Dear Sirs,

We read with interest the article entitled ‘Impact of mean platelet volume on the occurrence and severity of sudden sensorineural hearing loss’ by Sagit et al. Reference Sagit, Kavugudurmaz, Guler and Somdas¹ In this important study, mean platelet volume, a determinant of platelet activation, was found to be elevated in patients with sudden sensorineural hearing loss.

Sudden sensorineural hearing loss is a symptom of cochlear injury. Potential aetiologies include vascular diseases, viral infections, allergic reactions, autoimmune disorders, use of medication and traumatic rupture of the intralabyrinth membrane, all of which can be related to mean platelet volume (as one aspect of platelet function).Reference Balta, Demirkol, Yildizoglu, Arslan, Unlu and Celik² A complete blood count is a relatively routine and inexpensive test which includes assessment of mean platelet volume.Reference Balta, Demirkol, Celik, Kucuk, Unlu and Arslan³ Platelet function can also be affected by vascular risk factors including age, smoking, diabetes mellitus, hypertension, hyperlipidaemia, metabolic syndrome and obesity, as well as by deep vein thrombosis.Reference Shin, Jung, Shim and Lee⁴

Mean platelet volume has also been related to peripheral artery disease, atrial fibrillation,Reference Balta, Demirkol, Kucuk and Unlu⁵ previous surgery, trauma, cancer, immobilisation, ulcerative colitis, coeliac disease and some medications.Reference Balta, Demirkol, Kucuk and Unlu^5, Reference Demirkol, Balta, Unlu, Yuksel, Celik and Arslan⁶ Inflammation plays a role in the pathogenesis of many diseases, such as Behçet's disease, in which mean platelet volume changes may occur.Reference Ekiz, Balta, Sen, Rifaioglu, Ergin and Balta⁷ Obstructive sleep apnoea syndrome may be associated with increased cardiovascular morbidity and mortality, platelet activation and increased mean platelet volume. Non-alcoholic fatty liver disease may be associated with cardiovascular risk; after controlling for other factors associated with non-alcoholic fatty liver disease, a significant correlation has been found between this disease and mean platelet volume.Reference Shin, Jung, Shim and Lee⁴

Finally, standardised laboratory methods are essential. In the methods section of Sagit and colleagues' paper, the nature of their biochemical analysis was not made clear. Likewise, the methods section did not define the mean platelet volume measurement technique. Platelets exhibit a time-dependent swelling when blood samples are anticoagulated with ethylene diamine tri-acetic acid (‘EDTA’), which does not occur in the presence of citrate. Thus, measurement of mean platelet volume in blood samples anticoagulated with ethylene diamine tri-acetic acid can be unreliable, since mean platelet volume increases significantly in a time-dependent manner following collection of blood samples prepared in this way.Reference Bath and Butterworth⁸ The optimal measurement time should be within 120 minutes of venepuncture, in order for comparison with reference ranges to be reliable.Reference Lancé, van Oerle, Henskens and Marcus⁹

In conclusion, mean platelet volume may be affected by many factors which need to be considered. It is difficult to adjust for all the variables listed above. In the absence of information on other overt inflammatory markers, an initial mean platelet volume value, taken alone, may not give clinicians reliable information regarding chronic endothelial inflammation.