Multicenter evaluation of the 3% paraformaldehyde method for white cell counting in leukocyte-reduced red blood cells. BEST (Biomedical Excellence for Safer Transfusion) Working Party of the International Society of Blood Transfusion.
OBJECTIVE
The 3% paraformaldehyde (PFA) method is a simple technique for counting residual white blood cells (WBC) in leukocyte-depleted red blood cells (RBC). Preliminary data suggested that its sensitivity is at least equal to PCR and flow cytometry. We report the results of a multicenter study conducted by the BEST Working Party to determine precision and accuracy of the 3% PFA method.


METHODS
In the 7 participating laboratories, 5 sets of samples containing nominal concentrations of 200, 100, 50, and 10 WBC/ml were prepared by diluting whole blood into 'WBC-free' RBC. Ten milliliters of each sample were processed using the 3% PFA method, which is based on erythrocyte lysis and WBC concentration into 5% of the original sample volume; a Nageotte chamber is used to count concentrated WBC.


RESULTS
The precision of the technique varied according to the nominal concentration, ranging from a CV of 12% at 200 WBC/ml to 57% at 10 WBC/ml. The technique measured fewer than the nominal WBC concentrations (mean of all laboratories, -12.4%); underestimation was probably due to cell loss during sample manipulation. Overall accuracy was however acceptable, because statistical considerations establish that the actual WBC concentration would unlikely exceed 2 times the estimated count.


CONCLUSIONS
The 3% PFA method is suitable for the enumeration of residual WBC at concentrations > or = 50/ml. It represents a useful tool for evaluation of high performance filters by reference laboratories.
Prati
D
D
Centro Trasfusionale e di Immunologia dei Trapianti, IRCCS Ospedale Maggiore, Milano, Italy.
Brandwein
H
H
Capelli
C
C
Dzik
W H
WH
Masse
M
M
Myllylä
G
G
Stromberg
R R
RR
Takahashi
T
T
Vyas
G N
GN
Wenz
B
B
D002469:Cell Separation; D004906:Erythrocyte Count; D005069:Evaluation Studies as Topic; D005404:Fixatives; D005557:Formaldehyde; D006801:Humans; D007958:Leukocyte Count / Q000295:instrumentation / Q000379:methods*; D008853:Microscopy; D015588:Observer Variation; D011108:Polymers; D012680:Sensitivity and Specificity; D014462:Ultrafiltration
D005404:Fixatives; D011108:Polymers; D005557:Formaldehyde; C003043:paraform