1. Marta José, Instituto Grifols S.A., Barcelona, SPAIN
EXPERIENCE WITH IN-HOUSE ASSAY: VALIDATION OF AN IN-HOUSE NAT ASSAY FOR THE DETECTION OF DIFFERENT GENOTYPES OF vB19
Marta José, Instituto Grifols S.A., Barcelona, SPAIN
SoGAT Standardisation of Parvovirus B19 Genotypes, March 2007

2. IN-HOUSE vB19 METHOD DESIGN
Automatic DNA extraction using the BioRobot 9604 (QIAGEN).
Subsequent amplification by PCR of a conserved sequence of VP1 capsid structural protein region.
Detection by means of a specific capture probe in a liquid medium and colorimetric reaction (ELISA-DIG Detection, Roche).
The internal control (from the extraction) is a plasmid which is amplified with the same primers as vB19 without competition, and detected with a different probe.
SoGAT Standardisation of Parvovirus B19 Genotypes, March 2007

3. IN-HOUSE vB19 METHOD DESIGN and VALIDATION
The method is designed to work in the exponential phase of the PCR reaction in order to use the same procedure as qualitative or quantitative assays.
The method is validated according to current guidelines for the following parameters: detection limit, quantitation limit, linearity, range, accuracy, precision, specificity and robustness.
SoGAT Standardisation of Parvovirus B19 Genotypes, March 2007

4. IN-HOUSE vB19 METHOD VALIDATION: DETECTION LIMIT
This detection limit is applicable when the method is used to give qualitative results.
The detection limit at 95 % and 50 % was established by Probit test using the WHO IS for vB19 DNA NAT assays code 99/800.
WHO IS 99/800
Dilution
1/101.75
1/102
1/102.25
1/102.5
1/102.75
Titre
IU/ml
17783
10000
5623
3162
1778
Positives vs replicates
Total
24/24
23/24
20/24
15/24
9/24 %
100
95.8
83.3
62.5
37.5
95 % Detection limit
9.2 x 103 IU/ml
(CI 95 %: 6.6 X 103 – 1.8 X 104 IU/ml)
50 % Detection limit
2.4 x 103 IU/ml
(CI 95 %: 1.6 X 103 – 3.0 X 103 IU/ml)
SoGAT Standardisation of Parvovirus B19 Genotypes, March 2007

5. IN-HOUSE vB19 METHOD VALIDATION: QUANTITATION LIMIT
This quantitation limit (QL) is applicable when the method is used to give quantitative results.
To calculate the quantitation limit, different dilutions of WHO IS, near the detection limit were assayed. A regression test between the titre (IU/ml) and the OD mean of each concentration was applied.
Titre (IU/ml)
OD Mean*
562.34
0.104
1000
0.136
1778.3
0.215
REGRESSION TEST
Slope
9 x 10-5
Standard error of the interception (δ) R2
0.9941
QL (IU/ml)
941.64
(2.97 log10)
*Mean of 3 independent assays in triplicate
SoGAT Standardisation of Parvovirus B19 Genotypes, March 2007

6. IN-HOUSE vB19 METHOD VALIDATION: QUANTITATIVE METHOD
Linearity: The method is linear in the range studied, between 1.8x103 and 105 IU/ml ( log10 IU/ml) with a coefficient of regression 0.95 and a coefficient of determination 0.91 .
Accuracy: The method shows a correct accuracy in the interval from 3.25 to 4.75 log10 IU/ml with a recovery within the interval 100 ± 10% for each concentration.
Precision: In the same interval the method shows a correct precision, with a coefficient of variation of 10%, for both repeatability and intermediate precision studies.
Range: The method is accurate and precise in the concentration range between 3.25 and 4.75 log10 IU/ml.
SoGAT Standardisation of Parvovirus B19 Genotypes, March 2007

7. IN-HOUSE vB19 METHOD VALIDATION: GENERAL PARAMETERS
ROBUSTNESS
Cross-contamination: 20 samples of negative plasma spiked with vB19 DNA at approximate final concentration of 106 IU/ml, mixed alternately with the same samples without spiking, were tested. The results showed that the measures taken to prevent cross-contamination are efficacious.
The method shows no operating differences neither with the extraction kit batch nor with the thermocycler employed.
SPECIFICITY I
No cross-reactivity was observed with the presence of other blood borne viruses (HCV, HIV-1, HBV, HAV, GBV-C).
No interference was detected by the presence of these viruses.
SoGAT Standardisation of Parvovirus B19 Genotypes, March 2007

8. IN-HOUSE vB19 METHOD VALIDATION: SPECIFICITY II.- Genotype 2 detection
A6 virus DNA sample (genotype 2) from European Pharmacopoeia panel was analysed at titres of 104, 105 and 106 IU/ml and detected as positive using the qualitative method with a 95 % detection limit of 9.2 x 103 IU/ml.
Two samples of the same donor analysed during the validation of the method were identified as genotype 2.
QUANTITATION RESULTS
Sample
GRIFOLS’ method
Lab 1
Lab 2
Sample A
1.90x107 IU/ml
1.14x107 IU/ml NT
Sample B
3.71x109 IU/ml
>5.1x108 IU/ml
≈1x1010 IU/ml
N.T.: Not Tested
SoGAT Standardisation of Parvovirus B19 Genotypes, March 2007

9. IN-HOUSE vB19 METHOD VALIDATION: SPECIFICITY III
IN-HOUSE vB19 METHOD VALIDATION: SPECIFICITY III.- Genotypes 3 and 1 detection
Genotype 3
A vB19 genotype 3 sample with a previous titre established in 105 IU/ml was analysed at titres between 104 and IU/ml and found positive with our qualitative method.
The titre established by our quantitative method was also of 105 IU/ml.
Genotype 1
The vB19 genotype 1 detection was demonstrated during the method validation using different samples (IS, NIBSC, working reagents and in-house calibrated controls).
SoGAT Standardisation of Parvovirus B19 Genotypes, March 2007

10. IN-HOUSE vB19 METHOD VALIDATION: CONCLUSIONS I
Qualitative method:
The detection limit at 95 % has been established in 9.2 x 103 IU/ml.
Quantitative method:
The quantitation limit has been established in IU/ml.
The method is linear in the range studied, between 3.25 and 5 log10 IU/ml.
The method shows correct accuracy and precision in the concentration range between 3.25 and 4.75 log10 IU/ml.
Qualitative and quantitative method:
The measures taken to prevent cross-contamination are efficacious.
The method shows no operating differences neither with the extraction kit batch nor with the thermocycler employed.
Neither cross-reactivity nor interference was observed with the presence of other blood borne viruses (HCV, HIV-1, HBV, HAV, GBV-C).
SoGAT Standardisation of Parvovirus B19 Genotypes, March 2007

11. IN-HOUSE vB19 METHOD VALIDATION: CONCLUSIONS II
Qualitative and quantitative method:
The method detects and quantitates samples of genotypes 1, 2 and 3 of vB19 with approximately the same efficacy.
We developed and validated an in-house PCR method for detection and/or quantitation of vB19 DNA that could detect samples from the three described genotypes.
SoGAT Standardisation of Parvovirus B19 Genotypes, March 2007

12. ACKNOWLEDGEMENTS INSTITUTO GRIFOLS: Araceli Maya Mireia Prat
Dr. Rodrigo Gajardo
Dr. Juan I. Jorquera
NATIONAL BLOOD SERVICE
CAMBRIDGE UNIVERSITY, UK:
Dr. Daniel Candotti
Dr. Jean Pierre Allain
BIOMAT (GRIFOLS):
Margarita Estrada
Dr. Dolors Xairó
SANQUIN, NETHERLANDS:
Dr. Marco Koppelman
SoGAT Standardisation of Parvovirus B19 Genotypes, March 2007