Evaluation and performance of the Coulter STKS

The Coulter STKS is a fully automated haematology analyser which quantitatively measures and computes haematological quantities including a full "five-part" differential. The aim of this study was to evaluate whether the Coulter STKS can be used for screening purposes in a non-academic clinic. Results from the haemocytometry part of the apparatus correlated very well with those from the Coulter S Plus IV. Reasonable to good correlations were obtained with the standard manual 100-cell differential for neutrophils, lymphocytes, monocytes and eosinophils. Significantly higher percentages of monocytes were found by microscopic observation than by the STKS. Samples from 1080 patients were analysed on the STKS, and manual differentials were also performed. After revision of discrepancies and with the exclusion of neonatal samples, a good numerical agreement for the "five-part" differential was obtained. The STKS gave 1.8% false negatives, and both diagnostic sensitivity (96.3%) and specificity (83.3%) were high. A false negative rate of 1.9% was found for the indication left-shift, with a predictive value of a negative test of 97.4%. The predictive value of a positive test, however, was only 40.3%. An authorization procedure was implemented to reduce false negative samples. The routine laboratory work load for our differentials can be reduced by up to 70%. The Coulter STKS gave a high number of suspect flags for neonatal samples (75%) and is therefore not suitable for screening neonates.