The effect of pre-analytical variables on light transmittance aggregometry in citrated platelet-rich plasma from healthy subjects.

BACKGROUND: Although light transmittance aggregometry is considered the gold standard for platelet function testing, it is poorly standardized. The effect of several pre-analytical variables on this assay was investigated.

METHODS: Light transmittance aggregometry was performed with an automated coagulation analyzer using arachidonic acid (1.6 mmol/L), adenosine-5-diphosphate (ADP) (11 μmol/L) and collagen (11 mg/L, all final concentrations). The results were reported as maximum aggregation (in %) in 10 min. Twenty apparently healthy subjects were tested three times on two consecutive days: on day 1, fasting samples were collected in the morning and mid-day; on day 2, samples were collected in the morning after a light breakfast. Light transmittance aggregometry was performed immediately after preparation of platelet-rich-plasma (PRP), after stabilization (30 min) of non-adjusted and platelet count (225-275×10(9)/L) adjusted PRP, and at 2 and 4 h after blood collection.

RESULTS: Maximum aggregation was higher in the non-adjusted compared to the adjusted PRP with all three agonists used (all p<0.05). Arachidonic acid and ADP, but not collagen, induced maximal aggregation was significantly decreased after 4 h (arachidonic acid from 84%, 73%-90% to 71%, 28%-85%, p<0.001; ADP from 79%, 62%-87% to 66%, 50%-79%, p<0.001, medians with inter-quartile ranges). Short-term stabilization of PRP, consumption of breakfast and sampling at mid-day had no significant effect on maximal aggregation.

CONCLUSIONS: Blood collection and plasma preparation can be simplified by omitting short-term stabilization of PRP and adjustment for platelet count. The subjects can be tested from morning to mid-day, and a light breakfast is acceptable. However, the analyses should not be postponed for more than 2 h if arachidonic acid or ADP are used as agonists.