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How and When to Order Blood Tests Tammy Pifer Than, MS, OD, FAAO Carl Vinson VAMC Dublin, GA tammy.than@va.gov Getting the Job Done... PCP External laboratory In-office sampling is it ok? Before You Order Tests... good case hx narrow ddx avoid “shot gun” approach

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How and When to Order Blood Tests


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how and when to order blood tests

How and When to Order Blood Tests

Tammy Pifer Than, MS, OD, FAAO

Carl Vinson VAMC

Dublin, GA

tammy.than@va.gov

getting the job done
Getting the Job Done...
  • PCP
  • External laboratory
  • In-office sampling
    • is it ok?
before you order tests
Before You Order Tests...
  • good case hx
  • narrow ddx
  • avoid “shot gun” approach
  • comprehensive ocular exam
if you order tests
If You Order Tests...
  • interpret
    • Laboratory Tests and Diagnostic Procedures
      • 4th edition - 2004
      • Chernecky and Berger
        • includes Herbal interactions
      • ISBN 0721603882
      • $41.95
  • communicate
  • treat
  • refer
random blood glucose
Random Blood Glucose
  • note when patient ate last
    • e.g. 220 mg/dL pp 3 hours
    • pp = post-prandial
  • diabetic if:
    •  200 mg/dL with symptoms
  • can do in-office
  • encourage patients to do this!
glycosylated hemoglobin
Glycosylated Hemoglobin
  • HbA1c
  • checks long-term control
  • glycosylated HgB stays with RBC for its entire life
  • not diagnostic test?
  • normal = 4.3-6.1%
  • diabetic goal < 7.0%
  • ask patients!
fasting plasma glucose
Fasting Plasma Glucose
  • fluctuating vision
    • get stable reading before new SpRx
  • retinopathy
  • diplopia
  • vascular occlusions
  • optic neuropathy
case 1 this is an easy one
Case #1. This is an easy one!
  • 17 year old male
  • CC: eyes look “real bad”
  • Symptoms: no pain
  • Pertinent Hx: county fair last night
subconjunctival hemorrhage
Subconjunctival Hemorrhage
  • History
    • frequency
    • medications
    • activity
  • Examination
subconjunctival hemorrhage11
Subconjunctival Hemorrhage
  • Blood pressure
  • CBC with differential
  • PT (prothrombin time)
  • PTT (partial thromboplastin time)
    • or APTT (activated PTT)
  • INR (international normalized ratio)
prothrombin time pt
Prothrombin Time (PT)
  • prothrombin:
    • vitamin-K dependent glycoprotein produced by liver
    • needed for firm fibrin clot formation
  • PT – measures time for clot formation
    • reagent tissue thromboplastin and calcium are added to citrate plasma
  • avoid coffee and alcohol for 24 hours before test
prothrombin time pt13
Prothrombin Time (PT)
  • each lab has normal value
  • normal range is  2 secs
  • Adult 10-15 sec
  • International Normalized Ratio (INR)
    • standardizes PT results
    • INR = (Patient’s PT in seconds)ISI

Mean normal PT in seconds

    • ISI = international sensitivity index
    • Coumadin therapy
partial thromboplastin time ptt
Partial Thromboplastin Time (PTT)
  • evaluates how well coagulation sequence is functioning
  • time for recalcified, citrate plasma takes to clot after partial thromboplastin is added
  • Activated PTT
    • commercial activating materials used to standardize the test
    • current method of the test
  • Standardized times reported by each lab
    • < 35 seconds
cbc with differential
CBC with differential
  • routine part of health care
  • inexpensive
  • screening:
    • anemia
    • leukemia
    • infection
    • inflammation
wbc part of cbc
WBC (Part of CBC)
  • Total
    • overall number
    • first line of defense
    • decreased in aplastic anemia
    • elevated in infections, leukemia
wbc part of cbc17
WBC (Part of CBC)
  • Differential
    • 100 white blood cells
    • % of each
    • neutrophils
    • lymphocytes
    • monocytes
    • eosinophils & basophils
slide18
CBC
  • RBC count
  • hemoglobin
  • morphology
  • hematocrit
    • volume of RBC in 100 mL
    • 3 x Hgb
  • platelets
coagulation studies
Coagulation Studies
  • recurrent subconjunctival hemorrhages
  • non-traumatic hyphema
  • artery or vein occlusion
  • pre-op cataract surgery?
case 2 to treat or not to treat
Case #2. To Treat or not to Treat.
  • 34 YOWF
  • CC: HAs, double vision, dizzy
  • OHx: no trauma, LEE in 1999 - normal
  • MHx: Voltaren, Zantac
exam findings
Exam Findings
  • 20/20 OD; 20/20 OS
  • PERRL / (-)APD
  • partial 6th nerve palsy (OS)
  • visual field defects
    • superior nasal step OD
    • increased blind spot OS
fundus what s your diagnosis
Fundus: What’s Your Diagnosis?
  • papilledema
  • R/O mass
  • R/O infection
  • placing your bets...
    • Idiopathic Intracranial Hypertension
workup
Workup
  • CT or MRI
    • unremarkable
  • LP
    • normal CSF content
    • elevated pressure
management
Management
  • weight loss
  • acetazolamide
    • Diamox
  • steroids??
  • ON sheath decompression
  • LP shunt
before you prescribe diamox
Before you prescribe Diamox
  • baseline electrolytes
  • CBC with differential
    • R/O blood dyscrasias
  • monitor every 6 months
electrolytes
Electrolytes
  • Na+
    • 135.0 – 145.0 mmol/L
  • K+
    • 3.60 – 5.00 mmol/L
  • Cl-
    • 101.0 – 111.0 mmol/L
co 2 total content blood
CO2 total content blood
  • 21.0 – 31.0 mmol/L
  • Increased
    • alcoholism
    • airway obstruction
    • pneumonia
    • drugs (e.g. antacids)
  • Decreased
    • dehydration
    • Diamox
      • measures compliance - < 20 mEq/L
    • tetracyclines
sma 6
SMA-6
  • Sequential multiple analyzer (SMA)
  • automated system that analyzes multiple blood values from one tube of blood
  • SMA-6
    • Carbon dioxide
    • Chloride
    • Creatinine
    • Potassium
    • Sodium
    • Urea nitrogen
sma 7
SMA-7
  • Carbon dioxide
  • Chloride
  • Creatinine
  • Glucose
  • Potassium
  • Sodium
  • Urea nitrogen
sma 12
SMA-12
    • Albumin
    • Alkaline phosphatase
    • Aspartate aminotransferase
    • Bilirubin
    • Calcium
    • Cholesterol
    • Glucose
    • Lactate dehydrogenase
    • Phosphorus
    • Protein
    • Urea nitrogen
    • Uric acid
  • Also SMA-20
eyelid xanthoma
Eyelid Xanthoma
  • dermis infiltrated with xanthoma cells
  • yellow bilateral plaque
  • medial aspect UL
  • management:
    • cautery
    • laser
    • anything else?
lipid panel profile
Lipid Panel/Profile
  • 12 hour fasting
  • total cholesterol
  • LDL
    • Usually calculated
    • LDL = cholesterol X (HDL+Triglycerides)/2
  • HDL
  • triglycerides
  • risk for CAD
  • ratio total cholesterol / HDL
cholesterol
Cholesterol
  • over half of adults in US have cholesterol > 200 mg/dL
  • desirable: 160-200 mg/dL
  • borderline: 200-239 mg/dL
  • high  240 mg/dL
  • Outside US
    • cholesterol x 0.0259 mmoles/L (international units)
    • 200 mg/dL = 5.18 mmol/L
more numbers
More Numbers…
  • HDL
    • good  35 mg/dL
      • women probably  45 mg/dL
    •  1 mg/mL risk of CHD  2-3%
      • Helsinki Heart Study (gemfibrizol in men )
  • LDL
    • good < 130 mg/dL
    • high  190 mg/dL
  • Ratio (Total / HDL)
    • < 5:1
      • Female < 4.4
triglycerides
Triglycerides
  • normal < 200 mg/dL
    • women probably < 150
  • borderline 200-400
  • high 400-1000
  • very high > 1000
lipid panel
Lipid Panel
  • arcus
    • young patients
  • occlusive disease
  • optic neuropathy
  • xanthoma
case 338
Case #3
  • 52 YOWM
  • CC: “inferior vision OS is dim”
  • MHx: diabetic x 20 years; poor control
  • VAs: OD 20/20 OS 20/20-2
  • LEE: 6 month prior
    • two dot hemorrhages OD
initial presentation
Initial Presentation
  • OD – unremarkable
what is your tentative diagnosis
What is your tentative diagnosis?
  • 1. Anterior ischemic optic neuropathy
  • 2. Retrobulbar mass
  • 3. Papilledema
  • 4. Diabetic papillopathy
  • 5. Optic Neuritis
  • 6. Papillitis
  • 7. Other?
slide42
ESR
  • erythrocyte sedimentation rate
  • nonspecific test for inflammation
  • mm/hr
  • M: age/2
  • F: (age+10)/2
  • usually > 60 mm/hr in GCA
c reactive protein crp
C-Reactive Protein (CRP)
  • abnormal serum glycoprotein produced by liver during acute inflammation
  • disappears rapidly once inflammation subsides
  • 4 hour fast from food/fluids
  • alternative to ESR
  • more informative
    • ESR high in most elderly
    • no cross interference
  • normal: no CRP
causes of optic nerve edema
Causes of Optic Nerve Edema
  • Arteritic Ischemic Optic Neuropathy
  • Nonarteritic Ischemic Optic Neuropathy
  • Central Retinal Vein Occlusion
  • Compressive Optic Nerve Head Tumor
  • Diabetic Papillopathy
  • Infiltration of Optic Nerve Head
  • Malignant Hypertension
  • Papilledema
  • Papillitis
  • Papillophlebitis
  • Thyroid Ophthalmopathy
diabetic papillopathy
Diabetic Papillopathy
  • 0.4 – 2% of diabetics
  • characteristics
    • sectoral or total ON edema
    • ± peripapillary hemorrhages
    • ± nerve fiber layer infarcts
    • ± macular edema
  • unilateral or bilateral
    • asymmetric
diabetic papillopathy46
Diabetic Papillopathy
  • retinopathy does not need to be present
  • small optic nerve cupping
    •  0.3/0.3
  • usually associated with Type 1 DM?
  • prognosis:
    • signficant or complete recovery in several months
    • may have residual pallor and VF defect
  • pathophysiology is unclear
diabetic papillopathy47
Diabetic Papillopathy
  • Eye 2005 19:45-51
    • 6 eyes
    • Betamethasone – Subtenons’ injection
    • duration decreased from 5 months to 3 weeks
  • Am J Ophth 2004 137(6) 1151-3
    • 1 case – intravitreal triamcinolone
    • significant improvement in visual acuity
phone a friend
“Phone A Friend”
  • 40 YOBF
  • CC: “Decrease vision for 3 weeks”
  • HPI: OS worse than OD; no pain; acute
  • MHx: unremarkable
  • Meds: None
  • NKMA
phone a friend50
“Phone A Friend”
  • Entering Acuities
    • OD 20/60 PH 20/30
    • OS 20/50 PH 20/30
  • Refraction
    • OD
      • -2.00 –1.75 x 135 20/25
      • -2.00 –5.00 x 167 20/50
  • K readings…
    • OD 39.75 / 44.12 @ 095
    • OS 36.75 / 43.50 @ 095
  • Cornea
    • central corneal edema with “haziness”
what s your tentative diagnosis
What’s Your Tentative Diagnosis?
  • 1. Keratoconus
  • 2. Keratoconus with Acute Corneal Hydrops
  • 3. Corneal Ulcer
  • 4. Corneal Dystrophy / Corneal Degeneration
  • 5. Dry Eye Syndrome
  • 6. Herpes Simplex Keratitis
  • 7. Other
what was actually done
What Was Actually Done…
  • Cycloplegic
  • Muro 128 qid
  • RTC 1 day
interstitial keratitis
Interstitial Keratitis
  • cellular infiltration of the corneal stroma
  • no primary involvement of epi or endo
  • characterized by:
    • acute:
      • dense, white stromal necrosis
      • vascularization (salmon patch of Hutchinson)
    • later:
      • scarring and thinning
      • ghost vessels
interstitial keratitis54
Interstitial Keratitis
  • Syphilis (Congenital or Acquired)
  • TB
  • Lyme
  • Parasitic infection
  • HSV
  • Sarcoidosis
  • Leprosy
  • Misc.
syphilis ever had it
Syphilis: Ever Had It?
  • FTA-ABS
    • fluorescent treponemal antibody absorption test
    • ordered more frequently
    • positive even after treatment
  • MHA-TP
    • microhemagglutination treponemal pallidum test
syphilis do you have it now
Syphilis: Do you have it now?
  • RPR
    • rapid plasma reagin test
  • VDRL
    • venereal disease research laboratory test
  • Treat If:
    • (+) RPR and (+)FTA-ABS
  • What if:
    • (+)RPR and (-)FTA-ABS
slide57
PPD
  • purified protein derivative
  • TB skin test
  • inject under skin
  • check in 48-72 hours
  • positive is >10 mm wheal
  • Positive for active and inactive TB
lyme titer
Lyme titer
  • In endemic areas...
  • Normal: negative
slide59
ACE
  • angiotensin converting enzyme
  • Enzyme found primarily in lung epithelial cells
    • Some in blood vessels and renal tissue
    • Converts angiotensin I to angiotensin II, a vasopressor that also stimulates adrenal cortex to produce aldosterone
  • best for patients > 20 YO
  • helps confirm dx of sarcoidosis
    • ACE elevated in 60%
interstitial keratitis60
Interstitial Keratitis
  • Active
    • 70% of unilateral Herpes Simplex Virus
    • 60% of bilateral  Idiopathic
  • Inactive
    • 50% of bilateral  Syphilis
  • All cases
    • 20% attributed to syphilis