Summary The widespread use of haematology analysers (HA) has led to a major improvement of cellular haematology, because of quick and accurate results found in most instances. However, in several situations, spurious results are observed. Inadequate blood samples, situations induced by the anticoagulant(s) used, peculiar changes related to the pathology in the patient, and technical considerations about performances of the various HA must be considered. Spurious thrombocytopenia occurs in several circumstances related to the presence of ethylenediamine tetra‐acetic acid (EDTA) used as the anticoagulant. Mechanism of EDTA‐dependent platelet (PLT) agglutination is related to circulating (auto)antibodies directed against normally hidden epitope(s) in the glycoprotein alpha IIb/beta IIIa complex from PLT membrane exposed only in the presence of EDTA. Other spuriously low PLT counts may be related to EDTA, including PLT rosetting around white blood cells (WBC; satellitism) and PLT‐WBC aggregates, but mechanisms responsible for those latter phenomena are less well known. Spurious increase of PLT count may be related to several situations, including fragmented red blood cells, cytoplasmic fragments of nucleated cells, cryoglobulins, bacteria or fungi, and lipids. Flags generated in several of these situations alert the operator on possible abnormal findings and may identify the problem. Analysing only PLT parameters is not sufficient: in many situations the WBC differential scattergram is of crucial help for flagging. Flags generated depend on the software version on the HA used, the performance in detecting the same anomalies may differ according to which analyser is used, even those from the same manufacturer. Operators must be aware of the characteristics of their analyser and be able to recognize and circumvent anomalous results.

S U M M A R YHaematology analysers provide quick and accurate results in most situations. However, spurious results, related either to platelets (part I of this report) or to other parameters from the cell blood count (CBC) may be observed in several instances. Spuriously low white blood cell (WBC) counts may be observed because of agglutination in the presence of ethylenediamine tetra-acetic acid (EDTA). Cryoglobulins, lipids, insufficiently lysed red blood cells (RBC), erythroblasts and platelet aggregates are common situations increasing WBC counts. In most of these instances flagging and/or an abnormal WBC differential scattergram will alert the operator. Several situations lead to abnormal haemoglobin measurement or to abnormal RBC count, including lipids, agglutinins, cryoglobulins and elevated WBC counts. Mean (red) cell volume (MCV) may be also subject to spurious determination, because of agglutinins, excess of glucose or salts and technological considerations. In turn, abnormality related to one measured parameter will lead to abnormal calculated RBC indices: mean cell haemoglobin content (MCHC) is certainly the most important RBC indices to consider, as it is as important as flags generated by the haematology analysers (HA) in alerting the user to a spurious result. In many circumstances, several of the measured parameters from CBC may be altered, and the discovery of a spurious change on one parameter frequently means that the validity of other parameters should be considered. Sensitive flags now allow the identification of several spurious counts, but only the most sophisticated HA have optimal flagging and more simple HA, especially those without a WBC differential scattergram, do not possess the same sensitivity for detecting anomalous results. Reticulocytes are integrated now into the CBC in many HA, and several situations may lead to abnormal counts.

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