Download ID LABS

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
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

Acute Hepatitis B Course
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 antiHBc-, 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

Giardia
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

Common Specimens
Abscess, pus, fluid –
swab or aspirate
Blood–special 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
Eye – swab conjunctiva,
corneal scrapings
FB – IV cath tips, prosthetic
heart valves, IUD, etc.
GI – Gastric biopsy for H.
pylori, rectal swab, stool for
O&P, culture
Genital – cervical, urethral,
vaginal secretions or swab.
Resp – sputum, lavage,
nasopharynx/pharynx swab
Tissue – biopsy
Urine – clean catch, cath,
suprapubic aspirate
Bacterial Culture – Gram stain
Done quickly
 Only on certain sites
 Need to correlate with clinical picture
 Results will be verified by culture in 2448 hrs, but can start empirically on
antibiotics
 Report: Gram +/-, shape, other cellular
elements (WBC, epithelials, etc)

Gram Stain: G+
Gram Stain: G-
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

Streak for isolation
Urine culture
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

Beta Hemolysis
Alpha, Beta Hemolysis
Blood Culture
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
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
CA MRSA
Community acquired MRSA
 Athletes, children, military recruits, close
living quarters
 Not hospitalized or in long-term care

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