Question

Diabetes Screening

3. Shown below are the real-life diagnostic characteristics of a particular diabetes-screening test – a fasting venous glucose measurement – from a hypothetical cross-sectional study population. Calculate the sensitivity, specificity and positive predictive value (PPV) of this screening test and estimate the prevalence of diabetes in the study population.

Table: Results of fasting venous glucose screening for diabetes.

Diabetes Screening Test	Actual diabetes status			Total
	Present		Absent
Positive (+)	True + 67	False + 38		Total + 105
Negative (-)	False – 53	True – 1842		Total – 1895
	Total diabetics 120	Total non-diabetics 1880		Total screened population 2000

Sensitivity:

Specificity:

PPV:

Prevalence of diabetes:

Selected Formulas:

Age-specific death rate = # of deaths per age stratum

Population per age stratum

Accident-specific death rate = # of deaths from accidents per age stratum

                                         Population per age stratum

Accident case-fatality rate = # of deaths from accidents per age stratum

Total # of accidents per age stratum

Mortality Rate = __# of deaths___

Population at Risk

Proportionate Mortality Ratio = # of deaths from accidents per age stratum

Total # of deaths per age stratum

Answer 1

Diabetes Screening Test	Actual diabetes status			Total
	Present		Absent
Positive (+)	True + 67 (A)	False + 38 (B)		Total + 105
Negative (-)	False – 53 (C)	True – 1842 (D)		Total – 1895
	Total diabetics 120	Total non-diabetics 1880		Total screened population 2000

Sensitivity = A/(A+C) × 100 = (67 / 120) x 100 = 55.83%

Specificity = D/(D+B) × 100 = (1842 / 1880) x 100 = 97.98%

PPV = A/(A+B) × 100 = (67 / 105) x 100 = 63.81%

Prevalence of diabetes = (Total diabetics / Total screened population) × 100 = (120 / 2000) x 100 = 6%