The added value of synovial fluid centrifugation for monosodium urate and calcium pyrophosphate crystal detection

Abstract

The aim of the study was to assess the added value of synovial fluid (SF) centrifugation for microscopic monosodium urate (MSU) and calcium pyrophosphate (CPP) crystal detection in patients with arthritis. This is a prospective observational study using SF samples from joints of patients undergoing joint arthrocentesis. Two blinded observers assessed the SF smears by polarized light microscopy for the presence of crystals before as well as after centrifugation. SF samples were collected from 98 patients with arthritis. After exclusion, 87 samples were eligible for inclusion. Of each sample, 2 smears before and after centrifugation were prepared and microscopically examined, resulting in 348 smears per observer. Observer 1 identified MSU crystals in 18.4% and CPP in 9.2% of the smears before as well as after centrifugation. No extra MSU crystal-positive smears were identified after centrifugation. However, centrifugation yielded 4 additional CPP crystal-positive smears. Observer 2 identified MSU crystals in 15.5% and CPP crystals in 6.3% of the smears before as well as after centrifugation. Centrifugation yielded 2 additional MSU crystal-positive smears and 4 CPP crystal-positive smears. Monosodium urate crystals were well recognized without centrifugation. Centrifugation of SF had limited additional value for increasing the amount of MSU-positive smears. However, CPP crystals were identified in a higher number of smears after centrifugation than before. Therefore, centrifugation may be of additional value in selected patients with suspected calcium pyrophosphate deposition disease and to a lesser extent for gout.

Clinical implications of synovial fluid specimen handling for crystal associated arthritides: A systematic review

“…Detailed study results are provided in the tables and major findings are given below. Seven studies used compensated polarized microscopy 19‐25 . Two studies utilized only polarized microscopy 26,27 .…”

“…Centrifugation and cytocentrifugation were the 2 techniques assessed. One study compared regular smears with centrifugation in which the latter allowed for identification of an additional 7% MSU cases and 20%‐27% (2 observers) CPP cases 25 . One study compared regular smears with cytocentrifugation, in low inflammation SF, and identified 100% MSU crystals compared to 71% with regular smears 32 .…”

“…Centrifugation was assessed by 1 study and enabled detection of an additional, approximately, 25% SF specimens with CPP crystals 25 . It also modestly enhanced MSU detection.…”

“…Seven studies used compensated polarized microscopy. [19][20][21][22][23][24][25] Two studies utilized only polarized microscopy. 26,27 In 6 studies, the method of polarized microscopy could not be determined.…”

Laboratory testing of extravascular body fluids: National recommendations on behalf of the Croatian Society of Medical Biochemistry and Laboratory Medicine. Part II – Synovial fluid

“…Nevertheless, cytocentrifugation has several limitations: a) it requires more time to prepare the slide; b) it requires special equipment (cytocentrifuge); and c) in the presence of a large number of cells, the identification of crystals is more difficult. Alternatively, in the absence of a cytocentrifuge, slides for microscopic crystal analysis can be prepared using a conventional centrifuge, centrifuging samples for 10 minutes at 700 rpm ( 8 , 46 ).…”