Lab Assessments Flashcards
4 major functions of the nephron are?
- Filtration
- reabsorption
- secretion
- excretion
movement of water and solutes from the bloodstream to the renal tubule (nephron)
- glomerulus
- 20% of plasma volume passing through is filtered
- drive by hydraulic pressure
Filtration
movement of water and solutes from the renal tubule back into the blood stream
- throughout the renal tubule
reabsorption
movement of additional substances from the bloodstream into the renal tubule
- helps with the elimination of wastes
- helps maintain K balance
- helps maintain pH
Secretion
total substance removed in urine
- = filtration-reabsorption + secretion
Exretion
sum filtration rate of all the functioning nephrons
- gold standard for measuring kidney function
- normal = 120/ml/min
- varies according to age- decreases every 10 years after age 40, gender, body size
GFR
uses of GFR?
- identify kidney disease/disorders
- selection of medication dosages
- avoidance of certain medications (nephrotoxic i.e, NSAIDS, antibiotics, antifungals)
- monitior CKD (chronic kidney disease)
- criteria for referral and dialysis
what are GFR levels? when should you refer, when should they be on dialysis?
- Normal GFR > 90
- CKD2 (mild) = 60-89
- CKD3 (moderate) = 30-59 (REFER)
- CKD4 (severe) =15-29
- CKD5 failure) = < 15 (DIALYSIS)
- Produced as the result of normal muscle metabolism
- a product of skeletal muscle contration (dependent on muscle mass of patient)
- excreted entirely by kidney (directly proportional to renal exretory function)
- used to approximate the glomerular filtration rate
- normal serum levels is 0.5-1.5mg/dL
creatinine
what is the relationship beetween serum creatinine and GFR?
Inverse relationship between serum creatinine
- 2x increase in CR = GFR decrease by 50%
- mild elvation = significant dysfunction
- this applies even when values remain within normal limits
- measure of GFR
- normal - 100mL/min (Dependent on age and gender)
- calculated by two means: directly, indirectly
Creatinine clearance
how do you measure CrCL directly?
24 hour urine collection
- both serum and urine needed
- collection does not provide more accurate estimate of GFR than do prediction equations
how do you measure CrCl indirectly?
- uses serum creatinine in
- the cockroft-gault equation
- pharmacokinetic studies use eCrCL therefore it has become the standard for drug dosing
It is is produced in the liver, found in blood and is secreted and reabsorbed by the kidneys
- directly related to the metabolic function of liver
- assuming normal liver function it is an estimate of renal functions
- other variables that effect?- protein breakdown, hydration status, liver failure
- rises quickly in dehydration (faster than CR)
Blood urea Nitrogen
(5-26) mg/dL
increase in nitrogenous waste products (urea and creatinine) diagnosis made on labs alone
Azotemia
symptomatic azotemia (N/V, lethargy)
uremia
classify the duration of kidney failure?
- acute= less than 3 months duration
- chronic= greater than 3 months duration
- good screening test for obstruction and to differentiate acute vs chronic renal disease
- can alo obtain additional information: cysts, the renal size disparity
Renal ultrasound
ways to find the cause of kidney failure?
- Bun/cr ratio
- urine Na
- fractional excretion Na
- urine Sp Gr
- urine osmolality
Evaluate BUN/Cr ratio levels and kidney function
> 20:1 = pre-renal
- GI bleed
- decreased volume
- urine obstruction
< 20:1
- Intra-renal
- often chronic (CKD)
- Compare to serum
- sodium and potassium most common
- random urine Na < 10 suggests dehydration (CHF, liver disease)
- randome urine Na > 20 suggest kidney/adrenal disease
- can be used to calculate FENa (an equation that is helpful to distinguish between pre-renal and intra-renal azotemia)
Urine electrolytes
- Both reflect the kidney’s ability to concentrate urine and relative hydration
- typically specific gravity varies with osmolality
- determined by the number of particles in the urine so:
- higher with dehydration
- lower with hydration
urine specific gravity and osmolality
mainly used for hydration status
- Could be hematuria, hemoglobinuria, myoglobinurina
- presence of erythrocytes on microscope confirms
- false positive is common therefore confirm with microscopy
- false negative is uncommon
Blood (urinalysis)
What is evaluated in a gross evaulation of urine?
color:
- normal varies, influenced by chemical compisition, urine concentration
- can be red- hematuria, food dyes, beets, medications (rifampin)
- red to brown- hemoglobinuria (hemolytic anemia) myoglobinuria (rhabdomyolysis)
- orange- vitamin C, carrots, medications
- green- dyes (Methylene blue), medications(propfol) asparugs
clarity
- clear = norma
- cloudy= “gray area” - coul be normal (precipitated phophate crystals in the urine, could be pyruia (pus/bacterial infection)
- turbid= infection, crystals, protein, etc
Odor
- Urinoid= normal
- pungent may –> UTI
- Fruity/sweet = DKA
- fecal–> Fistula
causes of Acidic pH?
- uncontrolled DM
- starvation
- dehydration
- diet: protein and acidic fruits
causes of alkaline pH?
- salicylate intoxication
- chronic renal failure
- proteus infection
the hallmark of renal disease
two barriers: basement membrane pores and basement membrane negative charge
Proteinuria
Proteinuria classifications?
Transient
- causes?
- temporary change in glomerular hemodynamics causes the protein excess
- follows a benign, self-limited
persistent
- further classifed into 3 categories
persistent proteinuria classification
Glomerular
- may cause MASSIVE proteinuria
- albumin is the primary protein
- many etiologies
Tubular
- malfunctioning tubule cells no longer metabolize or reabsorb the normally filtered protein
- low molecular weight proteins predominate
- rarely exceed 2g/day
overflow
- low-molecular weight proteins overwhelm the ability of the tubules to reaborb filtered proteins
What should be done with asymptomatic patient with mild proteinuria dip?
What about proteinuria on anyone else
if all else is normal on dip
- recheck the urine dipstick
- transient proteinuria is common esp. with fever, exercise, hypothermia, stress, pregnancy, seizure
Anyone else
- get a 24 hour urine
- microscopic examination of the urinary sediment
- urinary protein electrophoresis
- assessment of renal function
- < 3g/24 hours== glomerular or tubular disease (nephrotic)
- > 3g/24h== nephrotic range proteinuria typically GLOMERULAR
- Excretion of 30-150 mg of protein/day
- not detectable by normal urine dip methods, so is a separate test
- affected by hydration status
- indicated by renal tubular disease
Microalbuminuria
- normally filtered by glomerulus and reabsorbed by proximal tubule
- present in urine when load exceeds ability of renal tubule to reabsorb
- sign of DM, cushing’s, liver and pancreatic disease
Glucose
- should not be present on UA
- products of fat metabolism
- may be exepected in: diabetes, starvation, strenous exercise, frequent vomiting, low carb diets, pregnancy
Ketones
- converted by certain bacteria
- this test is specific but not very sensitive (+ result confirms the diagnosis of UTI, (-) result does not rule it out
- bacteria may still be present in the absence
- portion of the stick is sensitive to air
nitrites
- WBC in urine undergo lysis and esterases are released
- maker of the presence of WBCs in urine= pyruia
- sign of UTI
Leukocyte esterase
- could be hematuria, hemoglobinuria, myoglobinuria
- presence of erythrocytes on microscoope confirms blood as cause
- 3+ RBC/HPF in 2 of 3 urine samples
- false positive is common therefore confirm with microscopy
- false negative is common
Blood
what microscopic cells can be seen on urinalysis and what does that indicate?
Squamous epithelial cells
- > 15-20 cells/ hpf
- usually indicates the urine is contaminated
Transitional epithelial cells
- can be normal (bladder, proximal urethra, renal pelvis)
- larger amounts may be suggestive of UTI
Tubular epithelial cells
- desquamation of the tubular epithelium
- suggests significant renal pathology
- indicates infection
- > 100,000/mL reflects significant bacteriuria in an asymptomatic patient
- in symptomatic patient > 100/ml suggest UTI
- the diagnosis should be followed by culture and sensitivity
Bacteria
- Coagulum of protein and the contents of the tubule in which they form
- factors that promote formation: Low urine flow rate, high urinary concentration, low urine pH
- cellular elements determine the type of cast and can hint to certain disease processes
- generally considered a significant finding
Casts
- small #s with exercise, dehydration, stress, pyelonephritis
- may be a normal finding
- from the distal tubules
- protein without cellular inclusion
Hyaline casts
- # of casts increase with severity of disease
- indicated glomerulonephritis: inflammation leads to damage of basement membrane which leads to sudden onset of hematuria, proteinuria, and RBC casts
Erythrocyte (RBC) cast
- Made with WBCs
infectious or inflammatory conditions
- UTI
- Interstitial nephritis
- pyelonephritis
- glomerulonephritis
- renal inflammatory processes
Leukocyte cast
- Seen with renal tubule disease (dilation and destruction of tubules)
- cellular components, if present, are mixed and may include renal tubular epithelial
- seen in ATN, interstial nephritis, eclampsia, nephritic syndrome
Epithelial
- made up of various cell types in final phase of cellular degeneration
- very slow tubular transit time
- severe chronic renal disease (HTN nephropathy)
Waxy/granular cast
- lipid laden renal tubule cells
- indicated nephrotic syndrome, renal disease, hypothyroidsim
Fatty cast
made of various cell types
indicate end-stage renal disease
Broad cast
- square envelop shape
- vary in size
- common with stones
calcium oxalate
- yellow-orange brown in color
- diamond or barrel shaped
- common with gout
uric acid
- may be normal finding
- associated with alkaline urine and UTI
- colorless
- “coffin lid” appearance
Triple phosphate
- colorless
- heagonal shape
- acidic urine
- diagnostic of cystinuria
Cystine crystals
