Biostatitics - Review Flashcards
Recall bias
results from inaccurate recall of past exposure
- applies mostly to retrospective control studies
- people who have suffered adverse effects are more likely to recall risk factors than those who don’t
Referral bias
- ocurs when the case and control populations differ due to admission or referral pracrices
- example, study involving cancer risk performed at cancer research hospital may enroll cases referred all over the nation however, hospitalized control
Detection bias
refers to risk factor itself may itself may lead to intensive investigation and may increase probability of finding disease
- patients who smoke may undergo increased imaging due to smoking status
Lead time bias
occurs when screening test diagnoses a disease earlier than it would have appeared by natural history so time from diagnosis until death appears longer
- affected studies may not accurately reflect improvement in health
Allocation bias
results from how the treatment and control are assembled. May occur if subjects are assigned to study groups of clinical trial in a non-random fashion
Hawthorne effect
tendency of study population to affect outcome due to knowledge of being studies
Berkson’s bias
selecting hospitalized patients as control group
Pygmalion effect
describes researcher’s effect in the efficacy of treatment that can potentially affect outcome
Cystinuria
caused by defect in renal proximal tubules which result in decreased resorption of amino acid cysteine
- renal stones at young age
- hexagonal cystine crystals
Sodium cyanide nitroprusside tests
detects cystine’s sulfhydryl groups
- turns purple
Primary oocytes
- developed by 5th month of gestation
- arrested in PROPHASE of meiosis I
Secondary oocytes
- arrested in METAPHASE of meosis II prior to fertilization
Sx: Simultaneous development of stroke, foot/intestinal ischemia and renal infarction. Likely diagnosis
Embolic phenomena
- often caused by left atrial clots, left ventricular clots, valvular vegetations, and aortic sclerotic plaques
Sx: Signs of renal failure (increased creatinine) and toe gangrene/livedo reticularis. Likely diagnosis?
Atheroembolic renal disease
- cholesterol emboli obstructs renal arterioles
Sx: Urinary hestinancy, urgency, frequency, incomplete coiding, post-void leakage in men > 60 years old.
BPH
Prostate
found between pubic symphysis and anal canal
Common causes of impetigo
S. aureus and Group A Strep
Post-streptococcal glomerulonephritis
- follows pharyngitis or skin infection (impetigo)
Conditions caused by incomplete obliteration of processus vaginalis
Hydrocele
Indirect inguinal canal
Hydrocele
- due to incomplete obliteration of processus vaginalis
- occurs when there is connection between scrotum and abdominal cavity that allows for leakage of fluid
Secretory phase of menstrual cycle
- occurs between ovulation and menses
- progesterone released by corpus luteum causes uterine glands to coil and secrete mucus-rich secretions and plumps up endometrium
In follicular phase, what hormone mediates endometrial proliferation?
Estrogen
- glands appear straight and narrow (small lumens)
In secretory phase, what hormone mediates endometrial proliferation
Progesterone
- glands appear dilated and coiled (wide lumens)
Best way to visualize T. pallidum
Darkfield microscopy
Cryptochordism
- undescended testes
- normal testosterone levels but low sperm (in adults)
- if uncorrected, seminiferous tubules atrophy and Sertoli cells secrete less inhibin
- increased risk of testicular cancer
Sertoli cells
- found in seminiferous tubules
- secrete INHIBIN - which inhibits FSH
- support sperm synthesis
Leydig cells
- secrete testosterone
Annovulation
- common in first five to seven years after menarche and last years before menophause
- manifests with marked menstrual in variability
FSH levels in menopause
Elevated FSH levels in menopause
Phenylepherine
alpha agonist with some selectivity for alpha 1 receptors
- would encourage urinary retention
Treatment for urinary retention
Muscarinic agent (bethanecol) or alpha-blocking agents
Finasteride
- prescribed to patients urinary retention secondary to BPH
- 5-alpha reductase inhibitor which decreases DHT, which would decrease hypertrophy of bladder
Hydronephrosis
dilation of renal pelvis and calyces due to obstruction of urine flow
- kidney enlargement and distortion, compression of papillae, and thinning of parenchyma around calyces seen
- commonly caused by BPH
Treatment for patients presenting with calcium stones with hyperoxaluria
low sodium diets
Ectopic pregnancy
- higher occurence in patients with PID
- abdominal pain, vaginal bleeding, hemorrhagic shock, and amenorrhea
- biopsy shows decidual changes but no chorionic villi
Sildenafil
inhibitor of cGMP phosphodierase
- NO and ANP use this mechanism
Signs of urethral injury
- inability to void despite sensation of full bladder
- high riding boggy prostate
- blood in urethral meatus
Injury to posterior urethra
associated with pelvic fracture
Injury to anterior urethra
associate with straddle injuries
Hormones that prevent lactation during pregnancy
Estrogen and progesterone
B-lactamase inhibitors
Clavulanic acid
Sulbactam
Tazobactam
** extend the spectrum of penicilin binding antibiotics by decreasing their destruction
Tazobactam-Piperacillin
- Tazobactam - B-lactamase inhibitor allows piperacillin to act on gram negative bacteria that would not be vulnerable to piperacillin alone
BPH
- epithelial and stromal hyperplasia, mostly in periurethral and transitional zones
- urinary retention as a result leads to increased pressure in urinary tract, nephropathy, and hydronephrosis
Organs that drain to superficial inguinal lymph nodes
- all skin from umbilicus down (up to pectinate line) drains to superficial inguinal lymph nodes
Testicular hydrocele
- when serous fluid accumulates in tunica vaginalis
- results when processus vaginalis fails to close
Contraindications to OCPs
- Prior embolic event (stroke, PE, MI)
- History of estrogen dependent tumor
- Women over 35 who smoke
- Hypertriglyceridemia
- Liver disease
- Pregnancy
Gram-negative sepsis is caused by which bacterial factor?
LPS
- it is NOT secreted by bacteria but part of outer membrane
- induces activation of macrophages leading to IL-1 and TNF-alpa
Signs of septic shock
Fever hypotension Diarrhea Oliguria Vascular compromise DIC
TNF-alpha
cytokines that induces systemic inflammatory response
- causes septic shock
Cytokines responsible for inducing systemic inflammatory response
IL-1
IL-6
TNF-alpha
Which mechanism does mifepristone use to terminate early pregnancy
Anti-progestin
Endometrial cells undergo what process upon withdrawal of progesterone
Apoptosis
Calcium oxalate/ calcium phosphate
- radiopaque
- octahedron
- most common
Magnesium struvite
- radiopaque
- resemble coffin lids (retangular prism)
Uric acid
- RADIOLUCENT
- yellow/red-brown diamond/rhombus
Cysteine
- Radiopaque
- hexagonal
- least common
Vasectomy
- transection of vas deferens
- has no effect on sperm proximal to ligation
- patients may still have viable sperm 3 months and at least 20 ejaculations
Pathogenesis of acute pyelonephritis
- vesicoureteral reflux
Pathogenesis of lower UTIs
- suppression of indigenous flora
- colonization of distal urethra by gram - rods
- attachment of gram - pathodesnt to bladder mucosa
Sx: Adnexal mass in elderly female
- Likely ovarian malignancy
Serum marker for recurrence of ovarian malignancy
CA-125
Sx: fever, maculopapular rash and symptoms of ARF, 1-3 week after beginning treatment with B-lactam antibiotic
suggests interstitial neprhitis
- peripheral eosinophilia and eosinophiluria
- symptoms will stop after cessation of medication
Serum and urine levels associated with calcium kidney stone
- Normocalcemia
- Hypercalciuriae
Standard treatment for N. gonorrthoae
- Ceftriaxone ( for the N. gonorrohoe) + Doxycycline or Azithromycin for possible co-infection of C. trachimatis
Mechanism of OCPs
- doses of estrogen and progesterone
decrease synthesis of FSH and LH in anterior pituitary thus decreasing gonadotropin levels
Type I error
when researchers reject a TRUE null hypothesis
b/b+d (kind of like specificity)
Alpha - probability of making a type 1 error, typtically set at p = 0.05
Type II
when researchers accept a FALSE null hypothesis
c/a+c - (kind of like sensitivity)
B - probability of commiting type 2 error
Alpha (in terms of biostatistics)
maximum probability of committing a type I error
typically accepting p = 0.05
Beta ( in terms of biostatistics)
maximum probability of committing a type II error (accepting a false null hypothesis)
Power
(1 - Beta)
probability of rejecting a null hypothesis when it is truly false
Observer Bias
to prevent patient or researcher expectancy from interfering with determining outcome
- often prevented by blinding patients OR both patients and physicians from the groups
Selection bias
results from manner in which people are selected for the study, or from the selective losses from follow-up
Odds Ratio
ad/bc
Relative Risk
a/(a+b) - c/(c+d)
Prospective cohort study
initially a group of subjects is selected and their exposure status is determined. The cohort is then followed for a certain amount of time and observed for development of outcome
Retrospective cohort study
exposure status is determied retrospectively and then that person is tracked from that point of time, using medical records
Cross sectional study
simultaneous measure of exposure and outcome
- uses surveys
Case control
selecting patients with particular disease (cases) and with that disease (controls) and then determining exposure status
