Infection is a leading indication for revision
arthroplasty. Established criteria used to diagnose prosthetic joint infection
(PJI) include a range of laboratory tests. Leucocyte esterase (LE)
is widely used on a colorimetric reagent strip for the diagnosis
of urinary tract infections. This inexpensive test may be used for
the diagnosis or exclusion of PJI. Aspirates from 30 total hip arthroplasties
(THAs) and 79 knee arthroplasties (KA) were analysed for LE activity. Semi-quantitative
reagent strip readings of 15, 70, 125 and 500 white blood cells
(WBC) were validated against a manual synovial white cell count
(WCC). A receiver operating characteristic (ROC) curve was constructed
to determine the optimal cut-off point for the semi-quantitative
results. Based on established criteria, six THAs and 15 KAs were
classified as infected. The optimal cut-off point for the diagnosis
of PJI was 97 WBC. The closest semi-quantitative reading for a positive
result was 125 WBC, achieving a sensitivity of 81% and a specificity
of 93%. The positive and negative predictive values of the LE test
strip were 74% and 95% respectively. The LE reagent strip had a high specificity and negative predictive
value. A negative result may exclude PJI and negate the need for
further diagnostic tests. Cite this article:
Cut-off values with highest sensitivity and specificity
for the synovial fluid white cell and differential count will facilitate
the accurate diagnosis of infection in total knee (TKR) and total
hip replacement (THR). All patients undergoing revision TKR or THR
for suspected prosthetic joint infection between 2009 and 2011 at
two hospitals were identified. A total of 75 patients were included
with a mean age of 70.3 years (38 to 89). Synovial fluid was aspirated
pre-operatively and peri-prosthetic tissue samples were taken intra-operatively
for histological and microbiological examination. Receiver operating characteristic (ROC) plots were constructed
for white cell and differential counts in aspirated fluid. The optimal
cut-off for TKR and THR was 1590 white cells/µl and 65% neutrophilia.
The white cell count cut-off value identified for THR was notably
lower than previously quoted in the literature. A cut-off value
for white cell count in synovial aspirate in suspected prosthetic
joint infection of between 1100 and 1700 white cells/µl is likely
to be applicable to both THR and TKR. Cite this article:
