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Laboratory Medicine Infectious Disease

Learn about infectious disease diagnosis through urine and blood tests, including serologies and cultures. Understand hepatitis causes and liver function tests. Detailed guidance on interpreting urinalysis results for infections.

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Laboratory Medicine Infectious Disease

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  1. Laboratory MedicineInfectious Disease Brenda Beckett, PA-C Clinical Assessment II

  2. Infectious Disease • Urinalysis • Serum serologies (antibody testing) • Hepatitis, others • Cultures: bacterial, viral • Rapid antigen testing • O&P • Nosocomial infections • CBC results with viral vs bacterial infection

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

  4. 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

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

  6. 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

  7. 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.

  8. 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.

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

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

  11. 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.)

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

  13. Urine culture • Semi-quantitative • >100,000 colonies/ml indicative of infection • >10,000 colonies/ml in symptomatic,immunosuppressed or abx treated patients • Lower numbers suprapubic (>150)

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

  15. 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.

  16. Liver Function Tests • Serum Aminotransferases (ALT and AST) • Serum and urine Bilirubin • Serum Alkaline Phosphatase • Additionally: LDH, GGTP, Albumin, Prothrombin Time

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

  18. 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 (Gilbert’s syndrome)

  19. 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

  20. 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.

  21. Lab Findings • ALT usually >8x upper limit of normal • ALT usually elevated >AST • ALKP modestly elevated • Bilirubin normal to highly elevated • These are quick tests if you suspect hepatitis. • If elevated, proceed to serology testing

  22. 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

  23. 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).

  24. 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

  25. 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 >=10 mU/mL). • Neg HBsAg and pos Anti-HBs means recovery from HBV infection, noninfectivity and immunity.

  26. 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.

  27. 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

  28. Acute Hepatitis B Course

  29. 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+.

  30. Hepatitis C • Chronicity common (>70%) • Prolonged viremia • Aminotransferases elevated off and on (can have ALT >7x normal) • Diagnose with Anti-HCV EIA • False negatives early in disease (low sensitivity) • False positives with elevated gamma glob (low specificity)

  31. 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

  32. 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

  33. Hepatitis C • NO immunization • No post exposure prophylaxis • Chronicity common • Different genotypes respond differently to therapy

  34. 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.

  35. Chronic Hepatitis • HBV – 5-10% of acute infections • HCV - >70% of acute infections • HDV – with HBV coinfection or superinfection • Elevated aminotransferases for >6 months • My lead to cirrhosis, hepatocellular ca • Liver transplant may be indicated

  36. Acute Viral Hepatitis Panel • HBsAg • IgM anti-HBc • Igm anti-HAV • Anti-HCV EIA

  37. Post Exposure Testing • Source Patient: • Anti-HIV • HBsAg • Anti-HCV EIA • Injured HCW: • Anti-HIV • Anti-HCV EIA • Anti-HBs

  38. 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”)

  39. HIV testing • ELISA antibody (screening) • Western Blot (confirmation) • RNA PCR (viral load) • CD4 count and %

  40. 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

  41. 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

  42. Stool Testing • O&P, 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

  43. Giardia

  44. 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.

  45. 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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