Is this test useful: Practical - HIV
|
|
With disease
|
Without disease
|
| test positive
|
152
|
20
|
| test negative
|
8
|
980
|
- Q2
- Sensitivity=[math]\displaystyle{ \frac{152}{160} = 0.95 }[/math]
- Specificity=[math]\displaystyle{ \frac{980}{1000} = 0.98 }[/math]
a)
|
|
With disease
|
Without disease
|
sum
|
| test positive
|
38
|
1999.2
|
2037.2
|
| test negative
|
2
|
97960.8
|
97962.8
|
| sum
|
40
|
99,960
|
100,000
|
- Positive predictive value=[math]\displaystyle{ \frac{38}{38+1999.2}=0.0187 }[/math]
- Negative predictive value=[math]\displaystyle{ \frac{97960.8}{2+97960.8}=0.999 }[/math]
b)
|
|
With disease
|
Without disease
|
| test positive
|
316.35
|
13.34
|
| test negative
|
16.65
|
653.66
|
| sum
|
333
|
667
|
- Positive predictive value=[math]\displaystyle{ \frac{316.35}{316.35+13.34}=0.959 }[/math]
- Negative predictive value=[math]\displaystyle{ \frac{653.66}{16.65+653.66}=0.975 }[/math]
To have high sensitivity is more important, because testing blood donor is a screening test and false-negative has to be excluded as much as possible.
We need to calculate PPV and show the director how much false-positive donors arise.
We should advise the director that donors should be informed to proceed to an additional confirmation test, not just be informed simple positive result.
Is this test useful: COVID-19 Practical
|
|
RT-PCR Positive
|
RT-PCR Negative
|
| IgG/M RDT Positive
|
91
|
6
|
| IgG/M RDT Negative
|
7
|
174
|
| sum
|
98
|
180
|
- Sensitivity=[math]\displaystyle{ \frac{91}{98} = 92.9\% }[/math]
- Specificity=[math]\displaystyle{ \frac{174}{180} = 96.7\% }[/math]
- Question 2
- We should know each figures of positive results of IgG and IgM, because IgG only appears during convalescent period after acute infection and is of little use for bedside diagnosis.
- As well as we still don't know well when IgM appears in blood during acute phase of COVID, which means even IgM RDT may be of little use for bedside diagnosis.
- One more thing we have to be careful is that RT-PCR would show positive for a long period after infection like 2-4 weeks, thus even though RDT shows good sensitivity and specificity compared to RT-PCR collected from asymptomatic persons, RDT results do not necessarily reflect acute phase status.
- Question 3
- (a) No
- Given the prevalence of RT-PCR positive results count 50% of asymptomatic HCWs, why antibody RDT might help to lift self-isolation of mildly symptomatic HCWs .... ? Icouldn't understand what this question wanted to ask.
- (b) No
- Because IgM/G RDT positive results cannot tell whether the patients are in acute or convalescent or post-infection status.
- (c) Partially yes
- If combination of negative IgM and positive IgG truly meant post-infection and guaranteed definite immunity, the RDT could be used for the purpose.
- Question 4
- We still could not have established definite gold or reference standard against acute infection of COVID, so I guess the only possible reference standard against new RT-PCR would be existing RT-PCR.
