Laboratory Medicine Infectious Disease

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Laboratory MedicineInfectious Disease

• Brenda Beckett, PA-C
• Clinical Assessment II

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Infectious Disease

• Urinalysis
• Serum serologies (antibody testing)
• Hepatitis, others
• Cultures bacterial, viral
• Rapid antigen testing
• OP
• Nosocomial infections
• CBC results with viral vs bacterial infection

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Specimen Collection

• Urinalysis - clean catch used if culture is
  needed.
• Reflex testing - microscopic or culture if UA
  abnormal
• Proper collection of cultures

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Urinalysis

• Specimen type (clean catch, catheter, suprapubic
  aspiration, U-bag (nonsterile)
• Gross analysis - color, clarity
• Dipstick
• Microscopic - cellular elements
• Culture if indicated if infection is possible
  from dipstick or microscopic results

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Urinalysis

• Color Normal straw, light yellow.
• Amber/orange bilirubin, urobilinogen
• Red blood
• Other colors
• Clarity Normal clear
• Hazy
• Cloudy
• Artifact or cellular elements

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Urine Dipstick

• Protein Usually in form of albumin or globulins.
  
• Trace amounts in DM associated with increased
  mortality due to diabetic nephropathy.
• Globulins (Bence-Jones) associated with multiple
  myeloma
• Large amounts in nephrotic syndrome

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Urine Dipstick

• pH Normal 5-9, usually around 6. Acidotic or
  alkalotic can be due to diet, medication, disease
  or metabolic changes. Some bacteria incr. pH
• Specific Gravity Normal 1.010-1.025. Weight of
  particles in solution, correlates with
  osmolality.

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Urine Dipstick

• Bilirubin Increased in obstructive biliary
  disease, hepatocellular injury. Not incr in
  hemolytic jaundice.
• Urobilinogen Formed by bacterial conversion of
  conj. Bilirubin in intestine. Incr in
  hepatocellular injury and jaundice, not
  obstructive biliary disease. Also increased in
  CHF with liver congestion, cirrhosis, hepatitis.

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Urine Dipstick

• Blood Detects blood hemoglobin.
• Can cross react with myoglobin.
• Increased in hemolysis, GU tract cancer, UTI,
  calculi, coagulopathies, glomerulonephritis.

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Urine Dipstick

• Glucose Present if serum glucose is gt 180
  mg/dL. Increased in DM.
• Ketones Screening for ketoacidosis in diabetics.
  Increased in starvation, fever, pregnancy.

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Urine Dipstick

• Leukocyte Esterase Enzyme released by WBCs.
  Marker of infection or inflammation
• Nitrite Urine nitrates are converted to nitrite
  by some bacteria (E. coli, Klebsiella, Proteus,
  etc.)

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Microscopic

• Done if dipstick abnormal
• Detects cellular elements
• WBC
• RBC
• Bacteria
• Epithelial cells if contaminated sample, or
  tubules sloughing
• Casts, crystals

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Urine culture

• Semi-quantitative
• gt100,000 colonies/ml indicative of infection
• gt10,000 colonies/ml in symptomatic,immunosuppresse
  d or abx treated patients
• Lower numbers suprapubic (gt150)

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Serology

• Testing serum to determine antibody levels.
• Used for many viruses and other infectious agents
• IgM - early infection
• IgG - lifelong, immunity

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Hepatitis - Causes

• Drugs antihypertensives, statins, antibiotics,
  others.
• Toxic agents acetaminophen, alcohol, others.
• Viruses Hepatitis A (HAV), B (HBV), C (HCV)
  commonly. Uncommon EBV, CMV, measles, rubella,
  etc.

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Liver Function Tests

• Serum Aminotransferases (ALT and AST)
• Serum and urine Bilirubin
• Serum Alkaline Phosphatase
• Additionally LDH, GGTP, Albumin, Prothrombin Time

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Liver Function Tests

• ALT Alanine Aminotransferase
• AST Aspartate Aminotransferase
• Inflammation and cell necrosis
• Most sensitive marker of liver injury (from
  infections, toxins, autoimmunity, etc)

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Bilirubin

• Hemoglobin breakdown product
• Conjugated by liver, excreted in bile, eliminated
  in urine
• Bilirubin increased in
• Biliary tract obstruction (tumor, stone,
  pancreatitis)
• Inflammation (hepatitis)
• Hemolysis (Gilberts syndrome)

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Bilirubin

• Bilirubinuria occurs in both inflammation and
  obstruction (but not hemolysis)
• Jaundice results when levels exceed 2.5 mg/dl
• In viral hepatitis, bilirubin not always
  elevated, therefore
• Elevated serum bilirubin is neither sensitive nor
  specific for viral hepatitis

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More Liver Function Tests

• Serum albumin decreased in cirrhosis and severe,
  fulminant disease
• Prothrombin time Prolonged in severe liver
  disease (vitamin K deficiency)
• LDH (lactate dehydrogenase) non specific, not
  very useful.
• ALKP sensitive marker of biliary tract
  obstruction, mildly elevated in viral hep.

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Lab Findings

• ALT usually gt8x upper limit of normal
• ALT usually elevated gtAST
• ALKP modestly elevated
• Bilirubin normal to highly elevated
• These are quick tests if you suspect hepatitis.
• If elevated, proceed to serology testing

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Hepatitis A Serology

• HAV IgM rises early in illness, will remain
  positive for up to six months.
• HAV IgG will appear soon after IgM and remain
  elevated for years.
• Most common cause of acute viral hepatitis (AVH),
  no chronicity, no carrier state

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Hepatitis A Serology

• Testing for Hep A includes HAV Total (IgG and
  IgM), and HAV IgM. So,
• If someone has a positive HAV Total and an
  positive HAV IgM, they have a current infection.
• If someone has a positive Total and a negative
  IgM, they had a past infection or passive
  immunity (vaccination).

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Hepatitis B

• Second most common cause of acute viral hepatitis
• Most complex hepatitis virus -infective particle
  made up of viral core plus an outer surface coat
• 5-10 become chronic, lead to cirrhosis,
  hepatocellular cancer

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Hepatitis B Serology

• HBsAg First evidence of infection, persists
  through clinical illness.
• Anti-HBs Antibody to HBsAg appears after
  clearance of HBsAg and after vaccination (titer
  gt10 mU/mL).
• Neg HBsAg and pos Anti-HBs means recovery from
  HBV infection, noninfectivity and immunity.

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Hepatitis B Serology

• Anti-HBc
• IgM anti-HBc appears shortly after HBsAg.
  Indicates acute hepatitis. Persists for 3-6
  months or longer. May appear during flares of
  chronic HBV.
• IgG anti-HBc appears during acute HBV but
  persists indefinitely, whether recovery or
  chronic hepatitis occurs.

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Hepatitis B Serology

• HBeAg A soluble protein found in HBsAg positive
  patients. Indicates viral replication and
  infectivity. Appearance beyond 3 months indicates
  increased likelihood of chronicity.
• HBV DNA Parallels presence of HBeAg, more
  sensitive and precise

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Acute Hepatitis B Course
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Hepatitis B Review

• Acute HBV HBsAg, IgM anti-HBc, Total
  anti-HBc, anti-HBs-, HBeAg.
• Chronic HBV HBsAg, IgM anti-HBc-, Total
  anti-HBc, anti-HBs-.
• Past resolved HBV HBsAg-, IgM anti-HBc-, Total
  anti-HBc, anti-HBs.
• Vaccination (immunity) anti-HBs.

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Hepatitis C

• Chronicity common (gt70)
• Prolonged viremia
• Aminotransferases elevated off and on (can have
  ALT gt7x normal)
• Diagnose with Anti-HCV EIA
• False negatives early in disease (low
  sensitivity)
• False positives with elevated gamma glob (low
  specificity)

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Hepatitis C Serology

• Positive Anti-HCV EIA needs confirmation
• HCV RIBA (Recombinant Immunoblot Assay) confirms
  EIA. Does not distinguish between past/present
  infection. Being replaced by HCV-RNA
• Liver Biopsy

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Hepatitis C Serology

• HCV-RNA by RT-PCR.
• Most sensitive test
• Diagnose acute infection prior to seroconversion
• May be intermittent (neg does not mean no
  disease)
• Qualitative and quantitative tests
• Response to therapy

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Hepatitis C

• NO immunization
• No post exposure prophylaxis
• Chronicity common
• Different genotypes respond differently to therapy

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Other Hepatitis Viruses

• Hepatitis D (Delta).
• Due to ssRNA virus.
• Always associated with Hepatitis B.
• Acute or chronic.
• Often severe, high mortality.
• Hepatitis E. Due to ssRNA virus.
• Rare, occurs in endemic areas.

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Chronic Hepatitis

• HBV 5-10 of acute infections
• HCV - gt70 of acute infections
• HDV with HBV coinfection or superinfection
• Elevated aminotransferases for gt6 months
• My lead to cirrhosis, hepatocellular ca
• Liver transplant may be indicated

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Acute Viral Hepatitis Panel

• HBsAg
• IgM anti-HBc
• Igm anti-HAV
• Anti-HCV EIA

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Post Exposure Testing

• Source Patient
• Anti-HIV
• HBsAg
• Anti-HCV EIA
• Injured HCW
• Anti-HIV
• Anti-HCV EIA
• Anti-HBs

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Review of Hepatitis Serology

• http//www.cdc.gov/hepatitis/
• Excellent website with graphic representation of
  each type of viral hepatitis, case studies (click
  on Training Resources, then Viral Hepatitis
  Online Serology Training)

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HIV testing

• ELISA antibody (screening)
• Western Blot (confirmation)
• RNA PCR (viral load)
• CD4 count and

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LYME Antibodies

• Lyme ab. IgM and IgG, screening with ELISA
  testing. Confirm with WB
• Poor sensitivity/specificity
• IgM 2-4 wks post infection, decline by 4-6
  months
• IgG 4-8 wks post infection, high for months or
  years
• Must correlate clinically

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Antigen testing

• Tests for the actual infectious agent
• Example Some Hepatitis testing
• Rapid antigen tests Rapid strep, Rapid flu, C.
  diff, etc. Test for a protein or other marker on
  the bacteria or virus, not a full culture

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Stool Testing

• OP, will determine if there are parasites
  present in feces. May need more than one sample,
  not always shedding.
• Culture tests for Salmonella, Shigella,
  Campylobacter, E.coli 0157
• WBC, occult blood (Guiac)
• C. diff - rapid antigen test

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Giardia
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Viral Cultures

• Viruses are slow to grow in culture medium, may
  take weeks for a result.
• Therefore, serology is utilized more often.
• May see herpes culture ordered to confirm
  outbreak.

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Bacterial Cultures

• Sterile vs nonsterile site
• Normal flora
• Aerobic vs anaerobic
• Gram stain is routinely performed on cultures
  from certain sites sputum, wound, CSF, etc.
• Urine culture is semiquantiative others isolate
  bacterial colonies

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Common Specimens

• Eye swab conjunctiva, corneal scrapings
• FB IV cath tips, prosthetic heart valves, IUD,
  etc.
• GI Gastric biopsy for H. pylori, rectal swab,
  stool for OP, culture
• Genital cervical, urethral, vaginal secretions
  or swab.
• Resp sputum, lavage, nasopharynx/pharynx swab
• Tissue biopsy
• Urine clean catch, cath, suprapubic aspirate

• Abscess, pus, fluid swab or aspirate
• Bloodspecial vacutainer
• Body fluids (amniotic, pericardial, peritoneal,
  pleural, synovial) needle aspiration
• CSF lumbar puncture
• Cutaneous-skin or nail scrapings, swab of
  infection
• Ear- middle ear myringotomy, outer ear swab

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Bacterial Culture Gram stain

• Done quickly
• Only on certain sites
• Need to correlate with clinical picture
• Results will be verified by culture in 24-48 hrs,
  but can start empirically on antibiotics
• Report Gram /-, shape, other cellular elements
  (WBC, epithelials, etc)

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Gram Stain G
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Gram Stain G-
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Bacterial Cultures

• Most streak for isolation
• Plated on specific media for site of culture
• Grown in appropriate environment
• Will only be grown anaerobically if requested

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Streak for isolation
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Urine culture
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Bacterial Cultures

• Sensitivities if bacteria is a pathogen
• Antibiotics tested vary from lab to lab,
  depending on g or g-
• Certain species do not have sensitivities
  performed. Ex Strep, usually sens to penicillins
  so no sensitivities performed
• Hospital antibiogram common bacteria and their
  susceptibilities

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Beta Hemolysis
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Alpha, Beta Hemolysis
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Blood Culture
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Nosocomial Infections

• Originate in hospitals
• Account for tens of thousands of deaths per year
• 5-10 of hospitalized patients
• Due to
• Prevalence of pathogens
• Compromised hosts
• Effective transmission

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Nosocomial Infections

• Primary pathogens
• Enterococcus (VRE)
• E. coli
• Pseudomonas
• Staph Aureus (MRSA)
• C. diff
• Acquire antibiotic resistance
• Become normal flora for hospital workers
• Common sites urinary tract, wounds, respiratory,
  skin, blood, GI

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CA MRSA

• Community acquired MRSA
• Athletes, children, military recruits, close
  living quarters
• Not hospitalized or in long-term care

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WBC overview

• Viral vs. bacterial infection
• Viral lymphocyte response (T, B or NK). May have
  slightly elevated or suppressed total WBC count
• Bacterial Neutrophil response with early forms
  (bands). Often higher total WBC
• Sepsis
• Neutropenia or neutrophilia, immature forms