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UG Physiology Lecture
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RENAL FUNCTION TESTS
By doctoroid
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
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
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.
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)
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)
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)
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.
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
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
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
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
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.
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
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!!!
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
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
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
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)
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.
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
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
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
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
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.
VI) Other Sophisticated Methods>>
MICROPUNCTURE techniquesMICROCRYOSCOPIC studiesMICROELECTRODE studies
VII) Renal Biopsy >>Specimen subjected to LM,EM & IFM-studies↑knowledge & better understanding of
renal diseases
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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