Lab tests in primary care Flashcards
Sensitivity
The ability of a test to correctly identify those who have the disease “true positive rate”
Specificity
The ability of a test to correctly identify those who do not have the disease “true negative rate”
Positive predictive value
Describes the likelihood that a person whose test shows a positive result, actually has the disease
Negative predictive value
Describes the likelihood that a person whose test showa a negative result does not have the disease
How to estimate PPV?
Demographics (age, sex) , risk factors, symptoms and signs, past medical history
What are the criteria for typical anginal pain?
1) retrosternal 2) exercise or stress related 3) relieved by nitro
Atypical angina
Two criteria
Non-anginal
one criterium
DM screening
Pat should be screened at 3-year intervals beginning at age 45y. Should be considered at an earlier age / more often if increased risk.
Risk factors of DM
- Family history of DM
- Overweight defined as BMI > 25kg/m2
- Habitual physical inactivity
- Belonging to high risk ethnic/ racial group: Pacific islanders, american-indians, african-american, asian-american, hispanic
- Previously identified IFG or IGT
- HT
- Dyslipidemic
- History of GDM or delivery of a baby weighing > 4kg
- PCOS
Abnormal test result in DM
- Further MX: glycemic, cholesterol, troponin, Ig´s
- Pat: 1) suspected disease 2) presence of sx 3) screening
- Results: ask how much abnormal?
Biologic variables that affect test results
- Biologic rhythms: circadian(daily), ultradian (24h), infradian (longer like menstruation)
- Constitutional factors: age, gender, genotype
- Extrinsic factors: 1) Posture 2) Exercise 3) Diet (caffeine) 4) Drugs 5) Alcohol 6) Pregnancy 7) intercurrent illness
What to do with abnomal test result?
- Test repating
- Other tests ordering
- Specialist / hospital referral
What is included in lab staff?
Clinical pathologist, microbiologist, hematologist
PCR
- Genetic material, DNA and RNA
- Is a type of nucleic acid amplification technology
- Improved Dx in virology, slow growing and fastidious organisms
- Polymerase is an enzyme that catalyses formation of nucleotides into DNA molecules before cell division, or RNA before protein synth
- Used for: bacterial inf, parasite, virus ass w cancer, HIV, genetic disorders (DM, breast ca), disorders of blood (thalassemia), muscle disorders
ESR
- Blood components separate faster in illness
- Determined by the effect of serum proteins on the neg. electric charge on the erythrocyte surface
- A marker of inflammation and malignant disease
- Presence of all acute phase proteins (esp. fibrinogen) as well as Ig
- Should be used for asymptomatic pat to screen for presence of disease
- Lag phase of 24-48h btw onset of inflammation and production of proteins increasing ESR. Also delay after resolution
- Norm is <20 mm/h, (adult male 17-50y = 1-10, >50y = 2-15 / female 17-50y = 3-12, >50y = 5-20)
What may be suspected in very high ESR, 100++
Giant cell arthritis, MM, TB, polymyalgia rheumatica, deep abscess, endocarditis, osteomyelitis
Low ESR <1
Idiopathic, sickle cell, polycythemia, CHF, hypofibrinogenemia, high WBC, NSAIDs, old specimen, low serum protein (CKD, liver disease)
Very high ESR + normal CRP
May indicate giant cell arteritis or polymyalgia rheumatica
CRP
- Product of acute-phase response, tissue inflammation
- Non-specific marker of inflammation and neoplastic disease
- Rise within 6h, double every 8h, reaching peak at 50h
- Can fall very rapidly but resolve w 24h half life
- > 100mg/L have 80% sens & 88% spec for bacterial inf
- 10-40mg/L has sens 69% and 54% spec for viral inf
Rules of inflammation in CRP
< 10 is norm (5 i Norge)
4-10 = mild
10- 20 = moderate
> 40 = marked
What can one use CRP for ?
1) Response to Tx 2) Activity of disease
What is CRP not affected by ? (unlike ESR)
Pregnancy
What test do you use for Adenovirus
Serum Ab levels, PCR for feces and resp specimen
Cat-scratch disorder
Serum Ab
VZV
Clinical Dx, blood w Abs/ PCR or culture from vesicle
HSV
PCR of genital lesions
Chlamydia pneumonia
Blood sample w Ab
Chlamydia trachomatis
Swabs or endotracheal aspirate for culture and PCR or urine sample
Clostridium dificile
Fresh feces, toxin and culture
CMV
blood sample Abs
EBV
Blood film (?), mono spot & Paul Bunnell, Abs to viral capsule
Hep
Blood for immunoassay for Abs and HBV Ag, PCR for viral load w HBV/HBC, genotyping to see tx benefit
HIV
Blood abs for HIV1 and HIV2, detuned ELISA-> time of infection, CD4 count, HIV viral load
Influenza
Blood Abs 2-4w serum. Has low sens and unhelpful for tx as Dx is retrospective. PCR of nasal swabs
Mumps
Blood abs -> decide immune status and IgM assay
- IgG in CSF= meningitis
Mycoplasma pneumonia
blood abs, IgM
Parvivirus B19
blood abs, suspected 5th disease
Pat w fine maculopapular rash. Serology can be performed for the following:
Measles (IgM), Rubella, Parvovirus B19, Echovirus, EBV, CMV, (Ross river virus, Barmah forrest virus) Dengue fever
N. gonorrhea
Culture (urethral, cervical, rectal, pharyngeal), PCR on swabs or urine
Syphilis
Serology ( RPR, TPHA, FTA-ABS, EIA)
Trichomonas
Microscopy from vaginal swab
Lymphogranuloma venerum
Chlamydia serology, LN biopsy
Chancroid
Microscopy/culture for Hempphilus ducrei
Granuloma inguinale (Klebsiella)
biopsy
UTI
- WBC > 10 pr uL is abnormal = local inf
- Higher counts have greater significance
- Epithelial cells = possibly contamination in female
- Culture: >10^5 per mL are more significant
Serum level of iron decrease
Falls gradually below normal when iron in body decrease after reserves bc exhausted. Level of transferrin then increase (iron transport)
Norm iron
14-30 umol/L
Transferrin
A carrier protein that binds most of the iron in serum. TIBC = total iron binding capacity = total amount of iron that can be bound to serum protein
Transferrin saturation
Which extent the iron binding sites on transferrin are occupied by iron 20-50 % (markedly elevated in hemochromatosis)
Serum Fe
Direct relationship to the amount of iron stores in the body. 20-250ug/L in males and 10-150 in female
Liver function tests
Consists of plasma bilirubin, albumin, plasma transferase, plasma alkaline phosphatase( ALP), gamma-glutamyl-transferase (GGT)
Increased plasma bilirubin
Unconjugated: breakdown of RBC
Conjugated: after metabolism in liver
Albumin
Transport protein produced in liver and maintains oncotic pressure. Has half life of 20 days. Norm 3,5-5,5 g/dL. Reduced w advancing liver disease, nephrotic sd, protein loosing enteropathy, malnutrition, and some inflammatory diseases. Elevation is unusual except in dehydration.
ALP
Present on surface of hepatocyte and in bile canaliculi and duct. Not specific to liver, but indicator of cholestasis = obstruction, infiltration and cirrhosis
GGT
Present in bile canaliculi. Raised w cholestasis, other liver disease and drug/ alcohol intake
Acute hepatitis jaundice
ALP norm to <3 x norm and ALT/AST 10-100x normal
Obstruction jaundice
ALP >3x norm, ALT/AST <10 x norm
Alcohol abuse
1) GGT limited sens/spec 2) MCV: macrocytosis but limited sens/spec 3) Carbohydrate deficient transferin
TFT
- TSH have high sensitivity
- T3 = serum free tri-iodothyrine
- T4 = thryoxine
- TPO-anti = thyroid peroxidase antibodies
- Anti-thyroglobulin abs
- Thyroxine-binding globulin and thryoglobulin
Hypernatremia
> 145mmol/L
Causes: Water depletion (DI), diarrhea, corticosteroid excess, excess IV hypertonic Na solution
Clinical: thirst, confusion, oliguria, orthostatic hypotension, muscle twiching/cramps, seizure, delirium, hyperthermia, coma
Hyponatremia
<135mmol/L
Causes: Water retention, kidney failure, GI loss (diarrhea/ vomiting), drugs/diuretics/ACEi
Clinical: lethargy, confusion, mental change, convulsions, coma, death
Elevated amylase
Pancreas: Acute/chronic pancreatitis, pseudocyst, cancer, trauma
Nonpancreatic: Salivary glans disorder, intestinal perforation/ischemia/obstruction, DKA, perforated peptic ulcer, ruptured ectopic pregnancy, renal failure, macroamylasemia, pregnancy
Elevated lipase
Acute/chronic pancreatitis, DKA, small bowel oust., acute cholecystitis(!) , renal failure
BUN
7-18 mg/dL. Elevated in hypovolemia, increased protein intake, corticosteroid use, hyper catabolism, GI bleed
Renal function:
- 10:1 suggest intrinsic renal pathology
- >20: 1 suggest prerenal or postern cause.
Reduced in severe liver disease, malnutrition, SIADH
ANA very useful for dx of
SLE, systemic sclerosis
ANA somewhat useful for dx of
Sjögren, polymyositis-dermatositis
ANA useful for monitoring Px
Drug associated lupus, MCTD, autoimmune hepatitis
ANA not useful or has no proven value for Dx, monitoring or Px in
RA, MS, thyroid dis, inf, ITP, fibromyalgia
Hyperkalemia
K>5mmol. Causes: Kidney failure, acidosis, Addison, excessive intake of K, drugs (spironolactone, ACEI, NSAID)
Clinical: muscle weakness, flaccid paralysis, cardiac arrest, peaked T-wave on ECG, decreaset QT, increased PR -> arrhythmia
Hypokalemia
<3,5. Causes: kidney disease, GI loss (V/D), alkalosis, mineralocorticoid excess, loss in ECF > ICF ( burns, trauma) decreased intake, drugs (furosemide, thiazide)
Clinical: Lethargy, muscle weakness, cramps, confusion, flaccid paralysis, tetany, coma,
