The Predictive Value of Indium-111 Leukocyte Scans in the Diagnosis of...
The Predictive Value of Indium-111 Leukocyte Scans in the Diagnosis of...
Total joint arthroplasty is a commonly performed procedure associated with a definite risk of postoperative infection. Moreover, diagnosing an infection after this procedure can present a challenge, as there are no preoperative tests that are consistently sensitive and specific for infection in patients who need a revision arthroplasty. Definitive diagnosis based solely on history and physical findings may prove inaccurate.
Common tests used in diagnosing infected arthroplasty include:
Scher and colleagues examined the sensitivity, specificity, positive and negative predictive values, and accuracy indium scanning in diagnosing infection after total joint or resection arthroplasty.
One hundred fifty three indium scans were performed on 143 patients for diagnostic evaluation of painful prosthesis or resection arthroplasty. Re-operation was performed on 153 patients between 1990 and 1996 and consisted of 94 total hips, 41 total knees, and 18 resection arthroplasties.
A patient diagnosed with infection had to meet 2 of the 3 following criteria:
A review of the 153 indium scans showed:
Sensitivity was defined as the ratio of true positives to true positives plus false negatives. Specificity was defined as the ratio of true negatives to true negatives plus false positives. Accuracy was defined as the total number of true positives and true negatives divided by the total number of scans performed.
All of the patients studied presented with a painful prosthesis or resection arthroplasty and underwent re-operation. Determination of infection was based on objective intraoperative criteria. Indium labels lymphocytes in addition to polymorphonuclear neutrophils (PMN) with a positive predictive value of 54%. More selective labeling may be helpful since indium scanning is not reliable for resection arthroplasty, possibly because of the inflammation that occurs.
The cost of a routine work-up (CBC, ESR, CRP, and x-rays) is $60. Bone and indium scanning costs $580, representing a 10-fold increase in cost.
Although indium scanning does not accurately predict the presence of prosthetic infection, a negative scan reliably indicates the absence of infection. Indium scanning is expensive and is not useful in determining infection for resection arthroplasty. Due to the high cost, indium scans should not be used as part of the routine evaluation of painful prosthetics following total joint arthroplasty. Prior to performing an indium scan for evaluating a painful prosthesis, laboratory tests including WBC, ESR, and CRP should be obtained. If the results are all positive or negative, there is no need for an indium scan. A frozen section will aid in definitive diagnosis of infection, and indium scans should be obtained when laboratory results are equivocal and revision is not imminent.
Made possible through an unrestricted educational grant from Smith & Nephew.
Total joint arthroplasty is a commonly performed procedure associated with a definite risk of postoperative infection. Moreover, diagnosing an infection after this procedure can present a challenge, as there are no preoperative tests that are consistently sensitive and specific for infection in patients who need a revision arthroplasty. Definitive diagnosis based solely on history and physical findings may prove inaccurate.
Common tests used in diagnosing infected arthroplasty include:
Laboratory tests (eg, white blood cells [WBC], erythrocyte sedimentation rate [ESR], and C-reactive protein [CRP])
Plain x-rays
Aspiration arthrograms
Radionuclide scanning
Technetium Tc99m
Gallium Citrate Ga 67
Indium 111-labeled leukocyte
Intraoperative frozen section
Scher and colleagues examined the sensitivity, specificity, positive and negative predictive values, and accuracy indium scanning in diagnosing infection after total joint or resection arthroplasty.
One hundred fifty three indium scans were performed on 143 patients for diagnostic evaluation of painful prosthesis or resection arthroplasty. Re-operation was performed on 153 patients between 1990 and 1996 and consisted of 94 total hips, 41 total knees, and 18 resection arthroplasties.
A patient diagnosed with infection had to meet 2 of the 3 following criteria:
Positive intraoperative culture
Acute inflammation on permanent evaluation of the specimen
Purulence within the joint during revision surgery
A review of the 153 indium scans showed:
26 infections (17% incidence)
37 positive indium scans
110 negative indium scans
6 equivocal indium scans
Sensitivity was defined as the ratio of true positives to true positives plus false negatives. Specificity was defined as the ratio of true negatives to true negatives plus false positives. Accuracy was defined as the total number of true positives and true negatives divided by the total number of scans performed.
|
|
Sensitivity | Specificity |
|
All Cases |
77% |
86% |
|
THA |
60% |
93% |
|
TKA |
0% |
78% |
|
Resection Arthroplasty |
0% |
72% |
|
|
Positive Predictive Value |
Negative Predictive Value |
|
All Cases |
54% |
95% |
|
THA |
50% |
95% |
|
TKA |
75% |
90% |
|
Resection Arthroplasty |
0% |
100% |
|
|
Accuracy |
|
All Cases |
84% |
|
THA |
89% |
|
TKA |
83% |
|
Resection Arthroplasty |
72% |
All of the patients studied presented with a painful prosthesis or resection arthroplasty and underwent re-operation. Determination of infection was based on objective intraoperative criteria. Indium labels lymphocytes in addition to polymorphonuclear neutrophils (PMN) with a positive predictive value of 54%. More selective labeling may be helpful since indium scanning is not reliable for resection arthroplasty, possibly because of the inflammation that occurs.
The cost of a routine work-up (CBC, ESR, CRP, and x-rays) is $60. Bone and indium scanning costs $580, representing a 10-fold increase in cost.
Although indium scanning does not accurately predict the presence of prosthetic infection, a negative scan reliably indicates the absence of infection. Indium scanning is expensive and is not useful in determining infection for resection arthroplasty. Due to the high cost, indium scans should not be used as part of the routine evaluation of painful prosthetics following total joint arthroplasty. Prior to performing an indium scan for evaluating a painful prosthesis, laboratory tests including WBC, ESR, and CRP should be obtained. If the results are all positive or negative, there is no need for an indium scan. A frozen section will aid in definitive diagnosis of infection, and indium scans should be obtained when laboratory results are equivocal and revision is not imminent.
Made possible through an unrestricted educational grant from Smith & Nephew.
