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Laboratory Medicine Infectious Disease. Brenda Beckett, PA-C Clinical Assessment II. Infectious Disease. Urinalysis Serum serologies (antibody testing) Hepatitis, others Cultures: bacterial, viral Rapid antigen testing O&P Nosocomial infections
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Laboratory MedicineInfectious Disease Brenda Beckett, PA-C Clinical Assessment II
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
Specimen Collection • Urinalysis - clean catch used if culture is needed. • Reflex testing - microscopic or culture if UA abnormal • Proper collection of cultures
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
Urinalysis • Color: Normal = straw, light yellow. • Amber/orange = bilirubin, urobilinogen • Red = blood • Other colors • Clarity: Normal = clear • Hazy • Cloudy • Artifact or cellular elements
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
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.
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.
Urine Dipstick • Blood: Detects blood & hemoglobin. • Can cross react with myoglobin. • Increased in hemolysis, GU tract cancer, UTI, calculi, coagulopathies, glomerulonephritis.
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.
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.)
Microscopic • Done if dipstick abnormal • Detects cellular elements • WBC • RBC • Bacteria • Epithelial cells – if contaminated sample, or tubules sloughing • Casts, crystals
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)
Serology • Testing serum to determine antibody levels. • Used for many viruses and other infectious agents • IgM - early infection • IgG - lifelong, immunity
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.
Liver Function Tests • Serum Aminotransferases (ALT and AST) • Serum and urine Bilirubin • Serum Alkaline Phosphatase • Additionally: LDH, GGTP, Albumin, Prothrombin Time
Liver Function Tests • ALT – Alanine Aminotransferase • AST – Aspartate Aminotransferase • Inflammation and cell necrosis • Most sensitive marker of liver injury (from infections, toxins, autoimmunity, etc)
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)
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
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.
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
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
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).
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
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.
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.
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
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+.
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)
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
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
Hepatitis C • NO immunization • No post exposure prophylaxis • Chronicity common • Different genotypes respond differently to therapy
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.
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
Acute Viral Hepatitis Panel • HBsAg • IgM anti-HBc • Igm anti-HAV • Anti-HCV EIA
Post Exposure Testing • Source Patient: • Anti-HIV • HBsAg • Anti-HCV EIA • Injured HCW: • Anti-HIV • Anti-HCV EIA • Anti-HBs
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”)
HIV testing • ELISA antibody (screening) • Western Blot (confirmation) • RNA PCR (viral load) • CD4 count and %
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
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
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
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.
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