Organ function test

Liver function test

Major functions of liver

• 1. Metabolic functions : Liver actively participates in carbohydrate, lipid, protein, mineral and vitamin metabolisms.
• 2. Excretory functions : Bile pigments, bile salts and cholesterol are excreted in the bile into intestine.
• 3. Protective functions and detoxification : Kupffer cells of liver perform phagocytosis to eliminate foreign compounds. Ammonia is detoxified to urea. Liver is responsible for the metabolism of xenobiotics (detoxification).
• 4. Hematological functions : Liver participates in the formation of blood (particularly in the embryo), synthesis of plasma proteins (including blood clotting factors) and destruction of erythrocytes.
• 5. Storage functions : Glycogen, vitamins A, D and B12 and trace element iron are stored in liver.

Metabolism of bilirubin

• i. The end-products of heme catabolism are bile pigments . Bilirubin has no function in the body and is excreted through bile.
• ii. From hemoglobin, the globin chains are separated, they are hydrolyzed and the amino acids are channeled into the body amino acid pool. The iron liberated from heme is re-utilized.
• iii. The porphyrin ring is broken down in reticuloendothelial (RE) cells of liver, spleen and bone marrow to bile pigments, mainly bilirubin.
• iv. About 6 g of Hb is broken down per day, from which about 250 mg of bilirubin is formed. From myoglobin and other heme containing proteins, another 50 mg of bilirubin is formed. Approximately 35 mg of bilirubin is formed from 1 g of Hb. A total of 300 mg of bilirubin is formed every day; of which 80% is from destruction of old RBCs, 10% from ineffective erythropoiesis and the rest 10% from degradation of myoglobin and other heme containing proteins.

• v. Microsomal heme oxygenase system: Heme is degraded primarily by a microsomal enzyme system; heme oxygenase. It requires molecular oxygen and NADPH; for the regeneration of NADPH cytochrome c is required. The enzyme is induced by heme. The oxygenase enzyme specifically catalyzes the cleavage of the alpha methenyl bridge, which is linking the pyrrole rings I and II. The alpha methenyl bridge is quantitatively liberated as carbon monoxide.
• vi. The Fe++ liberated is oxidized to Fe+++ and taken up by transferrin.
• vii. The linear tetrapyrrole formed is biliverdin which is green in color. In mammals it is further reduced to bilirubin, a red-yellow pigment, by an NADPH dependent biliverdin reductase . But birds, amphibians and rabbits excrete the green biliverdin itself

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• i. The liver plays the central role in the further disposal of the bilirubin. The bilirubin formed in the reticuloendothelial cells is insoluble in water. The lipophilic bilirubin is therefore transported in plasma bound to albumin.
• ii. One molecule of albumin can bind 2 molecules of bilirubin. 100 mL of plasma can transport up to 25 mg of bilirubin.
• iii. Albumin binds bilirubin in loose combination. So when present in excess, bilirubin can easily dissociate from albumin. The binding sites for bilirubin on albumin can be occupied by aspirin, penicillin, etc. Such drugs can, therefore, displace bilirubin from albumin. Hence, care should be taken while administering such drugs to newborn babies to avoid kernicterus.
• iv. When the albumin-bilirubin complex reaches the sinusoidal surface of the liver, the bilirubin is taken up. The uptake is a carrier mediated active process.

Conjugation in Liver

• i. Inside the liver cell, the bilirubin is conjugated with glucuronic acid, to make it water-soluble. The first carbon of glucuronic acid is combined with the carboxyl group of the propionic acid side chains of the bilirubin molecule. About 80% molecules are in the diglucuronide form, while 20% are monoglucuronides.
• ii. Drugs like primaquine, novobiocin, chloramphenicol, androgens and pregnanediol may interfere in this conjugation process and may cause jaundice.
• Excretion of Bilirubin to Bile The water-soluble conjugated bilirubin is excreted into the bile by an active process and this occurs against a concentration gradient.
• This is the rate-limiting step in the catabolism of heme. It is induced by phenobarbitone.
• Excretion of conjugated bilirubin into bile is mediated by an ATP binding cassette protein which is called Multispecific organic anion transporter (MOAT), located in the plasma membrane of the biliary canaliculi. This protein is very similar to the Multidrug resistance protein (MRP-2).

Fate of Conjugated Bilirubin in Intestine

• i. The conjugated bilirubin reaches the intestine through the bile. Intestinal bacteria deconjugate the conjugated bilirubin.
• ii. This free bilirubin (36 hydrogen atoms) is further reduced to a colorless tetrapyrrole urobilinogen (UBG) (44 hydrogen)
• iii. Further reduction of the vinyl substituent groups of UBG leads to formation of mesobilinogen and stercobilinogen (SBG) (48 hydrogen). The SBG is mostly excreted through feces (250–300 mg/day).
• Enterohepatic Circulation
• About 20% of the UBG is reabsorbed from the intestine and returned to the liver by portal blood. The UBG is again re-excreted (enterohepatic circulation)
• Since the UBG is passed through blood, a small fraction is excreted in urine (less than 4 mg/day).

Final Excretion

• i. UBG and SBG are both colorless compounds but are oxidized to colored products, urobilin (42 hydrogen) or stercobilin (46 hydrogen) respectively by atmospheric oxidation.
• ii. Both urobilin and stercobilin are present in urine as well as in feces. The normal color of feces is due to these compounds.
• iii. Black color is seen in constipation. If intestinal flora is decreased by prolonged administration of antibiotics, bilirubin is not reduced to bilinogens, and in the large gut, it is re-oxidized by O2 to form biliverdin. Then green tinged feces is seen, especially in children.
• Plasma Bilirubin
• i. Normal plasma bilirubin level ranges from 0.2–1mg/ dL. The unconjugated bilirubin is about 0.2–0.6 mg/dL, while conjugated bilirubin is only 0.2–0.4mg/dL.
• ii. If the plasma bilirubin level exceeds 1 mg/dL, the condition is called hyperbilirubinemia. Levels between 1 and 2 mg/dL are indicative of latent jaundice.
• iii. When the bilirubin level exceeds 2 mg/dL, it diffuses into tissues producing yellowish discoloration of sclera, conjunctiva, skin and mucous membrane resulting in jaundice. Icterus is the Greek term for jaundice.
• Jaundice is derived from latin i.e. jaune – yellow.

Classification of jaundice

• Jaundice (also known as icterus) may be more appropriately considered as a symptom rather than a disease. It is rather difficult to classify jaundice, since it is frequently caused due to multiple factors. For the sake of convenience to understand, jaundice is classified into three major types—hemolytic, hepatic and obstructive.
• 1. Hemolytic jaundice : This condition is associated with increased hemolysis of erythrocytes (e.g. incompatible blood transfusion, malaria, sickle cell anemia).
• This results in the overproduction of bilirubin beyond the ability of the liver to conjugate and excrete the same.
• It should, however be noted that liver possesses a large capacity to conjugate about 3.0 g of bilirubin per day against the normal bilirubin production of 0.3 g/day.
• In hemolytic jaundice, more bilirubin is excreted into the bile leading to the increased formation of urobilinogen and stercobilinogen. Hemolytic jaundice is characterized by
• Elevation in the serum unconjugated bilirubin.
• Increased excretion of urobilinogen in urine
• Dark brown colour of feces due to high content of stercobilinogen

2. Hepatic (hepatocellular) jaundice :

• This type of jaundice is caused by dysfunction of the liver due to damage to the parenchymal cells.
• This may be attributed to viral infection (viral hepatitis), poisons and toxins (chloroform, carbon tetrachloride, phosphorus etc.) cirrhosis of liver, cardiac failure etc.
• Among these, viral hepatitis is the most common. Damage to the liver adversely affects the bilirubin uptake and its conjugation by liver cells. Hepatic jaundice is characterized by
• Increased levels of conjugated and unconjugated bilirubin in the serum.
• Dark coloured urine due to the excessive excretion of bilirubin and urobilinogen.
• Increased activities of alanine transaminase (SGPT) and aspartate transaminase (SGOT) released into circulation due to damage to hepatocytes.
• The patients pass pale, clay coloured stools due to the absence of stercobilinogen.
• The affected individuals experience nausea and anorexia (loss of appetite).

3. Obstructive (regurgitation) jaundice :

• This is due to an obstruction in the bile duct that prevents the passage of bile into the intestine. The obstruction may be caused by gall stones, tumors etc. Due to the blockage in bile duct, the conjugated bilirubin from the liver enters the circulation.
• Obstructive jaundice is characterized by
• Increased concentration of conjugated bilirubin in serum.
• Serum alkaline phosphatase is elevated as it is released from the cells of the damaged bile duct.
• Dark coloured urine due to elevated excretion of bilirubin and clay coloured feces due to absence of stercobilinogen.
• Feces contain excess fat indicating impairment in fat digestion and absorption in the absence of bile (specifically bile salts).
• The patients experience nausea and gastrointestinal pain.

Jaundice due to genetic defects

• There are certain hereditary abnormalities that cause jaundice
• Neonatal-physiological jaundice Physiological jaundice is not truly a genetic defect. It is caused by increased hemolysis coupled with immature hepatic system for the uptake, conjugation and secretion of bilirubin.
• The activity of the enzyme UDP glucuronyltransferase is low in the newborn. Further, there is a limitation in the availability of the substrate UDP-glucuronic acid for conjugation.
• The net effect is that in some infants the serum uncojugated bilirubin is highly elevated (may go beyond 25mg/dl), which can cross the bloodbrain barrier.
• This results in hyperbilirubinemic toxic encephalopathy or kernicterus that causes mental retardation. The drug phenobarbital is used in the treatment of neonatal jaundice, as it can induce bilirubin metabolising enzymes in liver.
• In some neonates, blood transfusion may be necessary to prevent brain damage
• Phototherapy
• Bilirubin can absorb blue light (420–470 nm) maximally. Phototherapy deals with the exposure of the jaundiced neonates to blue light. By a process called photoisomerization, the toxic native unconjugated bilirubin gets converted into a non-toxic isomer namely lumirubin. Lumirubin can be easily excreted by the kidneys in the unconjugated form (in contrast to bilirubin which cannot be excreted). Serum bilirubin is monitored every 12–24 hours, and phototherapy is continuously carried out till the serum bilirubin becomes normal (< 1 mg/dl).

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Crigler-Najjar syndrome type i�

• This is also known as congenital nonhemolytic jaundice. It is a rare disorder and is due to a defect in the hepatic enzyme UDP glucuronyltransferase. Generally, the children die within first two years of life. Bilirubin > 20-50 mg/dl. kernicterus
• Crigler-Najjar syndrome type II
• This is again a rare hereditary disorder and is due to a less severe defect in the bilirubin conjugation. It is believed that hepatic UDPglucuronyltransferase that catalyses the addition of second glucuronyl group is defective.
• The serum bilirubin concentration is usually less than 20 mg/dl and this is less dangerous than type I.
• Gilbert's disease This is not a single disease but a combination of disorders. These include
• 1. A defect in the uptake of bilirubin by liver cells.
• 2. An impairment in conjugation due to reduced activity of UDP glucuronyltransferase.
• 3. Decreased hepatic clearance of bilirubin

van den Bergh reaction

• i. The bilirubin is estimated by van den Bergh reaction, where diazotized sulfanilic acid (sulfanilic acid in HCl and sodium nitrite) reacts with bilirubin to form a purple colored complex, azobilirubin.
• ii. Normal serum gives a positive van den Bergh reaction.
• iii. When bilirubin is conjugated, the purple color is produced immediately on mixing with the reagent, the response is said to be van den Bergh direct positive.
• iv. When the bilirubin is unconjugated, the color is obtained only when alcohol is added, and this response is known as indirect positive.
• v. If both conjugated and unconjugated bilirubin are present in increased amounts, a purple color is produced immediately and the color is intensified on adding alcohol. Then the reaction is called biphasic.
• vi. In Hemolytic jaundice, unconjugated bilirubin is increased. Hence van den Bergh test is indirect positive.
• In obstructive jaundice, conjugated bilirubin is elevated, and van den Bergh test is direct positive.
• In hepatocellular jaundice, a biphasic reaction is observed, because both conjugated and unconjugated bilirubins are increased.

van den Bergh reaction and jaundice

• This reaction is highly useful in understanding the nature of jaundice. This is due to the fact that the type of jaundice is characterized by increased serum concentration of unconjugated bilirubin (hemolytic), conjugated bilirubin (obstructive) or both of them (hepatic).
• Therefore, the response of van den Bergh reaction can differentiate the jaundice as follows
• Indirect positive — Hemolytic jaundice
• Direct positive — Obstructive jaundice
• Biphasic — Hepatic jaundice.
• Bilirubin in urine The conjugated bilirubin, being water soluble, is excreted in urine. This is in contrast to unconjugated bilirubin which is not excreted. Bilirubin in urine can be detected by Fouchet's test or Gmelin's test

ALANINE AMINO TRANSFERASE (ALT)

• i. In old literature, it was called as serum glutamate pyruvate transaminase (SGPT). The enzyme needs pyridoxal phosphate as co-enzyme.
• ii. Normal serum level of ALT for male is 13–35 U/L and for female is 10–30 U/L. Very high values (300 to 1000 U/L) are seen in acute hepatitis, either toxic or viral in origin (infective hepatitis).
• iii. Both ALT and AST levels are increased in liver disease, but ALT > AST. Rise in ALT levels may be noticed several days before clinical signs such as jaundice are manifested.
• iv. Moderate elevation of amino transferases often between 100–300 U/L is seen in alcoholic hepatitis, autoimmune hepatitis, Wilson’s disease and non- alcoholic chronic hepatitis .
• v. Minor elevation less than 100U/L is seen in chronic viral hepatitis (hepatitis C), fatty liver and in non- alcoholic steatohepatitis (NASH). In chronic hepatitis and cirrhosis of liver, serum ALT poorly correlates with the degree of liver cell damage.
• vii. A normal value need not rule out minor liver diseases. On the other hand, normal persons may have elevated ALT levels. This is seen especially in obese persons. 1% loss of weight will reduce ALT values by 8%.
• Vii The degree of elevation may reflect the extent of hepatocellular necrosis. In most cases the lowering of the level of transaminases indicates recovery, but a sudden fall from a very high level may indicate poor prognosis.
• viii. Elevation of ALT is more in cases of hepatic disease compared to AST. But AST may be more than ALT in alcoholic liver disease. In alcoholic liver disease, the actual values show only mild elevation; but a ratio of AST/ALT more than two is quite suggestive.

ASPARTATE AMINO TRANSFERASE (AST)

• i. In old literature, it was called as serum glutamate oxaloacetate transaminase (SGOT). AST needs pyridoxal phosphate (vitamin B6 ) as co-enzyme.
• ii. Normal serum level of AST is 8–20 U/L. The level is elevated in myocardial infarction.
• iii. It is signifcantly elevated in liver diseases. A marked increase in AST may be seen in primary hepatomas.
• iv. In alcoholic hepatitis AST may be higher than ALT since mitochondrial enzyme is also liberated.

ALKALINE PHOSPHATASE (ALP)

• i. ALP is a nonspecific enzyme which hydrolyzes aliphatic, aromatic or heterocyclic compounds. The pH optimum for the enzyme reaction is between 9 and 10. It is activated by magnesium and manganese. Zinc is a constituent ion of ALP.
• ii. It is produced by osteoblasts of bone, and is associated with the calcification process. It is localized in cell membranes (ecto-enzyme), and is associated with transport mechanisms in liver, kidney and intestinal mucosa.
• iii. Normal serum value of ALP is 40–125 U/L. In children, the upper level of normal value may be more, because of the increased osteoblastic activity in children.
• iv. Moderate (2–3 times) increase in ALP level is seen in hepatic diseases such as infective hepatitis, alcoholic hepatitis or hepatocellular carcinoma.
• v. Very high levels of ALP (10–12 times of upper limit) may be noticed in extrahepatic obstruction (obstructive jaundice) caused by gallstones or by pressure on bile duct by carcinoma of head of pancreas. Intrahepatic cholestasis may be caused by viral hepatitis or by drugs (chlorpromazine). ALP is produced by epithelial cells of biliary canaliculi and obstruction of biliary passage with consequent irritation of epithelial cells leads to secretion of ALP into serum.
• vi. Drastically high levels of ALP (10–25 times of upper limit) are also seen in bone diseases where osteoblastic activity is enhanced such as Paget's disease (osteitis deformans), rickets, osteomalacia, osteoblastoma, metastatic carcinoma of bone and hyperparathyroidism
• .vii. There are 6 iso-enzymes for ALP. The one, which is inhibited by phenylalanine is of placental origin. It is found in blood in normal pregnancy. An iso enzyme closely resembling the placental form is characteristically seen in circulation in about 15% cases of carcinoma of lung, liver and gut and named as Regan iso-enzyme or carcinoplacental iso-enzyme

Gamma Glutamyl Transferase (GGT)

• 1. The old name was gamma glutamyl transpeptidase. It can transfer gamma glutamyl residues to substrate. In the body it is used in the synthesis of glutathione. GGT has 11 iso-enzymes. It is seen in liver, kidney, pancreas, intestinal cells and prostate gland.
• 2. Normal serum value of GGT is 10 –30 U/L. It is moderately increased in infective hepatitis and prostate cancers.
• 3. GGT is clinically important because of its sensitivity to detect alcohol abuse. GGT is increased in alcoholics even when other liver function tests are within normal limits.
• GGT level is rapidly decreased within a few days when the person stops to take alcohol. Increase in GGT level is generally proportional to the amount of alcohol intake.

Sorbitol dehydrogenase (SDH)

• Sorbitol dehydrogenase (SDH) is a liver-specific enzyme in animals, particularly used in veterinary LFTs (especially in horses and cattle) to detect acute liver damage.
• ↑ SDH = Acute hepatocellular injury (e.g., due to toxins, infection, hypoxia)
• Normal SDH = No significant hepatocyte damage or recovery phase Increased SDH activity in serum indicates:
• Acute hepatocellular (liver cell) damage
• Toxic liver injury
• Hypoxic liver damage
• Infectious hepatitis
• Normal levei 0-8 U/L

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Kidney (renal) function tests

• The kidneys are the vital organs of the body, performing the following major functions.
• 1. Maintenance of homeostasis : The kidneys are largely responsible for the regulation of water, electrolyte and acid-base balance in the body.
• 2. Excretion of metabolic waste products : The end products of protein and nucleic acid metabolism are eliminated from the body. These include urea, creatinine, creatine, uric acid, sulfate and phosphate.
• 3. Retention of substances vital to body : The kidneys reabsorb and retain several substances of biochemical importance in the body e.g. glucose, amino acids etc
• 4. Hormonal functions : The kidneys also function as endocrine organs by producing hormones.
• • Erythropoietin, a peptide hormone, stimulates hemoglobin synthesis and formation of erythrocytes.
• • 1,25-Dihydroxycholecalciferol (calcitriol) – the biochemically active form of vitamin D – is finally produced in the kidney. It regulates calcium absorption from the gut.
• • Renin, a proteolytic enzyme liberated by kidney, stimulates the formation of angiotensin II which, in turn, leads to aldosterone production. Angiotensin II and aldosterone are the hormones involved in the regulation of electrolyte balance.

Glomerular Function

• When the blood is perfused through the Bowman’s capsule, an ultrafiltrate of the blood is produced in glomerulus, while the cells and proteins are retained in the blood.
• The sieves of the glomeruli are such that hemoglobin (mol wt 67,000 D) is passed through to be excreted in urine, while albumin (mol wt 69,000 D) is retained in the blood.
• Glomerular Filtration Rate (GFR)
• i. GFR is decreased when BP is below 80 mm of mercury. The GFR is reduced when there is obstruction to the renal flow (calculi, enlarged prostate, etc.). It also decreases with age.
• ii. The renal blood flow is about 700 mL of plasma or 1200 mL of blood per minute.
• iii. The glomerular filtration rate (GFR) is 120–125 mL per minute in a person with 70 kg body weight.
• iv. Glomerular filtrate formed is about 170 to 180 liters per day, out of which only 1.5 liters are excreted as urine. This means that most of the water content of glomerular filtrate is reabsorbed.

Functions of the Tubules

• i. When the glomerular filtrate is formed, it contains almost all the crystalloids of plasma. In the proximal convoluted tubules, about 70% water, Na+ and Cl– as well as 100% glucose, amino acids and K+ are reabsorbed.
• ii. Urea, phosphate and calcium are partially absorbed.
• iii. The major processes occurring in renal tubules are the reabsorption or secretion of solutes and reabsorption of water.
• Renal Threshold and Tubular Maximum
• i. Compounds whose excretion in urine are dependent on blood level are known as threshold substances. At normal or low plasma levels, they are completely reabsorbed and are not excreted in urine. But when the blood level is elevated, the tubular reabsorptive capacity is saturated, so that the excess will be excreted in urine
• . ii. The renal threshold of a substance is the plasma level above which the compound is excreted in urine.
• iii. The maximum reabsorptive capacity of the substances is known as the tubular maximum or Tm.
• iv. For glucose, the renal threshold is 180 mg/dL and Tm is 375 mg/ min. In other words, glucose starts to appear in urine when blood level is more than 180 mg/dL, and all the glucose molecules above 375 mg are excreted in the urine.
• v. In abnormal conditions, the renal threshold may be lowered so that even at lower blood levels, compounds are excreted in urine, e.g. renal glycosuria (glucose); and renal tubular acidosis (bicarbonate).

Tests to assess renal function

• Several tests are employed in the laboratory to assess kidney (renal) function. It must, however, be remembered that about two thirds of the renal tissue must be functionally damaged to show any abnormality by these tests. The kidney function tests may be divided into four groups.
• 1. Glomerular function tests : All the clearance tests (inulin, creatinine, urea) are included in this group.
• 2. Tubular function tests : Urine concentration or dilution test, urine acidfication test.
• 3. Analysis of blood/serum : Estimation of blood urea, serum creatinine, protein and electrolyte are often useful to assess renal function.
• 4. Urine examination : Simple routine examination of urine for volume, pH, specific gravity, osmolality and presence of certain abnormal constituents (proteins, blood, ketone bodies, glucose etc.) also helps, of course to a limited degree, to assess kidney functioning.

MARKERS OF GLOMERULAR FILTRATION RATE

• Clearance Tests
• Measurement of the clearance is predominantly a test of glomerular filtration rate (GFR).
• Measurement of glomerular filtration rate (GFR) provides the most useful general index for the assessment of the severity of renal damage.
• A decrease in the renal function is due to the loss of functional nephrons, rather than a decrease in the function of individual nephron.
• Clearance is defined as the volume of blood or plasma completely cleared of a substance per unit time. ii. It is expressed as milliliter of plasma per minute (not as g or mg).

• It is calculated by using the formula: C=U × V /P where
• U = concentration of the substance in urine;
• P = concentration of the substance in plasma or serum and
• V = the mL of urine excreted per minute. The value is expressed as mL/minute.
• If the substance is freely filtered across the capillary wall, and neither secreted nor reabsorbed, then its clearance is equal to glomerular filtration rate.
• Exogenous markers are inulin, 51Cr-labeled EDTA, 99Tec-labeled EDTA, etc. These are not used in clinical practice, since it involves administration of extraneous compounds.
• Endogenous markers are urea and creatinine. None of these markers are ideal, but creatinine is the best out of all of them.

Creatinine Clearance Test

• i. Creatinine is a waste product, formed from creatine phosphate. This conversion is spontaneous, non-enzymatic, and is dependent on total muscle mass of the body. It is not affected by diet, age or exercise. Women and children excrete less creatinine than men, because of their smaller muscle mass. About 98% of creatine pool is in muscle. About 1.6% is converted to creatinine per day, which is rapidly excreted.
• ii. Since the production is continuous, the blood level will not fluctuate much, making creatinine an ideal substance for clearance test.
• iii. In traditional method the 24 hours urine sample was collectediv. In order to circumvent the difficulty of urine collection, nowadays the procedure is modified to collect urine for 1 hr, after giving water.

• Adult males, 0.7 – 1.4 mg/dL Adult females, 0.6 – 1.3 mg/dL Children, 0.4 – 1.2 mg/dL.
• Creatinine level more than 1.5 mg/dL indicates impairment of renal function.
• A decreased creatinine clearance is a very sensitive indicator of reduced glomerular filtration rate. The value of creatinine clearance is close to GFR, hence its measurement is a sensitive and good approach to assess the renal glomerular function.
• Creatinine clearance may be defined as the volume (ml) of plasma that would be completely cleared of creatinine per minute.
• C=U x V/P
• where U = Urine concentration of creatinine
• V = Urine output in ml/min (24 hr urine volume divided by 24 × 60)
• P = Plasma concentration of creatinine. As already stated, creatinine concentration in urine and plasma should be expressed in the same units (mg/dl or mmol/l).
• The normal range of creatinine clearance is around 120–145 ml/min.
• Clearance value up to 75% of the average normal value may indicate adequate renal function. In older people, the clearance is decreased.
• A decrease in creatinine clearance value (< 75% normal) serves as sensitive indicator of a decreased GFR, due to renal damage. This test is useful for an early detection of impairment in kidney function, often before the clinical manifestations are seen

Procedure for Creatinine Clearance Test

• Creatinine is quantitated by Jaffe’s test (alkaline picrate). Test kit based on specific enzymatic reaction is also available
• Give 500 mL of water to the patient, to promote good urine flow.
• After about 30 minutes, ask to empty the bladder and discard the urine. Exactly after 60 minutes, again void the bladder and collect the urine, and note the volume. Take one blood sample. Creatinine level in blood and urine are tested and calculated as
• C = U X V/ P
• where U = Urine concentration of creatinine
• V = Urine output in ml/min (24 hr urine volume divided by 24 × 60)
• P = Plasma concentration of creatinine.

Urea clearance test

• Urea is the end product of protein metabolism. After being filtered by the glomeruli, it is partially reabsorbed by the renal tubules.
• Hence, urea clearance is less than the GFR and, further, it is influenced by the protein content of the diet. For these reasons, urea clearance is not as sensitive as creatinine clearance for assessing renal function. Despite this fact, several laboratories traditionally use this test.
• Urea clearance is defined as the volume (ml) of plasma that would be completely cleared of urea per minute.
• It is calculated by the formula Cm = UX V/P
• where Cm = Maximum urea clearance
• U = Urea concentration in urine (mg/ml)
• V = Urine excreted per minute in ml
• P = Urea concentration in plasma (mg/ml). The above calculation is applicable if the output of urine is more than 2 ml per minute. This is referred to as maximum urea clearance and the normal value is around 75 ml/min.

• Standard urea clearance It is observed that the urea clearance drastically changes when the volume of urine is less than 2 ml/min. This is known as standard urea clearance (Cs ) and the normal value is around 54 ml/min. It is calculated by a modified formula
• Cs = U x V/ P
• Diagnostic importance
• A urea clearance value below 75% of the normal is viewed seriously, since it is an indicator of renal damage. Blood urea level as such is found to increase only when the clearance falls below 50% normal. As already stated, creatinine clearance is a better indicator of renal function.

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Cardiac function test

• Cardiac enzymes and Biomarkers used mainly in myocardial infraction

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Pancreatic Function Tests

• The exocrine pancreas secretes about 1000–2500 mL of juice in 24 hours. The fluid is alkaline and contains bicarbonate and enzymes. This secretion is under the control of the hormones, Secretin and Cholecystokinin.
• Secretin is produced under the stimulation of gastric HCl. Secretin produces a secretion with high bicarbonate content.
• Gastrin stimulates production of cholecystokinin (CCK), which in turn produces pancreatic secretion rich in enzymes.
• The major enzymes present in pancreatic juice are amylase, lipase and proteolytic enzymes (trypsin, chymotrypsin, carboxypeptidase, elastase) as their zymogens.

Paccrease function test

• pancreatitis
• It is an inflammation of the pancreas, causing leakage of the digestive enzymes whereby the pancreas literally starts to "digest itself". Pancreatitis can be acute (sudden) or chronic (happening over a course of time). Both acute and chronic forms are serious and can be life-threatening, especially the acute form. For the majority of cases, the cause is unknown. Here are some potential risk factors:
• i. Hyperlipidemia (high fat content in blood).
• ii. Obesity, Trauma, such as a severe abdominal injury.
• iii. High fat meal (trigger for hyperlipidemia)

• Measurement of pancreatic enzymes: Amylase or alpha-1,4-glucosidase is the major enzyme which digests starch.
• The serum amylase contains the P (pancreatic) and S (salivary) iso-enzymes. These two can be distinguished by the inhibition test.
• A protein inhibitor, present in alcoholic extracts of wheat will selectively inhibit the S isoenzyme.
• Normal amylase level in serum is 50–120 units.
• The level rises within 5 hours of the onset of acute pancreatitis and the level reaches a peak within 12 hours. But the level need not parallel the severity of the disease. Within 2–4 days of the attack, the level returns to normal.
• As the serum amylase level starts falling, urinary amylase level rises. If the sample is collected too early, the serum amylase levels may not show the expected rise. If the sample is collected too late, again serum amylase may be low due to necrosis of the pancreatic tissue.

• Amylase level in blood is mildly increased in cases of cholecystitis, peptic ulcer, diseases of mesentery and obstruction of intestine.
• A small percentage of patients with acute pancreatitis fails to show any rise.
• No significant change or only mild elevation is noticed in chronic pancreatitis.

Serum lipase

• is the major lipolytic enzyme which hydrolyzes glycerol esters of long chain fatty acids.
• The level in blood is highly elevated in acute pancreatitis and this persists for 7 – 14 days. Thus lipase remains elevated longer than amylase. Moreover, lipase is not increased in salivary diseases. Therefore, lipase estimation has advantage over amylase.
• Pancreatic elastase: Another test for the diagnosis of pancreatic insufficiency is pancreatic elastase. ELISA test kits are available; a value of >200 ug in stool sample indicates normal exocrine pancreatic function and values<200ug indicates exocrine pancreatic insufficiency.