Renal system- diagnostics

Glomerulus

in renal artery

in renal vein

• 1. glomerular function
• 2. glomerular/tubular damage
• 3. tubular function

*estimate gross kidney function via blood and urine

#1 DM and HTN: more than 50% of ESRD

#2 CV disease

Infection ->glomerulonephritis (strept pyogenes)

genetic -> PCKD

• -nonspecific malaise
• -HA
• -N/V
• -flank pain
• -dysuria (burning), oliguria (little), anuria (none)
• -Discolored/malodorous urine
• -rash
• -HTN
• -unexplained electrolyte disturbance (elderly)
• -abnormal labs

• -Nitrogen retention
• -elevated BUN
• -prerenal, postrenal, renal

-can live for awhile

• -Urea retention
• -Occurs with symptomatic ESRD

-needs dialysis

• -reduced renal function for >3mo
• -most common
• -results from multiple conditions: DM, HTN

• -problems occur before kidney
• -causes decreased blood flow to kidney
• (stenosis, artherosclerosis, HTN)
• -decreases filtration rate
• -prdominant cause of azotemia

• -damage to renal parenchyma
• -glomerulonephritis
• -PCKD
• -tubular necrosis

• (excludes renal vein)
• -occurs after kidney; usually obstruction in ureters, bladder, urethra

waste product from hydrolysis of creatine and phosphocreatine in muscle

• -filtered at glomerulus
• -secreted at proximal tubules

kidney function decline = increase in serum, decrease in urine

• -naturually higher in males
• -more sensitive than BUN

-Always compare to previous values

-levels double with 50% decrease in GFR

• -creatine supplements
• -muscle wasting
• -temporarily w/marathon runners

Blood urea nitrogen

• -product of protein and nucleic acid catabolism
• -evaluates glomerular function
• (urea synthesized in liver and >90% excreted through kidneys)

-more volatile than creatinine; need to use ratio

• -increase with impaired kidney function
• -declines with liver failure or malnutrition
• -normal <20 mg/dL

• -varies daily
• -affected by blood in GI tract, protein intake, hydration
• (dehydration increases BUN)

• increased in prerenal/postrenal azotemia

• -to differentiate prerenal/postrenal azotemia from renal azotemia
• -ratio is used w/abnormality, not alone

Normal = 10:1, and levels rise proportionally

• Prerenal azotemia = 20:1 +
• BUN increases faster w/ bigger increase (decr. renal perfusion)

Renal azotemia = 10:1; elevation together

Early postrenal obstructions = 20:1; early, acute rise; can evolve into renal azotemia from pressure damage, then ratio returns to 10:1

glomerular filtration rate

• -direct measure of renal function
• -body fluid cleared by kidneys per time unit using estimated body surface area

• -based on creatinine levels
• -good early indicator of disease w/changes

-varies according to age, sex, body size (muscle mass)

• based on creatinine values, age, gender, race
• (females have 25% less; naturally higher in AA)

• -Decrease precedes onset of kidney failure
• -more sensitive and specific than BUN
• (good to use w/HTN and DM as early predictor)

-presistent decrease is diagnostic criterion for CKD

-naturally decrease with age

<60 = onset of CKD; follow closely; increased risk of CV disease

<30 = get on meds; refer to nephrology

<15 = need dialysis; risk factors for other diseases

*treat these levels seriously; no variation like with BUN and creatinine

if you can't get good eGFR

• -based on muscle mass
• -tends to overestimate GFR
• -sensitive test to warn of kidney failure

• -depends on accurate 24hr urine collection
• -affected by large amounts of meat ingestion

uses weight, age, serum creatinine

• -evaluates physical and chemical properties
• -can evaluate multiple disease states

-use clean-catch and chemstick

• -2hrs
• or
• -24hrs

• -can evaluated urine output
• -can confirm presence of abnormality

pigmented by urochrome (product of metabolism)

• -yellow variations = state of hydration
• -amber variations = urine concentration or specific gravity

fruity (acetone) = diabetes (ketosis)

fould odor = UTI (urea splits to ammonia)

• clarity of specimen
• normal = clear

• cloudy:
• -normal if change in urine pH
• -WBCs, RBCs, bacteria
• -clear, hazy, cloudy, turbid, milky

• -measures kidney's ability to concentrate urine
• -measures density of urine against density of distilled water

• 1.001 - 1.010 Dilute
• 1.010 - 1.025 Normal
• > 1.025 Concentrated

order urine osmolality to confirm

• -renal tubules maintain acid-base balance
• -tubular secretion of H+ and NH4+

• normal = 4.0-8.0
• avg = 5.0-6.0

Negative = normal

• Hematuria
• Hemoglobinuria

-on urine dipstick, not distinguishable btn hematuria and hemoglobinuria

• RBCs in urine
• -majority of disorders within urinary tract
• -UTI, kidney stones, infection

• Hemoglobin in urine
• -majority of disorders outside urinary tract that cause hemolysis

-sick pt; ER setting

-measures albumin and globulins

• -may be first sign of renal disease
• (even before symptoms)
• -single most important indication of renal disease

-order 24hr urine for protein if (+) on dip

• -precursor to albumin
• -ordered on DM pts

• -detects very small amount of protein in urine
• -early detection for kidney disease

• ordered anually = type 2 DM
• ordered anually = type 1 DM after 5 yrs

-if (+), confirm in 3mos

diagnosis of nephropathy

-ACE-I or ARB can slow/prevent

Normal = negative

check serum glucose level if positive in urine

Normal = negative

-particularly important with Type 1 to evaluate ketoacidosis and diabetic coma

-can also appear with Atkins diet

Normal = negative

• -nitrate converted to nitrite by bacteria (gram (-) bact)
• -usually used to screen UTI
• -elderly, symptomatic pts, pregnant pts

Normal = negative

• -esterase released by the leukocytes into the urine
• -positive = UTI

• false-positive from:
• -vaginal discharge/infection
• -bleeding
• -heavy mucus

• nitrites
• leukocyte esterase

Normal = negative

• -even trace amounts are abnormal
• -early sign of liver disease or biliary obstruction

-increases with any disease that causes increased serum conjugated bilirubin

• -bilirubin transformed through bacterial enzymes into urobilinogen in intestines
• -colorless
• -trace amounts are normal

• -very sensitive test for liver dysfunction
• -elevation = liver disease or hemolytic d/o
• -absence = obstruction of bile duct

Normal = no casts

• WBC cast = renal parenchymal infection
• Broad/waxy cast = collecting tubule dysfxn/acute renal failure

RBC cast = hemorrhage in nephron

-to diagnose bacterial UTI

-ordered at urine C&S

-direct measure of kidney function

Normal = 1200mL in 24hrs

(range 600-2500mL)

decreased ouput

100-400 mL/24hrs

severely decreased

<100 mL/24hrs

increased output

>3000 mL/24hrs