Abstract
Some thromboplastin manufacturers are currently supplying the instrument- specific international sensitivity index (ISI) values of their reagents, allowing clinical laboratories to calculate instrument-specific international normalized ratio (INR) values on plasma samples from patients receiving coumarin therapy. However, the assumption that systematic interinstrument variability in the INR would be eliminated if manufacturer-determined ISI values were used remains unsubstantiated. This assumption was evaluated by comparing INR values obtained on one instrument that measures a mechanical endpoint (fibrometer) with one that measures a photo-optical endpoint (MLA- 700). Three thromboplastin reagents with instrument-specific ISI values supplied by the manufacturer (ISI range, 1.23-2.79) were used. For two of three reagents, the fibrometer INR values were significantly higher than the MLA-700 INR values (P < .01). Analysis of log prothrombin time ratio plots showed that this systematic variability was caused by inaccurate manufacturer ISI values. Of clinical significance is that the inaccurate ISI values produced a high number of discordant INR values between these two instruments (> 47% of plasma samples had one INR value within and one out of the recommended therapeutic range). The implication of these findings for laboratory monitoring of oral anticoagulation is discussed.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 128-133 |
| Number of pages | 6 |
| Journal | American Journal of Clinical Pathology |
| Volume | 102 |
| Issue number | 1 |
| State | Published - 1994 |
| Externally published | Yes |
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Keywords
- International normalized ratio
- International sensitivity index
- Oral anticoagulation
- Prothrombin time
ASJC Scopus subject areas
- Pathology and Forensic Medicine
Cite this
The reliability of manufacturer-determined, instrument-specific international sensitivity index values for calculating the international normalized ratio. / Cunningham, M. T.; Johnson, G. F.; Pennell, B. J.; Olson, John D.
In: American Journal of Clinical Pathology, Vol. 102, No. 1, 1994, p. 128-133.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - The reliability of manufacturer-determined, instrument-specific international sensitivity index values for calculating the international normalized ratio
AU - Cunningham, M. T.
AU - Johnson, G. F.
AU - Pennell, B. J.
AU - Olson, John D
PY - 1994
Y1 - 1994
N2 - Some thromboplastin manufacturers are currently supplying the instrument- specific international sensitivity index (ISI) values of their reagents, allowing clinical laboratories to calculate instrument-specific international normalized ratio (INR) values on plasma samples from patients receiving coumarin therapy. However, the assumption that systematic interinstrument variability in the INR would be eliminated if manufacturer-determined ISI values were used remains unsubstantiated. This assumption was evaluated by comparing INR values obtained on one instrument that measures a mechanical endpoint (fibrometer) with one that measures a photo-optical endpoint (MLA- 700). Three thromboplastin reagents with instrument-specific ISI values supplied by the manufacturer (ISI range, 1.23-2.79) were used. For two of three reagents, the fibrometer INR values were significantly higher than the MLA-700 INR values (P < .01). Analysis of log prothrombin time ratio plots showed that this systematic variability was caused by inaccurate manufacturer ISI values. Of clinical significance is that the inaccurate ISI values produced a high number of discordant INR values between these two instruments (> 47% of plasma samples had one INR value within and one out of the recommended therapeutic range). The implication of these findings for laboratory monitoring of oral anticoagulation is discussed.
AB - Some thromboplastin manufacturers are currently supplying the instrument- specific international sensitivity index (ISI) values of their reagents, allowing clinical laboratories to calculate instrument-specific international normalized ratio (INR) values on plasma samples from patients receiving coumarin therapy. However, the assumption that systematic interinstrument variability in the INR would be eliminated if manufacturer-determined ISI values were used remains unsubstantiated. This assumption was evaluated by comparing INR values obtained on one instrument that measures a mechanical endpoint (fibrometer) with one that measures a photo-optical endpoint (MLA- 700). Three thromboplastin reagents with instrument-specific ISI values supplied by the manufacturer (ISI range, 1.23-2.79) were used. For two of three reagents, the fibrometer INR values were significantly higher than the MLA-700 INR values (P < .01). Analysis of log prothrombin time ratio plots showed that this systematic variability was caused by inaccurate manufacturer ISI values. Of clinical significance is that the inaccurate ISI values produced a high number of discordant INR values between these two instruments (> 47% of plasma samples had one INR value within and one out of the recommended therapeutic range). The implication of these findings for laboratory monitoring of oral anticoagulation is discussed.
KW - International normalized ratio
KW - International sensitivity index
KW - Oral anticoagulation
KW - Prothrombin time
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UR - http://www.scopus.com/inward/citedby.url?scp=0028043328&partnerID=8YFLogxK
M3 - Article
VL - 102
SP - 128
EP - 133
JO - American Journal of Clinical Pathology
JF - American Journal of Clinical Pathology
SN - 0002-9173
IS - 1
ER -