18: Renal Function Test and Urinary Analysis - Fang Flashcards
creatinine is nearly 100% _____, minimally re-absorbed
filtered
Because of it’s filtration, reabsorption pattern, it is a useful marker of GFR
Baseline values dependent on MUSCLE MASS
Not a perfect test – inaccurate in mild impairment, no utility in CKD, individual variability
Rise in BUN may indicate …
- Kidney injury/reduction in GFR
- ↑nitrogen load (UGI bleed, high-protein diet)
- Dehydration (less plasma = ↑ concentration)
- Steroid use
Low BUN – liver failure, urea cycle defects
BUN:Cr greater than 20 suggests ________
BUN:Cr less than 20 suggests ___________
PRE-RENAL
INTRA-RENAL
distinguish the origins of an acute kidney injury; not diagnostic, but helps direct work-up
GRF estimation
Most common/easiest – serum creatinine
- -Accuracy affected by mass, baseline, other factors
- -Requires correction equations (MDR, Cockcroft-Gault)
More accurate
- -Inulin excretion – requires injection, monitoring
- -24h urine creatinine – difficult execution
*** normal UA =
no blood, no nitrites, no ketones, no glucose, no leukocyte esterase
clues from dip-stick urinalysis
Specific gravity – hydration status, renal concentrating capacity
Proteinuria – mild, moderate, severe
* Test detects higher MW proteins (albumin)
Infectious changes – leuk esterase, nitrites
Blood – hematuria, rhabdomyolysis
* Test detects blood PROTEINS, not RBC’s
hematuria dx
- IgA nephropathy
- Post-infectious nephropathy
- Hereditary nephropathy (Alports syndrome)
- Thin basement membrane disease
- Malignancy
- Nephrolithiasis
- Infection
- Foley trauma
Should ALWAYS be done when dip-stick is abnormal
Urine Microscopy
Normal microscopy – no “casts”, no RBC, no WBC, few or no epithelial cells
abnormal urine microscopy findings **
WBC – infection, sterile pyuria
Epithelial cells – may indicate sample contamination
RBC – correlate with dip-stick blood
Casts- cells coated with tubular prtns
**“Muddy brown” granular Hyaline casts **RBC **WBC Fatty, “maltese cross” Pigment
“Muddy brown” granular - Acute Tubular Necrosis
Hyaline casts - Dehydration/volume depletion
RBC – glomerulonephritis, vasculitis, renal infarct
WBC – pyelonephritis, interstitial nephritis, post-strep GN
Fatty, “maltese cross” – nephrotic syndrome
Pigment – hemolysis, rhabdomyolysis, liver disease
*** know all of this!! Muddy brown cast = RBC cast = WBC cast = Eosinophils = Dipstick blood pos, no RBC = *No protein on dip, proteinuria on UPC ratio =
Muddy brown cast = ATN
RBC cast = GN
WBC cast = pyelo or AIN
Eosinophils = AIN, contrast
Dipstick blood pos, no RBC = Rhabdomyolysis
*No protein on dip, proteinuria on UPC ratio = Multiple myeloma (SSA can be added to turn dipstick pos)
Reasons to perform CT over ultrasound
To diagnose nephro- or urolithiasis
Body habitus prevents quality ultrasound images
Further delineation of lesions seen on ultrasound
Angiography necessary
diagnostic criteria for AKI
Creatinine rise greater than =0.3mg/dL in less than 48hrs
OR increase of greater than =50%
OR UOP (urine osmotic pressure) less than 0.5mL/kg/hr for greater than =6hrs
** 3 categories of AKI based on the anatomic or functional location of the problem
Pre-renal
Post-renal
Intra-renal
*** Most common cause of AKI in the ambulatory patient is ________
pre-renal
causes: *Volume depletion/dehydration Heart failure Shock Renal artery stenosis Medications – diuretics, NSAID’s (constrict afferent), ACEI/ARB (dilate efferent)
The underlying pathopysiology of pre-renal AKI is DECREASED HYDROSTATIC PRESSURE IN THE GLOMERULUS
