Question

IMG 2585.HEIC A study was conducted to evaluate the utility of using the red cell protoporphyrin concentration as a measure of iron deficiency (red cell protoporphyrin is elevated in the case of iron deficiency). A group of volunteers nad bone marrow biopsies cell protoporphyrin concentrations. The results are below: as a gold standard measure of iron deficiency and these results were compared to the red Bone marrow iron: Not iron Iron deficient Red cell protoporphyrin < 50 ug/dL 50-149 ug/dL 150-249 ug/dL 250-349 Hg/dL 2350 ug/dL deficient 15 1 132 42 23 26 5 17 14 Calculate the sensitivity, specificity, and positive predictive value of the red cell protoporphyrin at a cutoff value of 2150 ug/dL, where high values would be considered as screening positive for iron deficiency 5, 4. Sensitivity: e A. 17% TP B. 83% 31 5. Specificity: T C. 57% 132 D. 65% 43 31 E) 43% 6. Positive Predictive Value: 57 7. If you wanted to maximize the specificity of the test, irrespective of sensitivity, which cutoff value would you use? A. 250 Hg/dL B 2150 g/dL C 2250 g/d D. 2350 Hg/dL

Answer 1

A study was conducted to evaluate the utility of using the red cell protoporphyrin concentration as a measure of Iron deficiency. A group of volunteers had bone marrow biopsies as a gold standard measure of iron deficiency and these results were compared to the red cell protoporphyrin concentration. Calculate the sensitivity, specificity, and positive predictive value of the red cell protoporphyrin at a cut-off value of greater than or equal to 150mug/dl. where high values would be considered as a screen positive for iron deficiency?

A. Sensitivity = True Positive (TP) / True positive(TP) + False Negative(FN)

True Positive (TP) =100	False Positive (FP) = 178
False Negative (FN) =178	True Negative(TN) = 100

Sensitivity : 0.360

B. Specificity = True Negative/ True Negative + False Positive

Specificity : 0.360

C. Positive Predictive Value: True Positive/ True Positive + False Positive

Positive predictive value = 0.359

If you wanted to maximize the specificity of test irrespective of sensitivity which cut off value would you use?

A. $\geq$ 50mug/dl