renal-function-tests
DESCRIPTION
UG Physiology LectureTRANSCRIPT
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RENAL FUNCTION TESTS
By doctoroid
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1) Excretory – primary :by urine formation
2) Regulation of volume & electrolyte composition of ECF
3) Regulation of acid-base balance 4) Endocrine function – produce &
secrete: erythropoietin, renin, calcitriol(1,25-DHCC)
5) Site of neoglucogenesis – not primary: in starvations- esp. from glutamine
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collective term for a variety of individual tests and procedures that can be done to evaluate how well the kidneys are functioning.
Primarily reflects two basic mechs.– Glomerular ultrafiltration & Tubular reabsorption/secretion
Practically, divided into 3 groups –1) Analysis of urine & blood2) Specific assessment of renal clearance3) Additional special Tests
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Early detection of possible renal damage & assessment of its severity
Measure progression of the renal impairment & efficacy of corrective therapy
Predict when renal replacement therapy may be necessary
Monitor safe & effective use of drugs, which are principally eliminated through urine.
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A) PHYSICAL :1)Volume > 800-2500 ml/dintake~2.5
L/d Polyuria >2.5L Chronic GN Anuria ,Oliguria2) Appearance > clear Turbid (alkalinity d/t prolonged standing
l/t ppt of Ca/Mg-phosphates,↑phosphate , presence of pus d/t UTI)
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3) Colour> straw/amber-yellow urochrome
Brownish yellow (jaundice) Dark (alkaptonuria) Reddish brown (RBC/Hb/Mb-uria,Porphyria
etc.)
4) Odour> mild aromatic volatile org. acids Unpleasant ammoniacal (prolonged standing) Acidotic fruity (DKA)
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5) Sp. Gravivity & Osmolality > 1.003 to 1.030 & 50-1200 mOsm/kg
(depends on state of hydration of the body) Early morning urine sample(=after
overnight fast)if SG>1.018 & Osm>600 ≡Normal
SG is simplest to measure but unreliable(in presence of HMW substances) for evaluating renal concentrating ability.
SG decreased,increased & fixed(1.010=CRF)
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1) Reaction > mild acidic pH avg.6 (=4.5-7.5)
normal short PP alkaline tide Protein rich diet acidic Vegetable rich diet alkaline also in
type II DTA, UTI by urease producing organisms, Acetazolamide therapy, alkali ingestion.
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2) For abnormal urinary constituents :
I) Proteins > Normal upto 150 mg/d—routinely
undetected Proteinuria albumin predominates By– a) heat & acetic acid test b) Sulphosalicylic acid test c) Esbach’s albuminometer
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II) Reducing Sugars > Normally absent –
glucose/fructose/galactose When renal threshold is exceeded By Benedict’s Test
III) Blood > Normally does not appear By Benzidine Test
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IV) Ketone Bodies > Normally not present By- Rothera’s Test & Gerhardt’s test.
V) Bile salts > Only in early phases of obstructive
jaundice By- Hay’s test & Petenkoffer’s test
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VI) Urobilinogen > N ~1 - 3.5 mg/d ↑ in persistent fevers, hepatobiliary
diseases, haemolytic jaundice By- Ehrlich’s test & Schlesinger’s test
VII) Bile-pigments > Bilirubinuria=↑conj.Bilirubin hep/post-
hep jaun By- Modified Fouchet’s Test
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Imp findings in the urinary sediment includes---
I)Casts >> proteinaceous plugs
Formation favoured by sluggish flow Various shapes c/t tubules in which
formed cellular or non-cellular Types Hyaline, RBC, WBC,
Granular, Broad waxy etc.
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II) Crystals >> Ca-oxalate/phosphate, Triple phosphate--
common May be normally found risk of stone in
future Urate or Cysteine crystals pathologic
III) Cells >> RBCs, WBCs, pus cells, Sq.epithelial,
Tubular epithelial cells
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Strip impregnated with reagents for the substances in question within a urine sample.
By comparing the colour-change(in the paper-squares)with the standardized colour-charts.
Modern dipsticks with multiplied zones: Can detect/measure: Protein, hemoglobin,
glucose, urobilinogen, ketones, leukocytes, specific gravity, and pH
A promising tool everywhere at the level of primary care!!!
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There is no plasma constituent whose conc. depends solely on the functionality of kidneys.
Frequently used are 2 normal metabolic wastes Excreted by kidneys accumulates in renal
dysfunction ↑blood levels
I) Blood Urea Nitrogen >> 8-25 mg% begin to rise only after 50% renal damage
II) Plasma Creatinine >> 0.6 – 1.5 mg% More reliable as BUN is subjected to variations
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Vol. of plasma that is cleared of a substance in unit time, by its’ urinary excretion ml/min
Calculated as: C = UV/P Predominantly determine GFR: Relationship
as—
Correlated more directly with the status of kidney function employed to assess GFR,RPF & RBF
GFR = C
No reabs, No Secret
INULIN
GFR > C Much reabs, No Secret
Gluc, AA, Na+, Cl-
GFR < C No reabs, Much Secret
PAH, Diodrast
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Characteristics of an Ideal Marker : Constant rate of production (or for exogenous
marker can be delivered IV at a constant rate) Freely filterable at the glomerulus (minimal
protein binding) No tubular reabsorption/secretion No extrarenal elimination or metabolism Availability of an accurate & reliable assay For exogenous markers-- safe, convenient,
readilyavailable, inexpensive & physiologically inert
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Various markers used :A) Exogenous >>1) Inulin (gold standard but technically
demanding)2)Non-radiolabelled contrast media (e.g.
Iohexol) 3)Radiolabelled compounds (e.g. 99m Tc-DTPA)
B) Endogenous >>1)Creatinine (marginally overestimates—most
widely used in clinical practice)2)Urea (one of the 1st markers– not used at
present)
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Approximation of bedside GFR with limited accuracy by “Cockroft & Gault formula”
Most widely used & best validated for adultsCcr =(140-Age)x(Wt in Kg)/(Plasma
Creatinine x72) [Correction factor for females = 0.85] value to such formulas for GFR prediction is
likely to increase when an accurate plasma creatinine assay is performed along with inhibition of tubular secretion by cimetidine/probenecid.
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Applying “Fick’s Principle” to kidney :
Amount of a sub excreted by kidney in unit time(UV) =RPF X renal A-V diff. in its plasma conc.(Pa - Pv)
RPF(ml/min) =UV / (Pa - Pv)
Criteria of the marker to be used : Almost totally extracted from plasma with each
passage through kidney Not metabolised/stored/produced by kidney Physiologically inert & easily assayable
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Use of PAH Clearance to measure RPF/RBF:
Cont. low dose PAH inf. plasma conc. Constant All PAH excreted in
urinePv(PAH)=0eliminated ≡> RPF = UV/Pa(PAH) = Clearance of PAH(C-PAH) 10% RPF perfuses non-excretory portionsERPF True RPF = ERPF/0.9 RBF = true RPF / (1 – Haematocrit value)
Normal ERPF = 600-650 ml/min/1.73 sq.mt BSA Approx. RBF = 1200 ml/min
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A) TESTS FOR TUBULAR FUNCTIONS:I) Urine Conc. Test >> Early dinner no food/fluid after 6 PMbladder
emptied @ 7AM discarded specimens collected @ 8 AM & 9AMatleast one should hv SG >1.022 or Osm >850 mOsm/kg
II) Vasopressin test >>No fluid after 6 PM s.c.
ADH(5U)inj.@8PMurine samples collected separately till 9AMatleast one should SG>1.020 or Osm>800
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III) Urine Dilution Test >>Pt. completely empties bladder after overnight
fast drinks 1L waterhourly urine specimens collected for next 4 hrsatleast 700ml will be excreted & atleast one should hv SG <1.004
IV) Urine Acidification Test >>Fasting from midnightcomplete bladder
emptying @morningOral Am.Cl.(0.1gm/kg) with 1L water given hourly urine samples collected for next 6 hrs. atleast one should hv pH of 5.3 or less
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V) Dye Excretion Test or PSP Test>>
Phenolsulphonphthalein(Phenol red)— filtetred & secreted.
600 ml water drink f/b IV 6mg PSPhourly urine samples collected40-60% should be excreted in 1st hr. & another 20-25% should excrete in 2nd hr
Excretion<50% over 2hrs. abnormal Useful for detecting early stage of renal dis.
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VI) Other Sophisticated Methods>>
MICROPUNCTURE techniquesMICROCRYOSCOPIC studiesMICROELECTRODE studies
VII) Renal Biopsy >>Specimen subjected to LM,EM & IFM-studies↑knowledge & better understanding of
renal diseases
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Plain radiograph of abdomen IVPUSG, CT Scan, MRI ScanRadionuclide studies
Strictly speaking, these are not considered to be RFTs, but very useful in present day clinical practice for structural & functional assessment of kidneys.
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