Lab Medicine Conference : Renal & Liver Function Tests Jim Holliman, M.D., F.A.C.E.P. Professor of...
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Transcript of Lab Medicine Conference : Renal & Liver Function Tests Jim Holliman, M.D., F.A.C.E.P. Professor of...
Lab Medicine Conference :
Renal & Liver FunctionTests
Jim Holliman, M.D., F.A.C.E.P.Professor of Surgery and Emergency Medicine
Director, Center for International Emergency MedicineM. S. Hershey Medicial Center
Penn State UniversityHershey, Pennsylvania, U.S.A.
Lab Medicine Conference :Renal and Liver Function Tests
Lecture Objectives–Review renal & liver physiology as it relates to clinical testing–Review methodology for RFT's & LFT's–Discuss indications for obtaining RFT's & LFT's–Determine cost-effectiveness of RFT's & LFT's
Physiology of Creatinine
Is breakdown product of creatine (the storage source for high-energy phosphate in muscle cells)
CPK acts to add high energy phosphate to creatine from ATP
Creatine-phosphate transfers the phosphate to re-make ATP when energy is needed for metabolism
Physiology of Creatinine (cont.)
Synthesis of creatine–First step (guanidoacetate) occurs in kidney, small bowel, pancreas, liver–Second step (methylation of guanidoacetate) occurs in liver
Distributed throughout body, mainly to muscle
Total body content relatively constant & proportional to muscle mass
Metabolic Breakdown of Creatine
Creatine phosphate undergoes spontaneous & irreversible breakdown to creatinine
Converted at constant rate : 2 % of total body stores per 24 hours
Muscle mass is main determinant of amount produced
Renal Handling of Creatinine
Found in all body secretions, including CSFHas no metabolic "usefulness"Excreted almost entirely via kidneysFreely filtered at glomerulusNo passive or active reabsorption along
nephronSo, major determinant of serum level is degree
of renal functionRate of urine flow has no effect on serum level
Renal handling of creatinine
Urea Physiology
Major end product of metabolism of nitrogen-containing substances (mainly protein)
Generated mainly in liver–Small amount made in brain
Freely diffusable across cell membranes except that of urinary bladder
Renal Handling of UreaExcreted mainly renally
–Small amounts lost in sweat or metabolized by gut bacteria
Freely filtered at glomerulus1/2 of filtered urea reabsorbed in proximal
tubuleWater reabsorption in distal tubule (via
ADH) & collecting ducts increases tubular luminal concentration of urea
While urea concentration in urine is high, only 40 to 80 % of filtered urea is excreted
Renal handling of urea
Urine Flow Effects on Urea Levels
Major determinant of urea reabsorption is rate of urine flow–Depends on glomerular integrity & state of hydration
At high urine flow rates (> 2 ml/min.) : 40 % of filtered urea is reabsorbed
At lower flow rates, amount of reabsorbed urea proportionately increases
Urea load filtered varies with degree of dietary protein intake & tissue breakdown
General Measurement Methodology for Creatinine &
BUNDone on serumRed top tubeShould be run in 2 to 3 hoursNo problems related to sample
collectionFree hemoglobin may interfere with
assays
Measurement of Creatinine
Jaffe reaction is standard method–Red solution results from reaction of creatinine & picric acid in alkaline medium–Color change is proportional to amount of creatinine, & follows Beer's Law–Reaction is sensitive to temp. & pH–Pre-Rx with aluminum silicate (Lloyd's Reagent) improves specificity
Sakaguchi color reaction is alternate method
Urea Analysis Quantification
Enzyme urease added to specimen–Catalyzes hydrolysis of urea to carbonic acid & ammonia–Amount of ammonia produced is directly proportional to amount of urea
Ammonia is then quantified–Automated analyzers used
ƒ React ammonia with alphaketoglutaric acidƒ Or, an ammonia - sensing electrode is used
Urea Analysis : Alternate Method
Diacetyl reaction with urea–Forms a measureable chromogen–Simple to perform–Disadvantages :
ƒ Less specificƒ The reagents stinkƒ Non-linear photometric curve
Normal Reference Rangesfor BUN & Creatinine
BUN :–8 to 26 mg/dl–2.9 to 9.3 mmol/liter (International Units)
Creatinine–0.7 to 1.5 mg/dl–0.062 to 0.113 mmol/liter
Normal BUN : Creat. ratio : –8 to 15 : 1
Azotemia
Represents abnormal condition in which the non-protein nitrogenous (NPN) compounds of urea & creatinine are elevated
Classed as :–Prerenal–Renal–Postrenal
General Causes of Hyperuremia(BUN > 26)
Prerenal azotmiaPostrenal azotemiaRenal dysfunctionIncreased protein load to liver
–Endogenous–Exogenous
Prerenal Azotemia
Functional integrity of nephrons maintained
Due to :–Inadequate renal perfusion
ƒ Dehydrationƒ Shockƒ Blood lossƒ Congestive heart failureƒ Renal artery stenosis
–Or, increased NPN production
Prerenal Azotemia :Causes of Increased NPN
ProductionEndogenous
–GI hemorrhage–Catabolic states–Antianabolic medications (steroids, tetracycline)–Cancer chemoRx
Exogenous–Increased protein intake
Causes of Postrenal AzotemiaGenerally due to urinary tract obstruction &
stasis of urine flow–Renal vein thrombosis–Bilateral ureteral stricture, calculi, or compression–Prostatic hypertrophy or tumor–Bladder obstruction
ƒ Tumorƒ Traumaƒ Stone or foreign bodyƒ Autonomic dysfunction (spinal cord dysfunction)
Causes of Renal AzotemiaDue to renal insufficiency or failure due
to intrinsic renal diseaseNot reversed by correcting pre- or post-
renal problemsEtiologies :
–Acute tubular necrosis–Acute interstitial nephritis–Nephrotic syndrome–Collagen vascular diseases–Malignancy–Metabolic diseases (esp. diabetes)
Mechanisms Causing Increased NPN
Compounds with Renal DiseaseRenal vasoconstriction / decreased
renal blood flowUrine stasis from tubular obstruction by
debrisBack leakage of filtrate into bloodDecreased glomerular permeability &
GFRShunting or redistribution of renal
blood flow resulting in decreased GFR
Causes of Hypouremia(BUN < 6 mg/dl)
Physiologic–Newborn–Pregnancy (increased GFR & urine flow)–Overhydration–Decreased protein intake
Pathologic–Acute or chronic liver disease
General Factors Affectingthe BUN Level
BUN is dependent on :–Protein intake–Functional integrity of kidneys–Functional integrity of liver–Urine flow rate
Causes of Elevated Creatinine Levels (> 1.5 mg %)
Intrinsic renal diseaseMild elevations from pre- or post- renal
azotemia(Transiently) from ingestion of large
amounts of meatExtensive muscle traumaMuscle wasting diseases (MD, ALS,
myasthenia gravis)Factitious (lab assay interference)
Causes of Factitious Elevations
of Creatinine Levels
Ketone bodiesHyperglycemiaOther proteinsBarbituratesPenicillinsCephalosporinsMethanol
Causes of Low Creatinine Levels
(< 0.7 mg %)
Basically due to decreased muscle mass :–Children–Females–Pathologic : later stages of muscle-wasting diseases
Indications to CheckBUN & Creatinine
Assess dehydration not obvious by physical exam
Differentiate renal vs. pre- or post- renal azotemia as cause for decreased urine output
Indicate presence of "occult" blood in upper GI tract
Verify renal function O.K. prior to dye studies, surgery, or nephrotoxic Rx
Evaluate for transplant rejectionMonitor for ongoing nephrotoxic drug effect
Situations NOT RequiringChecking BUN & Creatinine
Dehydration in healthy adults from gastroenteritis
Preop in healthy adults for simple abdominal or orthopedic surgery
Uncomplicated UTI'sUncomplicated respiratory tract and
head & neck infectionsMild to moderate back trauma without
hematuria
Clinical Situations Requiring Periodic
BUN & Creatinine MonitoringAminoglycosidesAmphotericinACE inhibitorsModerate to severe hypertensionDiabetesStructural renal disease (polycystic, etc.)Renal transplantRhabdomyolysis
Lab Charges at Hershey Med Center for BUN / Creatinine
Both together ("renal profile") : $11.00Either separate : $ 11.00"SMA-7" : $ 12.00Stat fee (for E.D. or inpatients) : 11/2
Times the above $
Laboratory Evaluation of Liver Disease :
Topics CoveredEnzymes
–Alkaline phosphatase–Aminotransferases (transaminases)–Lactate dehydrogenase (LDH)
Bilirubin–Direct–Indirect
Serologies for viral hepatitis
Alkaline Phosphatase (ALP) Physiology
Is heterogeneous group of enzymes catalyzing same reaction using different substrates
Hydrolyze phosphomonoesters to alcohol & inorganic phosphate at alkaline pH
Play role in transport of sugars & phosphates :–Intestinal mucosa–Renal tubules–Bone–Placenta
Isoenzymes exist but difficult to separate
Causes of Increased ALP Activity
in Serum
Physiologic–Rapid growth periods in children (ages 5 to 14 years)
ƒ Value is 2 to 3 X normal–Pregnancy–Aging–Post fatty meal
Pathologic Causes of IncreasedALP Activity in Serum
Hepatic lesions–Acute hepatitis, mononucleosis, cirrhosis, cholestasis
Osteoblastic lesions–Hyperparathyroidism, Rickets, Paget's, fractures, tumors
Tumors–Ectopic production
Gastrointestinal lesions –Stomach, duodenal, or colon ulcerations
Infarcts–Cardiac, pulmonary, renal, spleen
Physiology of Aminotransferases(Transaminases)
Catalyze reversible transfer of amino group from an alpha amino acid to an alpha keto acid
Results in formation of oxaloacetic & pyruvic acids
2 main ones in serum :–Aspartate aminotransferase (AST)
ƒ Formerly glutamate oxaloacetic transaminase (GOT)
–Alanine aminotransferase (ALT)ƒ Formerly glutamate pyruvate transaminase (GPT)
Aspartate Aminotransferase (AST)
Found in heart, liver, skeletal muscle, brain, kidney
Catalyzes transfer of amino group from aspartate to alpha ketoglutarate
Present in both mitochondria & cytosolPresent in serum as both apoenzyme &
holoenzyme (i.e., with & without cofactor pyridoxal-5-phosphate; same as for ALT)
Currently measurement of AST isoenzymes not clinically useful
Causes of Elevated AST Levels
Myocardial infarctionAcute hepatic necrosisPulmonary infarction (mild elevations in
30 %)Congestive heart failure (passive liver
congestion)PericarditisRheumatic feverSkeletal muscle injury
Alanine Aminotransferase (ALT)
Localized primarily in liverCatalyzes transfer of amino group from
alanine to alphaketoglutarateIs specific marker for hepatic disease or
injuryOnly in cytosol (not in mitochondria)
Lactate Dehydrogenase (LDH)Physiology
Catalyzes the reversible reaction :–lactate + NAD pyruvate + NADH
Maintains balance between anabolism & catabolism of carbohydrates
In liver is involved in gluconeogenesis & glycogen synthesis from lactate
In heart enables lactate to enter citric acid cycle & be used as fuel to generate ATP & NAD
Most tissues have high quantities of LDH
Isoenzymes of LDH
Are tetramers made of 4 subunits containing one of 2 tissue types : H (heart) or M (skeletal muscle)
There are 5 isozymes of LDH which consist of combos of the monomers
Normal LDH activity in serum is mainly of erythrocyte origin
Isoenzymes of LDH
TYPE MONOMERS ORGAN LOCATION
LDH 1 HHHH Myocardium, erythrocytes
LDH 2 HHHM Myocardium, erythrocytes
LDH 3 HHMM Brain, kidney, less in liver & muscle
LDH 4 HMMM Liver, brain, kidney, muscle LDH 5 MMMM Liver, muscle, less in kidney
Conditions with IncreasedLDH Levels
Cardiac–Myocardial infarction–CHF–Pulmonary infarction
Hematologic–Megaloblastic anemia–Sickle cell disease–Hemolytic anemia–Leukemias–Lymphoma–Infectious mononucleosis
Conditions with IncreasedLDH Levels (cont.)
Hepatic–Hepatitis–Obstructive jaundice–Cirrhosis–Metastatic tumors
Skeletal–Muscular dystrophy–Delerium tremens
LDH Isoenzyme Patternsin Different Conditions
DISEASE LDH-1 LDH-2 LDH-3 LDH-4 LDH-5
Acute MI + + Meg.anemia + + Hem.anemia + + Mus.dystro. + + Leukemia + + Pancreatitis + + Ca. mets + + Pulm infarct + C.H.F. + Hepatitis + Cirrhosis +
Measurement Methodologyfor Liver Enzymes
ALP–Rate of conversion of p-nitrophenylphosphate (p-NPP) to p-nitrophenol (p-NP) in presence of buffer AMP
–Change in absorbance at 405 nm due to formation of p-NP is proportional to ALP activity
AST, ALT–Change in absorbance at 340 nm due to disappearance of NADH is proportional to AST & ALT activity
LDH–Change in absorbance at 340 nm due to appearance of NADH is proportional to total LDH activity
–LDH isozymes separated electrophoretically & stained
General Diagnostic Interpretation of AST & ALT
LevelsALT is most specific measure of hepatocellular
damage (necrosis)Highest AST & ALT levels occur with :
–Acute viral hepatitis–Toxin - induced hepatic necrosis–Circulatory shock
Damage to as little as 1% of liver cells raises ALT AST & ALT rise 7 to 14 days before jaundiceAST elevation can be screen for Reye's Syndrome
General Interpretation ofAST & ALT Levels (cont.)
Degree of elevation not necessarily related to severity of disease process
Levels < 500 U/liter usually mean mild illnessRatio of AST : ALT > 2 highly suggestive of
alcoholic hepatitis (unless ALT > 300, then this does not apply)
LDH usually normal or only slightly elevated with hepatitis or obstructive jaundice
Patterns of Enzyme Elevations inLiver and Biliary Diseases
DISEASE ALP AST ALT LDH
Acute Liver Injury 4 - 10 X >20 X >20 X +/-
Alcoholic hepatitis 2 - 4 X 4 - 10 X 2 - 4 X +/-
InfectiousMononucleosis
2 - 10 X 10 - 20 X 10 - 20 X 2 - 10 X
Cholestaticjaundice
10 - 20 X 4 - 10 X 4 - 10 X +/-
Primary or Secon. cancer
10 - 20 X 4 - 10 X 4 - 10 X 4 - 20 X
Primary biliarycirrhosis
10 - >20 X 4 - 10 X 4 - 10 X 2 - 4 X
Alcoholic fattyliver
2 - 4 X 2 - 4 X +/- +/-
Cirrhosis 2 - 4 X 2 - 4 X 2 - 4 X 2 - 4 X
Chronic activehepatitis
2 - 4 X 10 - 20 X 4 - 10 X 2 - 4 X
Time pattern of serum transaminases
Bilirubin MetabolismOriginates from breakdown of heme (from
hemoglobin, myoglobin, & cytochromes) into biliverdin which is reduced to form bilirubin
Can be produced by most cellsFree (unconjugated) bilirubin enters plasma from
sites of production–Is tightly bound to albumin–Not filtered at glomerulus (not excreted in urine)–Taken up by hepatocytes–Conjugated in microsomes by enzyme bilirubin glucuronyl transferase
–Bilirubin diglucuronide (water soluble) then excreted via bile
Disposition of ConjugatedBilirubin
Enters intestine via bileFurther reduced by colonic bacteria to
stercobilinogen / urobilinogen, which is spontaneously oxidized to brown bilin pigment (accounts for normal stool color)
Some of this pigment undergoes enterohepatic cycling
Trace amounts excreted in urine as urobilinogen, which autooxidizes to urobilin
"Direct" versus "Indirect" Bilirubin
"Indirect" = unconjugated (non- liver metabolized)–Is nonmiscible with aqueous diazonium salts–So solvent such as methyl alcohol is needed to render it water soluble, permitting a color reaction
"Direct" = conjugated (acted upon by liver cells)–Reacts directly with diazo reagents to make a measureable color change
Normal serum total bilirubin is 0.5 to 1.2 mg/dl (< 20 % unconjugated)
Bilirubin metabolism
Bilirubin metabolism in hepatic disease
Bilirubin metabolism in extra- hepatic obstruction
Causes of Jaundice fromUnconjugated
HyperbilirubinemiaPigment loading
–Hemolytic anemia–Extravascular blood (surgery or trauma)–Liver disease (unable to conjugate)
Gilbert's Syndrome–Usually benign–Bilirubin levels elevate with fasting
Crigler-Najjar Syndrome–If homozygous is severe & needs liver transplantation
Jaundice from ConjugatedHyperbilirubiinemia
Usually reflects cholestasis–Retention of bilirubin & bile salts–Can be intra- or extra- hepatic cause–Urine is dark brown (from conjugated bilirubin)–Urine froths if shaken (from detergent action of bile acids)–Patients often have pruritis from bile acids
Intrahepatic Causes ofConjugated
Hyperbilirubinemia
Hepatocellular injuryBiliary atresiaPrimary biliary cirrhosisSteroids (especially estrogens)Space - occupying hepatic lesionsDubin-Johnson Syndrome
Extrahepatic Causes ofConjugated Hyperbilirubinemia
CholedocholithiasisCaroli's DiseasePostoperative biliary tract stricturesSclerosing cholangitisCholangiocarcinomaPancreatitisAmpullary or pancreatic cancerCompression from adjacent cystsParasites
Other Tests to Consider forEvaluation of Liver Disease
Protime–Measures presence of liver-synthesized vitamin K dependent factors II, VII, X–Factor VII has half life < 12 hours–Indicates significant liver dysfunction if prolonged > 2 seconds
Serum albumin–Normal level 3.5 to 5 g/dl–Synthesized exclusively in liverMax. synthesis is 25 g/day (half life is up to 20 days)
Serum globulin–Levels often > 2 g/dl (normal < 1.1 g/dl) with chronic liver disease
Gamma glutamyl transpeptidase
Gamma Glutamyl Transpeptidase(GGTP)
Found in liver, kidney, pancreas, heart, brain
Elevates in cholestatic disordersInducible by many drugsHalf life 26 daysIf GGTP level is normal, it suggests a
concurrent ALP elevation is from bone or placenta
Can be elevated in non-liver disorders (other LFT's are then normal)
Additional Tests to Consider ToRule Out Specific Liver
DisordersAlpha-1-antitrypsin level
–Rule out alpha-1-antitrypsin deficiency–These patients can have CAH & COPD–Is autosomal recessive ; relatives should be screened
Serum ceruloplasmin–Rule out Wilson's Disease–Should confirm with liver biopsy–Is treatable
Serum iron / TIBC–Rule out hemochromatosis ; also treatable
Elevated AST
Algorithm for evaluation of elevated alkaline phosphatase
Hepatitis A Serologies
Hepatitis A IgM antibody (IgM anti-HAV)–If positive, represents current or recent acute hepatitis A–Persists typically 4 to 6 months (but up to 12) post infection
Hepatitis A total antibody (total anti-HAV)–Tests IgM & IgA early, and mainly IgG later
Time course of hepatitis A serologies
Hepatitis B Serologies
Antibody to hepatitis B surface antigen (anti-HBs)–If present indicates :
ƒ Prior hepatitis B, now immuneƒ Or prior hepatitis B vaccinationƒ Or recent hepatitis B immune globulin prophylaxis
–If HBsAg also present, indicates chronic hepatitis B (carrier)
Hepatitis B surface antigen (HBsAg)–If present, indicates acute or chronic hepatitis B and patient is infectious
Hepatitis B Serologies (cont.)
Hepatitis B e antigen (HBeAg)–If present, indicates acute or chronic hepatitis B with active viral replication
Antibody to hepatitis B e antigen (anti-HBe)–Indicates suppression of hepatitis B viral replication
Hepatitis B Serologies (cont.)
Hepatitis B core IgM antibody (IgM anti-HBc)–Indicates current or recent hepatitis B (in past 4 to 6 months), or chronic hepatitis B with active viral replication (less common)
Hepatitis B core total antibody (total anti-HBc)–Just indicates prior hepatitis B infection, but does not indicate infectivity or chronicity
Time course of acute hepatitis B serologies
Time course of chronic hepatitis B serologies
Serologies with hepatitis D superinfection
Serologies with acute hepatitis D coinfection
Hepatitis C SerologiesHepatitis C antibody by enzyme immunoassay (anti-
HCV by EIA)–Indicates chronic hepatitis C ( rarely detectable for acute hepatitis C)
Hepatitis C antibody by recombinant immunoblot assay (anti-HCV by RIBA)–Indicates chronic hepatitis C (useful for evaluating suspected false positive anti-HCV by EIA)
Hepatitis C RNA by polymerase chain reaction (HCV RNA by PCR)–Indicates acute or chronic hepatitis C
These antibodies do not confer protection against infection
Lab Charges for Liver Function Tests at Hershey
Med Center"LFT panel" (ALP, AST, total bili) : $18ALT alone : $10AST alone : $10Hepatitis serologies :
–HCV antibody : $42–HAV antibody : $37–HBc antibody : $30–HBsAg : $30–anti-HBs : $43