abeer renal function testsamr renal function tests renal block

7/27/2019 Abeer renal function testsAmr Renal Function Tests Renal Block

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Renal Function

Tests

BY

Dr. Amr A. AminDr. Abeer Ahmed


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Functions of the kidney

Regulatory function

Excretion of waste products:

Endocrinal function

Metabolic Function


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NEPHRON FUNCTIONS

GLOMERULAR FILTRATION: glucose, amino acids,creatinine, urea, phosphates, uric acid

TUBULAR REABSORPTION: bicarbonate,phosphates, sulfates, 65% of Na and water, glucose, K,amino acids, H ions

TUBULAR SECRETION: hydrogen and potassium,

remove acids (hydrogen) to maintain appropriate acidbase balance, potassium,


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Glomerular filtration Of one-fifth of the cardiac output flows through the two kidneys

(i.e. a flow rate of 10001200 ml/min), the glomerulus filters 125-130 ml/min (GFR) of an essentially protein-free, cell-free fluid,

called glomerular filtrate.

The rate of filtration across this membrane is governed by

multiple factors including renal blood flow and the integrity of theglomerulus membrane.

Glomerulus has multiple small pores through which chemicals

are filtered from the blood but excluding any substance with a

molecular radius more than 4 nm (e.g. cellular blood component).

Moreover, substances that are neutral or have positive charge are

more likely to pass through the pores of the glomerulus than

substances that are negatively charged (e.g. albumin).


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Tubular reabsorption and secretion

The filtrate flows through the renal tubules, where water and

solutes may be reabsorbed, secreted, synthesized, or

metabolized.

Sodium is exchanged in the presence of the hormone

aldosterone and water is exchanged in the presence ofantidiuretic hormone (ADH).

Exchange of solutes may occur as active transport, which

occurs against the concentration gradient of the chemical and

uses energy, or as passive transport, which occurs with the

concentration gradient of the chemical.


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Renal Function Tests: Serum BUN and creatinine ( convenient & insensitive ) Clearance rate (Creatinine )

eGFR

Full urine examination

Osmolarity measurement in plasma and urine Water depriviation test

Acid load test

Urine analysis:specific proteinuria, glycosuria,aminoaciduria


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Urinalysis (UA)

Fresh sample = Valid sample

Physical

Chemical

Microscopic examination


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Chemical Examination To perform the chemical examination, most clinical laboratories use commercially prepared test strips

upon which a chemical reaction occurs between urine absorbed and the chemicals of the pad to developthe color of the pad within seconds to minutes.

The degree of color change for each pad can be read and interpreted manually or by automatedinstruments

.

The degree of color change on a test pad can also give an approximation (semiquantitative analysis) ofthe amount of substance present and reported as (from 1+ to 4+) .

The most f requently performed tests using reagent test strips are:

specific gravity ,

pH ,

protein ,

glucose ,

ketones ,

blood ,

leukocyte esterase ,

nitrite ,

bilirubin ,and

urobilinogen .

Somereagenttest strips also have a test pad for ascorbic acid [vitamin C.


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Urine Composition1- Urine Volume

Normal: more than 500 ml/day

Polyuria: high Pr. Diet/high urea/diuresis/ Tea-Cola, andcoffee/diuresis/ high salt intake/ high fluid intake/ DM/highosmosis/high H2O secretion/ Diab. Inspidus/ Ch.R.F/ Hypertension/high GFR/high filtration).

Oliguria: dehydration/ low fluid intake/sweating/vomiting/diarrhea)Hemorrhage and shock/low B.pressure/low GFR/ Acute R.F and

Urinary obstruction/ Fever).

2- Color

Normal: Amber yellow ,colorless or faint yellow.

(Urochrome+Urobilin) Red color: Haemoglobinuria or Haematuria

Black color after exposure to light: Alkaptinuria (Oxid ofhomogentisic acid)

Milky: Pyuria (Pus cells).


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Urine Composition3- Specific Gravity (SG)

Specific gravity, is actually a physical characteristic of the urineindicates how much concentrated the urine is, it can be measuredusing a chemical test.The normal urine may range from 1.010 1.030

There are no "abnormal" specific gravity values.

SG may be as low as 1.002 in case of :

Drinking of excessive quantities of water in a short period oftime/gets anIV-fluids )infusion of large volumes of fluid).

The upper limit of the test pad, SG of 1.035, indicates a concentratedurine, one with many solutes in a limited amount of water.

Knowing the urine concentration helps health care providers decideif the urine specimen they are evaluating is the best one to detect aparticular substance. For example, if they are looking for very smallamounts of protein, a concentrated morning urine specimen wouldbe the best sample.


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4- pH The glomerular filtrate of blood plasma is usually acidified by renal

tubules and collecting ducts from a pH of 7.4 to about 6 in the final

urine. Depending on the acid-base status, urinary pH may range from as low

as 4.5 to as high as 8.

Some substances may be precipitated forming crystals in alkaline

urine.

Another substances may be precipitated forming crystals in acidicurine.

5- Appearance: Normal: clear/ Abnormal: Turbid may bedue to ppt of P/Mg/Ca (Alkaline pH) OR due to

UTI/Haematuria/Pyuria/Chyluria(Fat absorbed/ crystals of oxalates orureates)

6- Odor: Normal: aromatic due to volatile org. acids. / Abnormal:acetone in case of DM/ bad odor in case of pyuria


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Under normal circum. All glucose is reabsorbed by active mechanism.

Hence, Glucose is normally not detectable in urine.

Glucosuria results from either :-

An excessively high glucose concentration in the blood, such asmay be seen with people who have uncontrolled diabetesmellitus.

A reduction in the renal threshold. Sometimes the thresholdconcentration is reduced and glucose enters the urine sooner,at a lower blood glucose concentration ( Eldery)

Pregnancy (38%) . (Gestational Diabetes)

Some other conditions that can cause glucosuria includehormonal disorders ,medication

Glucose(


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Protein

The glomeruli normally filter 7-10 g of protein/day, butalmost all is reabsorbed by endocytosis and subsequent

catabolized in proximal tubules.The protein test pad measures the amount ofalbumin

in the urine. Normally, there will not be detectablequantities.

When urine protein is elevated (proteinuria) ;this canbe an early sign ofkidney disease .Albumin is smallerthan most other proteins (68 kDa)and is typically thefirst protein that is seen in the urine when kidney

dysfunction begins to develop.Other proteins are not detected by the test pad but may

be measured with a separateurine protein test .


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Ketones Ketones are not normally found in the urine.

Ketones can be extra-synthesized in cases ofstarvation / Diabetic keto-acidosis (DKA.

Ketones in urine can give an early indication ofinsufficient insulin in a person who has diabetes

(Ketosis). Other conditions that may cause ketonuria: Severe

exercise, loss of carbohydrates, such as withfrequent vomiting, can also increase fat metabolism,

resulting in ketonuria.

Bili bi


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Bilirubin

Bilirubin is not present in the urine of normal healthy individuals.Bilirubin is a waste product that is produced by the liver from thehemoglobin of RBCs that are removed from circulation. It becomes acomponent of bile, a fluid that is secreted into the intestines to aid in

food digestion. In certainliver diseases ,such as biliary obstruction orhepatitis ,

bilirubin leaks back into the blood stream and is excreted in urine. Thepresence of bilirubin in urine is an early indicator of liver disease andcan occur before clinical symptoms such asjaundicedevelop.

Urobilinogen Urobilinogen is normally present in urine in low concentrations. It is

formed in the intestine from bilirubin, and a portion of it is absorbedback into the bloodstream.

Positive test results help detect liver diseases such as hepatitis andcirrhosisand conditions associated with increased RBC destruction(hemolytic anemia)

When urine urobilinogen is low or absent in a patient with urinebilirubin and/or signs of liver dysfunction, it can indicate the presenceof hepatic or biliary obstruction

Leukocyte Esterase


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Leukocyte Esterase Leukocyte esterase is anenzymepresent in most white blood cells

(WBCs).

Normally, a few white blood cells are present in urine and this testis negative. When the number of WBCs in urine increases

significantly, this screening test will become positive. When the WBC count in urine is high, it means that there is

inflammation in the urinary tract or kidneys. The most commoncause for WBCs in urine (leukocyturia) is a bacterial urinary tractinfection (UTI ), such as a bladder or kidney infection.

Nitrite This test detects nitrite and is based upon the fact that many

bacteria can convert nitrate to nitrite in urine.

Normally the urinary tract and urine are free of bacteria. When

bacteria find their way into the urinary tract, they can cause aurinary tract infection (UTI). A positive nitrite test result can indicatea UTI.

However, since not all bacteria are capable of converting nitrate tonitrite, you can still have a UTI despite a negative nitrite test.


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URINE collection

Urine for a urinalysis can be collected at any time but the firstmorning sample is considered the most valuable because it ismore concentrated and more likely to yield abnormalities ifpresent.

It is important to clean the genitalia before collecting urine .Bacteriaand cells from the surrounding skin can contaminatethe sample and interfere with the interpretation of test results.

Menstrual blood and vaginal secretions can also be a source ofcontamination.

As start to urinate, let some urine fall into the toilet, then

collect one to two ounces of urine in the container provided,then void the rest into the toilet. This type of collection is calleda midstreamcollection or a clean catch .

Another samples, random, night, P.P, 24-hours may be used.

The urine sample should be refrigerated if the analysis delays

or a preservative may be added (azide, HCl, Pr-inh.).


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BUN ( urea ) BUN results from catabolism of amino acids.

After filtration, about 50% is reabsorbed by the tubules.

Blood level is related to: renal function, Protein intake, and liverfunction

Urea production is increased by a high protein intake , GIT

bleeding , Catabolic state and it is decreased in patients with alow protein intake or in patients with liver disease.

Less useful than Creatinine better to be used with Cr

Sensitive but non-specific test

Reference Range of Serum or plasma BUN is: 820 mg/dL. Reference Range of Blood urea = ( BUN X 2.14 ) is:

1545 mg/dL.


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Creatinine

Creatinine (Mol. Wt. 113) is formed from breaking of 1-2% daily of

muscle creatine (relative to muscle mass). Freely filtered by the glomeruli.

Not reabsorbed.

Conc inversely related to eGFR.

Low serum and urine creatinnie is found in children, females,

and elderly.

Small changes in creatinine within and around the reference

limits = large changes in GFR.

Increased conc occurred very late ( after GFR decrease about

50% of its normal value). Normal values: (Female 0.6-1.1 mg/dl) (Male 0.9-1.3 mg/dl)

BUN/Creatinine ratio 10:1


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Glomerular Filtration Rate(GFR)

Estimation of GFR is the Best single measure ofassessment of renal function since its value isproportional to the number of intact nephrons.

The GFR is the volume of fluid filtered from theglomeruli into Bowman's space per unit time.

eGFR is more accurate than serum creatinine alone.Serum creatinine is affected by muscle mass, andrelated factors of age, sex, and race.

Many methods are used to estimate the eGFR.


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Determination of Clearance Rate

Clearance = (U xV)/PU is the urinary concentration of creatinine (mg/dl)

V is the 24-hours collected urine (L).

P is the plasma concentration of creatinine (mg/dl)

Units = volume/unit time (mL/min)

Normal: Male: 97 to 137 ml/min.

Female: 88 to 128 ml/min.

abeer renal function testsamr renal function tests renal block

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