Question

1. A new tumour marker for ovarian cancer is evaluated for sensitivity by testing serum samples from patients who have been diagnosed by staging biopsy as having malignant or benign lesions.

The following results were obtained:

Number of malignant patients who are positive for ovarian cancer = 21 out of 24 Number of benign patients who are negative for ovarian cancer = 61 out of 62

a. What is the sensitivity of the new ovarian cancer test?

b. What is the specificity of benign patients for the ovarian cancer? c. How would you interpret these results to a layman?

2. (a) Under what circumstances do we perform direct and indirect coombs test.? (b) Write the procedure for performing direct and indirect coombs test

3. A sample from a 65-year-old male arrived in the laboratory at 9 am from a well-man clinic. The potassium is 8.5 mmol/L (range=3.5 – 5.0 mmol/l) which is dangerously high. The sample is repeated and the same result is obtained. All other laboratory checks have been carried out and the result is analytically valid. The result is telephoned to the Medical Officer who reveals that the sample was taken at 4 pm the previous day by the nurse.

(a) What is the most likely cause of the high result?

(b) What would your recommended course of action be?

4. (a) State five properties of an ideal fixative

(b) State five differences between gram positive and gram negative bacteria.

Answer 1

Ans 1: a) The sensitivity of test is 87.5%

b) According to me specificity of benighn patient is appx.98%

Ans 2: a) It is to determine the condition of the patient whether that patient is1. anemic(Direct coombs test: detects antibodies tht are stuck on the surface of RBC) or 2) the patient is showing reactions to blood transfusion(Indirect Coobs test : Detects freely floating antibodies)

b) Procedure: Coombs test: Tajke blood sample in isotonic saline ----> wash three times with normal saline to remove the traces of serum-----> Add anti-human serum----> centrifuge for 1 minute at 1500 RPM----> Examine microscopically for agglutination

Indirect coombs test: Take recipient s serum and add donor s blood sample to the tube with serum---->add antihuman serum----> Observe for agglutination of RBC bcz of Human Igs attachment to RBCs

Ans3: a) It may be due to the delayed processing which results into the exhaustion of available glucose to generate ATP. which is concerned to sodium pottasium pumps, and failure of pump results in leakage of pottasium and result in false elevation of pottasium in blood

b) Recommended course of action is to take the blood sample fresh and check for pottasium

Ans;;4a) Properties of Ideal fixative:It prevents tissue volume

2: It helps in fixing all components and preserves tissue in natural state

3: It helps in the enhancement of staining done to the tissue

4: IT should not be very expensive , toxic, allergic for users

5:It prevents autolysis

4b: Difference between Gram positive and gram negative bacteria

Gram Positive	Gram negative
stains purple after Gram s staining	Stains red or pink after gram s staining
cell wall have thick layers of peptiidoglycan	cell wall have thin layer of peptidoglycan
outer membrane lack lipopolysaccharide component	outer membrane contains the lipopolysaccharide component
Cell wall contains teichoic acid	Cell wall do not contain teichoic acid
Secrete toxins called as exotoxins	It can secrete both endotoxins and exotoxins
eg:Streptococcus pneumoniae	eg: E.coli