KIDNEY FUNCTION TEST AND NON-PROTEIN NITROGENS

Kidney

• paired bean shaped organ, located retriperitoneally either of the spinal column

• Functional Unit: Nephron

Glomerulus

• non selective filter of plasma substances

• The main filtering unit of the kidneys

• Act as sieve of the kidneys

Proximal Convoluted Tubule

Immediate reabsorption of essential substances (e.g glucose, water, peptides and also the other nutrients from the tubule fluid back into the blood)

Loop of Henle

• Site of the renal concentration

• Water and Sodium Chloride is also reabsorbed from the filtrate

Distal Convoluted Tubule

Final site for the adjustment of the urine composition

Collecting Duct

• Final site for the renal concentration, wherein it will collect the urine and later on it will transport it to pelvis to the ureters. And temporary stored in urinary bladder

• There is still reabsorption of excess water

CLEARANCE TEST

• Tests which measure the rate of glomerular filtration

• Usually the unit is mL/min

• Cleared or removed the substances from the plasma to urine

CREATININE CLEARANCE TEST

• Creatinine occurring through metabolic production is eliminated from the plasma by glomerular filtration and therefore a measurement of its rate of clearance affords a measure of the process

• Excellent measure of renal function

• It is freely filtered by the glomeruli but not reabsorbed

• Daily the creatinine excreted is 1.2 to 1.5g per day

INCREASED CREATININE CLEARANCE

• Increased in URINE

• Decreased in the PLASMA

• High cardiac output

• Pregnancy

• Burns

• Carbon Monoxide Poisoning

DECREASED CLEARANCE TEST

• Decreased in URINE

• Increased PLASMA

• Impaired kidney function

• Shock, Dehydration

• . Hemorrhage

• Congestive heart failure

INULIN CLEARANCE TESTS

• freely passes the glomeruli but is neither secreted nor absorbed by the tubules

• Considered to be the most accurate measure of GFR

• This is the reference method

• Not commonly/routinely used

• Good Measure for Clearance

• Not excreted and not reabsorbed

UREA CLEARANCE TEST

• Urea is freely filtered by the glomeruli but variably reabsorbed in the tubules depending upon the transit time (rate of urine flow along the course of tubules) of urea filtrate

CYSTATIN C

• Produced at a constant rate by all nucleated cells

• Not secreted but completely reabsorbed

Serum Cystatin C Levels- Increases more rapidly than creatinine in the early stages of GFR involvement

B2-MICROGLOBULIN

• Easily filtered and reabsorbed

• Usually elevated in cases of there is increased cellular turnover

• Increased in inflammation and in renal failure

MYOGLOBIN

• Associated with acute skeletal and cardiac muscle injury

• Rhabdomyolysis → acute renal failure

• Continuous breaking down of muscles

• Myo = muscles (associated with muscle injuries)

• Myoglobin released from the skeletal muscle is enough to overload the PCT and later on cause acute renal failure

MICROALBUMINURIA

• Small amount of albumin in the urine

• Trace amount of albumin in the urine

• Can lead to kidney damage

EXCRETORY TEST

Both utilizes dye

PARA-AMINO HIPPURATE TEST (PAH) OR DIODRAST TEST

• Measures the renal plasma flow

• REFERENCE RANGE: 600 to 700 mL/min

PHENOLSULFONAPHTHALEIN (PSP) DYE EXCRETION TEST

• Dye excreted will be proportional or equal to tubular mass

• REFERENCE RANGE: 1200 mL/min

CONCENTRATION TEST

• Reflect the function of collecting tubules and Loop of Henle

• More on assessing the quantity of solutes in urine

• Assess the ability of those parts to produce a concentrated urine

• Prevalent solute are the urea, chloride, sodium

• Preferred Sample: First Morning Urine Sample

SPECIFIC GRAVITY

• Measurement is affected by the solute number and mass

• The simplest

• REFERENCE RANGE: 1.005 to 1.030

OSMOLALITY

• Only affected by the number of solute present

• Serum osmolality (Due to Sodium and Chloride)

• Urine osmolality (Due to Urea)

• Useful for assessing water deficit or excess

• REFERENCE RANGES (Serum): 275 to 295 mOsm/kg

• REFERENCE RANGES (Urine): 300 to 900 mOsm/kg

DIRECT METHODS

Freezing Point Osmometry

• More on common

• Procedure using super cooling temperature (-70oC)

• Quality check the solution/freezing point osmometer you can use Sodium Chloride (QC reference solution)

• Vapor Pressure

INDIRECT METHODS

Osmolal Gap

• Difference between the measured and calculated plasma osmolality

• A sensitive indicator of alcohol and drug overdose

• Utilizes a computation

• Subtract the measured and calculated by the machine

NON-PROTEIN NITROGEN (NPN

• Test for measuring renal blood flow

• NPNs are the waste products of the body as a result of degradation (amino acids, proteins, or muscle metabolism)

UREA

• Major excretory product of protein metabolism

• Formed in the liver from amino groups (NH2) and free ammonia generated during protein catabolism

• Check/Verify the adequacy of dialysis

• Protein Content of the Diet

• Rate of Protein Catabolism

• 90% Excreted, 10% Remains in the bloodstream

BLOOD UREA NITROGEN (BUN)

• In severe liver damage = Decreased Levels of Urea

• It is also the first metabolite to increase in KIDNEY DAMAGE or DISEASES

• It is used as a SCREENING TEST for kidney disease

• Urea is readily removed by DIALYSIS

CHEMICAL METHODS – DIRECT METHODS

A. DIACETYL MONOXIME METHOD (DAM)

• Also known as Fearon’s Reaction

• Urea + Dam → yellow diazine derivative

• Arsenic thiosemicarbazide is added to enhance color reaction and has the ability to exclude protein interferences

ENZYMATIC METHOD – INDIRECT METHOD

• Indirect – have to generate a compound first or a different reaction

• PRIMARY STEP – hydrolysis of urea by urease

A. UREASE-NESSLER METHOD

• Urea + Urease → NH3 + CO2

• NH3 + Nessler’s reagent → Dimercuric Ammonium Iodide (yellow)

• Ammonia will continue on the reaction

B. UREASE BERTHELOT METHOD

• Urea + Urease → NH3 + CO2

• NH3 + phenol hypochlorite → indophenol (blue)

• Phenol hypochlorite is phenol + sodium chlorite

C. COUPLED UREASE/ GLUTAMATE DEHYDROGENASE (GLD)

• Method – UV Enzymatic Method

• In lab, we usually use reagents either GLD or Berthelot . If we use UV enzymatic method, colorless solution.

D. INDICATOR DYE

E. CONDUCTIMETRIC

• Conversion of unionized urea to NH4 and CO3

• Results in increased conductivity (Electrode)

ISOTOPE DILUTION MASS SPECTROPHOTOMETRY

• REFERENCE METHOD

• Expensive so not recommended for routine purposes

• REFERENCE VALUE: 8-23 mg/dL (2.9 – 8.2 mmol/L)

• CONVERSION FACTOR: 0.357

UREMIA

defined as the increased in urea and creatinine (azotemia) with accompanying clinical signs and symptoms of renal failure like

METABOLIC ACIDOSIS

Acidic environment in the body because we cannot excrete acidic products in the body. It only retains in the bloodstream

HYPERKALEMIA

• Increased potassium. We cant excrete potassium, it increases in the blood.

EDEMA

• One of general function of kidney is to regulate water volume balance, if we cant reabsorb and excrete water properly. Water will retain in the body, there will be generalized edema

• If px have kidney problem, manas si patient

AZOTEMIA CAN BE DIFFERENTIATED INTO THREE

Pre-Renal

circulation through kidneys is less efficient than usual

AZOTEMIA CAN BE DIFFERENTIATED INTO THREE

Renal

characterized by lesions on the parenchyma (tubular injury)

AZOTEMIA CAN BE DIFFERENTIATED INTO THREE

Post-Renal

obstruction in the urinary tract

CREATININE

• Creatinine is the principal waste product of muscular metabolism derived mainly from creatine (alpha-methyl guanidoacetic acid)

• Directly proportional to muscle mass

• Compared to urea, this is not easily removed by dialysis

DIRECT JAFFE METHOD

• Formation of red tautometer of creatinine picrate when creatinine serum is made to react with a freshly prepared alkaline sodium picrate solution

• Product is red or red-orange. Dependent on concentration, higher concentration yields darker product

FOLIN WU METHOD

Sensitive but not specific

LLOYD OR FULLER’S EARTH METHOD

• Both sensitive and specific

• Lloyd’s reagent = Sodium aluminum silicate

• Fuller’s reagent = Aluminum magnesium silicate

• Not routinely used because it is time-consuming and not readily automated

DIRECT REDOX METHODS

• Uric acid is oxidized to allantoin and CO2 by phosphotungstic acid reagent

• In the process, phosphotungstic acid is reduced to tungsten blue under alkaline condition

KINETIC JAFFE METHOD

• Requires equipment for precision

• Serum is mixed with alkaline picrate solution and the rate of change in absorbance is measured between 2 points

CARAWAY METHOD

• Oldest method of uric acid determination

MODIFICATION OF CARAWAY

Henry’s Method

ENZYMATIC METHOD – INDIRECT METHOD

BLAUNCH AND KOCK (URICASE METHOD)

Differential or Absorption Spectrophotometry

BERTHELOT'S REACTION

The ammonia formed reacts with phenol and alkaline hypochlorite using sodium nitroprusside as catalyst to form indophenol blue

NESSLERIZATION

• yellow in color nitrogen is present in low to moderate concentration

• orange brown - nitrogen is present in high concentration