Updated: 4/3/2020

# 2x2 Tables (SN, SP, PPV, NPV, OR, RR)

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 Sensitivity, Specificity, PPV, NPV These 4 measures describe how well diagnostic tests capture the true presence or absence of disease  Sensitivity (SN) % with disease who test positive = a/(a+c) = TP/(TP+FN) Specificity (SP) % without disease who test negative = d/(b+d) = TN/(FP+TN) Positive predictive value (PPV)      % positive test results that are true positives = a/(a+b) = TP/(TP+FP) Negative predictive value (NPV)  % negative test results that are true negatives = d/(c+d) = TN/(FN+TN) Cut-off point may be adjusted to optimize sensitivity and specificity, which are inversely related (cut-off point with decreased sensitivity is associated with increased specificity and vice-versa)   Receiver operating characteristic (ROC) curves are a graphical depiction of a test's performance Y axis: sensitivity X axis: 1-specificity The higher the curve, the better the test This is quantified by the AUC (area under the curve); an AUC of 0.5 states that the test performs no better than chance (bad test!), whereas an AUC of 0.9 suggests a better-performing test
 Odds Ratio, Relative Risk, Attributable Risk, Absolute Risk Reduction These measures describe the relationship between a risk factor and a disease Odds Ratio (OR) odds of having disease in expose group / odds of having disease in unexposed group  = ad/bc Relative Risk (RR)    probablity of getting disease in exposed group / probability of getting disease in unexposed group = [a/(a+b)] / [c/(c+d)] Attributable Risk (AR)   risk in exposed group - risk in unexposed group = a/(a+b) - c/(c+d) Absolute Risk Reduction (ARR)   risk in control group - risk in intervention group = c/(c+d) - a/(a+b)

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Lab Values
 Blood, Plasma, Serum Reference Range ALT 8-20 U/L Amylase, serum 25-125 U/L AST 8-20 U/L Bilirubin, serum (adult) Total // Direct 0.1-1.0 mg/dL // 0.0-0.3 mg/dL Calcium, serum (Ca2+) 8.4-10.2 mg/dL Cholesterol, serum Rec: < 200 mg/dL Cortisol, serum 0800 h: 5-23Â Î¼g/dL //1600 h: 3-15 Î¼g/dL 2000 h: â‰¤ 50% of 0800 h Creatine kinase, serum Male: 25-90 U/LFemale: 10-70 U/L Creatinine, serum 0.6-1.2 mg/dL Electrolytes, serum Sodium (Na+) 136-145 mEq/L Chloride (Cl-) 95-105 mEq/L Potassium (K+) 3.5-5.0 mEq/L Bicarbonate (HCO3-) 22-28 mEq/L Magnesium (Mg2+) 1.5-2.0 mEq/L Estriol, total, serum (in pregnancy) 24-28 wks // 32-36 wks 30-170 ng/mL // 60-280 ng/mL 28-32 wk // 36-40 wks 40-220 ng/mL // 80-350 ng/mL Ferritin, serum Male: 15-200 ng/mLFemale: 12-150 ng/mL Follicle-stimulating hormone, serum/plasma Male: 4-25 mIU/mL Female: premenopause: 4-30 mIU/mL midcycle peak: 10-90 mIU/mL postmenopause: 40-250 pH 7.35-7.45 PCO2 33-45 mmHg PO2 75-105 mmHg Glucose, serum Fasting: 70-110 mg/dL2-h postprandial:<120 mg/dL Growth hormone - arginine stimulation Fasting: <5 ng/mLProvocative stimuli: > 7ng/mL Immunoglobulins, serum IgA 76-390 mg/dL IgE 0-380 IU/mL IgG 650-1500 mg/dL IgM 40-345 mg/dL Iron 50-170 Î¼g/dL Lactate dehydrogenase, serum 45-90 U/L Luteinizing hormone, serum/plasma Male: 6-23 mIU/mL Female: follicular phase: 5-30 mIU/mL midcycle: 75-150 mIU/mL postmenopause 30-200 mIU/mL Osmolality, serum 275-295 mOsmol/kd H2O Parathyroid hormone, serume, N-terminal 230-630 pg/mL Phosphatase (alkaline), serum (p-NPP at 30Â° C) 20-70 U/L Phosphorus (inorganic), serum 3.0-4.5 mg/dL Prolactin, serum (hPRL) < 20 ng/mL Proteins, serum Total (recumbent) 6.0-7.8 g/dL Albumin 3.5-5.5 g/dL Globulin 2.3-3.5 g/dL Thyroid-stimulating hormone, serum or plasma .5-5.0Â Î¼U/mL Thyroidal iodine (123I) uptake 8%-30% of administered dose/24h Thyroxine (T4), serum 5-12 Î¼g/dL Triglycerides, serum 35-160 mg/dL Triiodothyronine (T3), serum (RIA) 115-190 ng/dL Triiodothyronine (T3) resin uptake 25%-35% Urea nitrogen, serum 7-18 mg/dL Uric acid, serum 3.0-8.2 mg/dL
 Hematologic Reference Range Bleeding time 2-7 minutes Erythrocyte count Male: 4.3-5.9 million/mm3Female: 3.5-5.5 million mm3 Erythrocyte sedimentation rate (Westergren) Male: 0-15 mm/hFemale: 0-20 mm/h Hematocrit Male: 41%-53%Female: 36%-46% Hemoglobin A1c â‰¤ 6 % Hemoglobin, blood Male: 13.5-17.5 g/dLFemale: 12.0-16.0 g/dL Hemoglobin, plasma 1-4 mg/dL Leukocyte count and differential Leukocyte count 4,500-11,000/mm3 Segmented neutrophils 54%-62% Bands 3%-5% Eosinophils 1%-3% Basophils 0%-0.75% Lymphocytes 25%-33% Monocytes 3%-7% Mean corpuscular hemoglobin 25.4-34.6 pg/cell Mean corpuscular hemoglobin concentration 31%-36% Hb/cell Mean corpuscular volume 80-100Â Î¼m3 Partial thromboplastin time (activated) 25-40 seconds Platelet count 150,000-400,000/mm3 Prothrombin time 11-15 seconds Reticulocyte count 0.5%-1.5% of red cells Thrombin time < 2 seconds deviation from control Volume Plasma Male: 25-43 mL/kgFemale: 28-45 mL/kg Red cell Male: 20-36 mL/kgFemale: 19-31 mL/kg
 Cerebrospinal Fluid Reference Range Cell count 0-5/mm3 Chloride 118-132 mEq/L Gamma globulin 3%-12% total proteins Glucose 40-70 mg/dL Pressure 70-180 mm H2O Proteins, total < 40 mg/dL
 Sweat Reference Range Chloride 0-35 mmol/L Urine Calcium 100-300 mg/24 h Chloride Varies with intake Creatinine clearance Male: 97-137 mL/minFemale: 88-128 mL/min Estriol, total (in pregnancy) 30 wks 6-18 mg/24 h 35 wks 9-28 mg/24 h 40 wks 13-42 mg/24 h 17-Hydroxycorticosteroids Male: 3.0-10.0 mg/24 hFemale: 2.0-8.0 mg/24 h 17-Ketosteroids, total Male: 8-20 mg/24 hFemale: 6-15 mg/24 h Osmolality 50-1400 mOsmol/kg H2O Oxalate 8-40 Î¼g/mL Potassium Varies with diet Proteins, total < 150 mg/24 h Sodium Varies with diet Uric acid Varies with diet Body Mass Index (BMI) Adult: 19-25 kg/m2
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(M1.ST.14.25) An at-home recreational drug screening test kit is currently being developed. They consult you for assistance with determining an ideal cut-off point for the level of the serum marker in the test kit. This cut-off point will determine what level of serum marker is associated with a positive or negative test, with serum marker levels greater than the cut-off point indicative of a positive test and vice-versa. The cut-off level is initially set at 4 mg/uL, which is associated with a sensitivity of 92% and a specificity of 97%. How will the sensitivity and specificity of the test change if the cut-off level is raised to 6 mg/uL? Review Topic | Tested Concept

QID: 105635
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Sensitivity decreases, specificity decreases

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Sensitivity increases, specificity decreases

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Sensitivity decreases, specificity increases

58%

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Sensitivity increases, specificity increases

12%

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Sensitivity decreases, specificity may increase or decrease

2%

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(M1.ST.14.6) A 16-year-old female is seen at her outpatient primary medical doctor's office complaining of a sore throat. Further history reveals that she has no cough and physical exam is notable for tonsillar exudates. Vitals in the office reveal HR 88, RR 16, and T 102.1. Using the Centor criteria for determining likelihood of Group A beta-hemolytic strep pharyngitis, the patient has a score of 3. A review of the primary literature yields the findings in Image A. What is the specificity of the Centor criteria using a score of 3 as a cutoff value? Review Topic | Tested Concept

QID: 103968
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9/54 = 17%

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41/50 = 82%

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41/46 = 89%

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45/50 = 90%

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Not enough information has been provided

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(M1.ST.14.10) A new real time-PCR test for the hepatitis C virus is approved for medical use. The manufacturer sets the threshold number of DNA copies required to achieve a positive result such that the sensitivity is 98% and the specificity is 80%. The tested population has a hepatitis C prevalence of 0.7%. Which of the following changes in the prevalence, incidence, or threshold concentration will increase the positive predictive value of the test, if the other two values are held constant? Review Topic | Tested Concept

QID: 103972
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An increase in incidence

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An increase in prevalence

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A decrease in incidence

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A decrease in prevalence

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Lowering the threshold concentration required for a positive test.

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(M1.ST.13.4) Health officials are considering a change be made to the interpretation of the tuberculin skin test that will change the cut-off for a positive purified protein derivative (PPD) from 10 mm to 5 mm for healthcare workers. Which of the following is a true statement regarding this potential change? Review Topic | Tested Concept

QID: 103966
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This change will decrease the positive predictive value of the test

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This change will decrease the negative predictive value of the test

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This change will not change the negative predictive value of the test

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This change will not change the sensitivity of the test

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This change will increase the specificity of the test

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(M1.ST.12.1) As a public health practitioner, you are charged with choosing which blood test to use for the screening of a new infectious disease. You want to ensure that as many cases of this disease as possible are picked up by this initial screening test. Which of the following is the highest priority characteristic of this new test? Review Topic | Tested Concept

QID: 103963
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Highly sensitive test

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Highly specific test

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Low false positive rate

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High true positive rate

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Low negative predictive value

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