Improving the Diagnosis of Platelet Storage Pool Deficiencies (SPD) Screening with the PFA-100® and New Experimental Collagen Cartridges.

Storage pool deficiencies (SPD) are clinically silent or present with mild to moderate bleeding symptoms, and their diagnosis remains often elusive to conventional laboratory tests. The PFA-100® has proven to be a very sensitive “in vitro” bleeding test for the most frequent alterations of primary hemostasis (aspirin like disorders and type 1 VWD). However, its ability to detect SPD has not been established. Moreover, the pattern of abnormalities in closure times (CT) in SPD is indistinguishable form that observed after aspirin (ASA) intake (prolonged COL-EPI and normal COL-ADP). We have explored the difficulties in the laboratory detection of patients with SPD and the possibility of establishing new parameters that could facilitate a differential diagnosis between SPD and aspirin-like defects.

We performed studies in a group of 12 patients with a previously established diagnose of SPD and also in a concurrent group of healthy donors who agreed to be tested before and after ASA treatment (100 mg/day for 7 days). We used the PFA-100® with conventional COL-EPI and COL-ADP cartridges, and the new experimentally developed cartridges containing collagen alone (COL) or collagen + arachidonic acid (COL-AA). Parallel studies with standard aggregometric procedures were performed in all cases. Our in lab range of normal values was used to define alterations in closure times with the PFA-100® or abnormalities in aggregometry responses to the battery of agonists tested.

Despite the confirmed diagnosis, standard aggregometric procedures only revealed objective alterations in 4 patients with SPD (33%). Aggregometry always detected the inhibitory action of ASA on arachidonic acid induced responses. Average closure times with the PFA-100® using COL-EPI cartridges were prolonged in patients with SPD (146 ± 16 vs. 113 ± 24 in controls; p<0.01, mean ± SD), but still within limits of normal range in 50% of the SPD patients when analyzed individually. All the SPD patients showed abnormally prolonged closure times with the experimental COL cartridges (257 ± 42 vs. 161 ± 62 s, p<0.01). Treatment with ASA caused prolongations in the closure times with COL-Epi (>224 s) or COL (>300 s) cartridges in the healthy population. Closure times with COL-AA cartridges returned to the normal range in all the patients with SPD, but remained prolonged in the healthy donor group that had been subjected to ASA treatment.

Studies with conventional aggregometry did only reveal conclusive abnormalities in 33% of the patients with already diagnosed SPD, though they were very sensitive to detect abnormalities derived form ASA intake. PFA-100® with conventional COL-EPI cartridges was more sensitive than conventional aggregometry and detected abnormal closure times in 50% of the SPD patients. The PFA-100® facilitated the establishment of a more objective cut-off level for detection of abnormalities that circumvents the subjective interpretation of some aggregometric tracings. The use of the new experimental cartridges with COL, enhanced the sensitivity of the PFA-100® for the detection of altered platelet function in all SPD patients (100%). The combined use of COL and COL-AA cartridges improved the specificity of the PFA-100® test and could facilitate the development of a simple algorithm for the differentiation between aspirin-like defects and constitutive alterations of storage pool granules.