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pb070681 ☆ 2007-10-19 09:03 (6816 d 08:56 ago) Posting: # 1220 Views: 10,040 |
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My calibration range is 2 to 100 ng. i got backcalculated value 1.9 to 198 ng. In one subject i got concentration 199 ng. Should i repeat that sample under dilution integrity. Pramod |
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Ramesh ☆ India, 2007-10-19 09:29 (6816 d 08:29 ago) @ pb070681 Posting: # 1222 Views: 9,746 |
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Dear pramod, your calibration range is from 2 - 100 ng. any value out of the validated is not considered. if value is below the LOQ it will be considered as BLQ (below limit of quantification) and if the value is above the ULQ it will be repeated as Dilution integrity sample, but diluting the sample appropriately (to bring the concentration within the validation range) and back calculate by applying dilution factor. i hope this is helpful to you with regards, Ramesh.V — with regards, Ramesh |
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Helmut ★★★   Vienna, Austria, 2007-10-19 15:45 (6816 d 02:13 ago) @ Ramesh Posting: # 1225 Views: 8,758 |
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Dear Ramesh & Pramod! ❝ your calibration range is from 2 - 100 ng. I think that 100 ng/mL for the ULOQ is just a typo (because Pramod's back-calculated values were 1.9-198 ng/mL). So the calibration range is likely to be 2-200 ng/mL - always being based on the nominal concentrations, not the back-calulated ones. Therefore a sample with 199 ng/mL is within the CC. If it's not a typo: 2-100 ng/mL nominal, back-calculated 1.9-198 ng/mL - something with the CC went entirely wrong (LLOQ 95% of nominal, but ULOQ 198% of nominal). ❝ any value out of the validated is not considered. ... if the value is ❝ above the ULQ it will be repeated as Dilution integrity sample, but ❝ diluting the sample appropriately (to bring the concentration within ❝ the validation range) and back calculate by applying dilution ❝ factor. 100% agree! Maybe Pramod had something else in mind in his example... ULOQ 198 ng/mL, measured unknown sample 199 ng/mL. We know that any method has limited - and documented in the validation - accuracy and precision. For the acceptance of calibrators it's fine to give back-calculated concentrations of 85%-115% of nominal (80%-120% at LLOQ). If the ULOQ is 198 ng/mL a calibrator with a back-calculated concentration of 227 ng/ml (115% of the ULOQ) would be acceptable, whereas the unknown sample with 199 ng/mL is not. Of course this is counterintuitive (treating unknowns differently form calibrators). Therefore I've seen people setting the lower limit for dilution to 115% of the ULOQ. Cleary this is against the guidelines - which are not carved out of stone anyway - but if you want to avoid discussions, dilute...  — Dif-tor heh smusma 🖖🏼 Довге життя Україна! ![[image]](https://static.bebac.at/pics/Blue_and_yellow_ribbon_UA.png) Helmut Schütz ![[image]](https://static.bebac.at/img/CC by.png) The quality of responses received is directly proportional to the quality of the question asked. 🚮 Science Quotes |
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Charl ● 2007-10-22 11:09 (6813 d 06:49 ago) @ Helmut Posting: # 1232 Views: 8,679 |
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Dear HS I do agree with you (if I got your point correctly) our cc limits are not the LLOQ - ULOQ, it is 0.8xLLOQ - 1.15xULOQ. why shouldnt we work on this? After all our validation counts for accuracy. I always argue with this point, but...  regards Charl |
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Helmut ★★★ Vienna, Austria, 2007-10-22 14:46 (6813 d 03:12 ago) @ Charl Posting: # 1234 Views: 8,887 |
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Dear Charl! ❝ I do agree with you (if I got your point correctly) If I expressed myself unclearly – which are the doubtful points? ❝ our cc limits are not the LLOQ - ULOQ, it is 0.8xLLOQ - 1.15xULOQ. Hhm, we have done this for many years; but it’s a risky business… ❝ why shouldnt we work on this? Because The calibration (standard) curve should cover the expected unknown sample concentration range in addition to a calibrator sample at LLOQ. Estimation of concentration in unknown samples by extrapolation of standard curves below LLOQ or above the highest standard is not recommended. Instead, the standard curve should be redefined or samples with higher concentration should be diluted and reassayed. (my emphasis) ❝ After all our validation counts for accuracy. ❝ I always argue with this point, but... I agree with you, but…  Edit: Link corrected for FDA’s new site. [Helmut] — Dif-tor heh smusma 🖖🏼 Довге життя Україна! Helmut Schütz The quality of responses received is directly proportional to the quality of the question asked. 🚮 Science Quotes |
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Charl ● 2007-10-23 11:27 (6812 d 06:32 ago) @ Helmut Posting: # 1241 Views: 8,586 |
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Dear HS I didnt express my point correctly, the limits to accept the concentration values in the unknown samples are 0.8xLLOQ upto 1.15xULOQ not the cc limits to be so. e.g if my cc range between 1-100 ng/ml, then why not to accept the concentration of 0.8 ng/ml in the unknown samples, thus we already accept the accuracy for the LLOQ in the cc graph for the 20%. regards Charl |
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Helmut ★★★ Vienna, Austria, 2007-10-23 21:09 (6811 d 20:49 ago) @ Charl Posting: # 1242 Views: 10,116 |
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Dear Charl! ❝ I didnt express my point correctly, Oh no, you did. As I already stated, we used the same procedure for many years following exactly your arguments below. ❝ … e.g if my cc range between 1-100 ng/ml, then why not to accept the concentration of 0.8 ng/ml in the unknown samples, thus we already accept the accuracy for the LLOQ in the cc graph for the 20%. Yes, I know, but the FDA will not accept it in almost all cases, and many other regulators as well…  My recommendation to not extrapolate beyond LLOQ and ULOQ is pure pragmatism – learned the hard way – not science… — Dif-tor heh smusma 🖖🏼 Довге життя Україна! Helmut Schütz The quality of responses received is directly proportional to the quality of the question asked. 🚮 Science Quotes |
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pb070681 ☆ 2007-10-24 09:03 (6811 d 08:56 ago) @ pb070681 Posting: # 1244 Views: 8,515 |
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❝ My calibration range is 2 to 200 ng. i got backcalculated value 1.9 to 198 ng. In one subject i got concentration 199 ng (which is within nominal concentration but out of back calculated range). Should i repeat that sample under dilution integrity. (their was typo error in question) Pramod |
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Helmut ★★★ Vienna, Austria, 2007-10-26 03:32 (6809 d 14:27 ago) @ pb070681 Posting: # 1258 Views: 9,345 |
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Dear Pramad! ❝ ❝ My calibration range is 2 to 200 ng. i got backcalculated value 1.9 to 198 ng. ❝ In one subject i got concentration 199 ng (which is within nominal concentration but out of back calculated range). ❝ (their was typo error in question) OK, now I've got your point. ❝ Should i repeat that sample under dilution integrity. Since the calibration range is always based on nominal concentrations (2 – 200 ng/mL), and 199 ≤ 200 there’s no reason to dilute. — Dif-tor heh smusma 🖖🏼 Довге життя Україна! Helmut Schütz The quality of responses received is directly proportional to the quality of the question asked. 🚮 Science Quotes |
Ing. Helmut Schütz