| Date | November 2018 | Marks available | 6 | Reference code | 18N.3.HL.TZ0.12 |
| Level | Higher level | Paper | Paper 3 | Time zone | TZ0 / no time zone |
| Command term | Explain | Question number | 12 | Adapted from | N/A |
Question
Explain two or more laboratory tests that can be used to detect the presence of specific pathogens in patients with an infectious disease.
Markscheme
a. blood/urine cultures to diagnose bacterial infections ✔
ELISA:
b. «ELISA» uses antibodies specific to pathogen antigen ✔
c. the antibodies are linked to an enzyme ✔
d. after binding of the antibody enzyme complex samples are washed to remove unbound complex ✔
e. is added for the enzyme which changes colour «if they join with an antigen» ✔
MICROARRAY:
f. test for specific mRNA sequences «using a microtiter plate» ✔
g. reverse transcriptase used to make cDNA from mRNA, linked with fluorescent dye ✔
h. «laser» light detects when cDNA and DNA hybridize which confirms presence of protein ✔
PCR:
i. detection of genetic material from the pathogen is obtained using a PCR «by using primers based on pathogen sequences» ✔
j. if DNA/RNA is amplified «more than control» then infection is confirmed ✔
k. problems of false positive or false negative «in test result interpretation» ✔
