuria ; dysmorphic RBCs ; RBC casts ; albuminuria
Urinary findings of HEAVY albuminuria (>3.5 g/day) w/ or w/o (minimal) hematuria and lipid casts indicateNephrotic syndrome
ATN urinary pattern?epithelial casts (+free epithelial cells) ; muddy brown casts (granular casts)
AKI and CKD may shownormal urinalysis w/ few cells (but minimal albuminuria can be present)
2 major etiologies of nephrosis areamyloidosis ; diabetes (= secondary glomerulonephrosis)

Section 9: Evaluation of hematuria

Question Answer
Urinalysis >> hematuria >> Severe proteinuria + presence of dysmorphic RBCs or RBC casts >>> ?Check for ANA (lupus nephritis), ANCA, C3-4 levels, anti-GBM AB's, (sometimes) renal biopsy
Urinalysis >> hematuria >> No severe proteinuria + no dysmorphic RBCs, no leukocytic casts >>> ?Check for IgA nephropathy or TBM disease (+ do urologic evaluation to eliminate stones or neoplasia there)
The most common causes of blood in the urine without any other symptoms (isolated hematuria)?TBM (thinning of GBM) and IgA nephropathy
Transient hematuria may occur during/shortly afterexercise, sex, menses (persistent hematuria occurs in GN along w/ other causes)
Acanthocytes are extremely specific/virtually pathognomonic toGN (esp. if autoimmune)

Section 10: Evaluation of proteinuria

Question Answer
Positive dipstick test for proteinuria >>> ?Quantitative evaluation via 24-hour urine collection or via UPCR (mg/g)
If proteinuria is bwn 30-300 mg/day (microalbuminuria), this is indicative ofearly diabetes, hypertension, early GN
If macroalbuminuria (300-3500 mg/day), check (3)same as for micro- ; transient causes (exercise, fever) ; orthostatic proteinuria
A proteinuria of >3.5g/day suggestsNephrosis
Most common cause of nephrotic syndromeFocal segmental glomerulosclerosis (FSGS), esp in children and adolescents
2nd most common cause of nephrotic syndromeMembranous glomerulonephritis (MGN), affects people bwn 30-50 years old
In transient proteinuria (exercise, fever), there is usuallyless than 1 g protein/day
Orthostatic proteinuria is persistent or transient?persistent (also- protein levels are < 2 g/day)
Orthostatic proteinuria more common inadolescents (3-5% of them; becomes much rarer after age 30)
The dipstick test detects only ______ presence and only ____ _____ _____ (______).albumin ; severely increased proteinuria (>300 mg/day)
While the severity (mg/day) of glumerular and overflow proteinuria may vary widely (and can be quite ___ if there's ___), tubular proteinuria is characterized by ____ protein levels.high ; nephrosis ; low (usually < 2 g/day)