Negative findings on LE cell testing exclude a diagnosis of systemic lupus erythematosus (SLE).
The presence of LE cells indicates lupus.
A smear is considered positive when 10 or more characteristic LE cells are seen during a 15-minute search, associated with the presence of extracellular, amorphous, nuclear masses.
A lupus erythematosus (LE) cell test is considered positive when approximately 2%-30% of the cells seen on the slide in the neutrophil count are LE cells. The integrity of the test depends on the technical skill and observation of the test performer.
Collection and Panels
Lupus erythematosus (LE) cell testing is performed using any of the following:
Heparinized bone marrow
Heparinized venous blood
Oxalated venous blood
Defibrinated venous blood
Clotted venous blood
LE factor and donor cells 
Obtaining bone marrow is usually distressing for the patient; therefore, the buffy coat from venous blood is an adequate substitute. If the equipment for buffy coat is unavailable, an untreated venous blood sample is left to clot (from 20-120 minutes) and the plasma removed. The residual clot is passed through a wire mesh and centrifuged for 5 minutes to obtain a buffy coat. This buffy coat is then smeared on glass slides to search for LE cells. 
The test may be performed by mixing the patient's plasma, serum, or serous effusions as a source of LE factor with bone marrow from a donor subject.
The lupus erythematosus (LE) cell was first described by Hargraves, Richmond, and Morton in I948. LE cells were observed in the bone marrow of patients with lupus. 
The LE cell reaction is positive in 50%-75% of individuals with acute disseminated lupus. Positive reactions are also seen in rheumatoid arthritis, chronic hepatitis (lupoid), scleroderma, dermatomyositis, polyarteritis nodosa, acquired hemolytic anemia, and Hodgkin disease. It may also be positive in persons taking phenylbutazone and hydralazine.
The ideal temperature to perform this test is 22°C, and the process may be hastened by incubation at 37°C.
LE cell testing is no longer used to diagnose lupus erythematosus; ANA is the criterion standard.