Objectives:

Platelet radiolabeling in clinical routine usually results in labeling efficiencies (LE) above 80%. A variety of risk factors and clinical conditions are known to impair platelet labeling yield, among them elevated triglycerides and low-density lipoproteins. The potential influence of lipoprotein(a) (Lp(a)), an atherogenic lipoprotein particle containing a kringle subunit, which is widely found in the proteins of fibrinolysis pathway, has never been studied. Normal Lp(a) levels range below 30 mg/dl. The exact prevalence of elevated Lp(a) is unknown, most likely ranging below 10%. Even more rare is an isolated elevation despite an otherwise normal lipoprotein profile.

Methods:

We examined the role of isolated elevated Lp(a) (> 50 mg/dl, ranging up to 440 mg/dl) compared to patients with normal lipid profile. Platelets were radiolabeled with in-111-oxine at 37 °C for 5 minutes using ISORBE-consensus methodology.

Results:

The findings indicate that already at levels below 100 mg/dl Lp(a) decreases LE. LE assessment after cross-incubation of hyper-Lp(a) platelets with normal Lp(a) plasma and vice versa reveals that platelets rather than the plasmatic environment are responsible for the deterioration of labeling yield. This behavior already has been reported for elevated low-density lipoproteins. Apparently, the quantitative influence of LDL and Lp(a)/mg is comparable. Plotting the sum of LDL and Lp(a) versus LE reveals a clear significant negative correlation.

Conclusion:

As extremely elevated Lp(a), particularly above 150 mg/dl, may significantly impair labeling results. We therefore recommend to include extremely elevated Lp(a) into the list of parameters, which should be known before performing radiolabeling of human platelets.

Keywords: Platelet labeling,lipoprotein(a),labeling efficiency