Platelet count

Hematology analyzer design and sample technique for optimized platelet count in feline samples

A complete blood count (CBC) can be obtained either by manual microscopy or through an automated procedure using a hematology analyzer. Platelets (PLTs) are the most time-consuming blood cells to count manually, as they cannot be counted together with the red blood cells (RBCs) and white blood cells (WBCs). Using a Bürker chamber for manual microscopy, PLTs instead need to be counted separately.

However, manual microscopy is a labor-intensive method, and an automated system can be a more efficient solution. Nevertheless, PLTs are difficult to count also for an automated analyzer. Not only do PLTs vary largely between different species, they also tend to aggregate to PLT clumps. PLTs in cat samples are especially prone to aggregation and therefore constitute the biggest challenge for the analyzer. PLT clumps formed in cat samples are of various size and can be large enough to pass through the aperture and counted as a WBC, resulting in pseudo-thrombocytopenia and in most cases falsely elevated lymphocytes. Moreover, many hematology analyzers today do not report low platelet results, which can be critical for patients going through, for example, surgery, chemotherapy or just for monitoring the effectiveness of certain treatments.

Exigo™ H400 design ensures accurate PLT count in cats

Exigo H400 is designed to minimize inaccurate results due to PLT aggregation. For example, the smaller aperture of only 60 µm, compared with 80 µm of the analyzers for human use, increases the sensitivity for the smaller cells, improving repeatability and accuracy of the RBC and PLT counts. In addition, the analyzer features optimized software adaptations such as coincidence compensation factor algorithms, extra sample mixing times and extra lysing time for cat samples. These software optimizations allow getting results for critically low platelet counts, less than 15 × 109/L, to monitor patients with diseases affecting the platelets.

The reagent composition is also of utmost importance for reliable results. Boule’s cell count processes have been tested and optimized for decades, allowing robust and reliable analysis results. The use of the reagents designed by Boule Diagnostics for the specific instrument ensures analytical quality and performance of the hematology system.

In a clinical study at University veterinary hospital Strömsholm in Sweden, good correlation was obtained between Exigo H400 and a reference analyzer for cat PLTs (Fig 1).



Figure 1. Passing-Bablok regression graphs (left) and Bland-Altman difference plots (right) PLT, showing agreement between the Sysmex XT-2000iV (reference) and the Exigo H400 (test) hematology analyzer for cat PLT count. In regression plots, the gray line is the line of identity (x=y) and the red line is the line of best fit. In difference plots, the gray line is the line of identity, the dark blue line is the bias (mean difference between measurements), and the dashed blue lines are the 95% limits of agreement.

Exigo H400 MPA module facilitates cat sample analysis

Exigo H400 is equipped with a micropipette adaptor (MPA) designed to simplify capillary blood sample collection and analysis. The MPA functionality is especially suited for cat samples with suspected PLT aggregates. By running the cat whole blood sample using the MPA sampling method, the largest PLT aggregates are prevented from passing through. When the blood is flushed using diluent to the mixing cup, the sample is mixed with reagent, allowing potential smaller aggregates to be dissolved. The greater surface area to volume of the EDTA-coated microcapillaries, compared with EDTA test tubes, is also a factor that can contribute to less aggregation of the PLTs.

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