UG Physiology Lecture

1. RENAL FUNCTION
TESTS
By
doctoroid

2. 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

3.  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 & blood
2) Specific assessment of renal clearance
3) Additional special Tests

4.  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.

5.  A) PHYSICAL :
1)Volume > 800-2500 ml/dintake~2.5 L/d
 Polyuria >2.5L Chronic GN
 Anuria ,Oliguria
2) Appearance > clear
 Turbid (alkalinity d/t prolonged standing l/t
ppt of Ca/Mg-phosphates,↑phosphate ,
presence of pus d/t UTI)

6. 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)

7. 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)

8. 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.

9. 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

10. 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

11. 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

12. 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

13. 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.

14. 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

15.  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!!!

16.  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

17.  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 &
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

18.  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, readily
available, inexpensive & physiologically inert

19. 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)

20.  Approximation of bedside GFR with limited
accuracy by “Cockroft & Gault formula”
 Most widely used & best validated for adults
Ccr =(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.

21. 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

22.  Use of PAH Clearance to measure
RPF/RBF:
 Cont. low dose PAH inf. plasma conc. Constant
 All PAH excreted in urinePv(PAH)=0eliminated
 ≡> RPF = UV/Pa(PAH) = Clearance of PAH(C-PAH)
 10% RPF perfuses non-excretory portionsERPF
 True RPF = ERPF/0.9
 RBF = true RPF / (1 – Haematocrit value)
 Normal ERPF = 600-650 ml/min/1.73 sq.mt BSA

23. A) TESTS FOR TUBULAR FUNCTIONS:
I) Urine Conc. Test >>
Early dinner  no food/fluid after 6 PMbladder
emptied @ 7AM  discarded specimens
collected @ 8 AM & 9AMatleast one should hv
SG >1.022 or Osm >850 mOsm/kg
II) Vasopressin test >>
No fluid after 6 PM s.c. ADH(5U)inj.@8PMurine
samples collected separately till 9AMatleast
one should SG>1.020 or Osm>800

24. III) Urine Dilution Test >>
Pt. completely empties bladder after overnight fast
drinks 1L waterhourly urine specimens
collected for next 4 hrsatleast 700ml will be
excreted & atleast one should hv SG <1.004
IV) Urine Acidification Test >>
Fasting from midnightcomplete bladder emptying
@morningOral 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

25. V) Dye Excretion Test or PSP
Test>>
 Phenolsulphonphthalein(Phenol red)—
filtetred & secreted.
 600 ml water drink f/b IV 6mg PSPhourly
urine samples collected40-60% should be
excreted in 1st
hr. & another 20-25% should
excrete in 2nd
hr
 Excretion<50% over 2hrs. abnormal

26. VI) Other Sophisticated
Methods>>
 MICROPUNCTURE techniques
 MICROCRYOSCOPIC studies
 MICROELECTRODE studies
VII) Renal Biopsy >>
 Specimen subjected to LM,EM & IFM-studies
 ↑knowledge & better understanding of renal

27.  Plain radiograph of abdomen
 IVP
 USG, CT Scan, MRI Scan
 Radionuclide studies
 Strictly speaking, these are not considered to be
RFTs, but very useful in present day clinical
practice for structural & functional assessment of
kidneys.