Platelet Indices and Hyperglycaemia

1.7.1 Platelet Indices and Hyperglycaemia

Platelet indices are a group of platelet parameters measured using an automated haematologic analyser and includes platelet count, mean platelet volume (MPV), platelet distribution width (PDW) and platelet-larger cell ratio (P-LCR) (Budak et al., 2016). MPV quantifies the average size of the platelet population. It is used as a biomarker for platelet activation because the larger platelets tend to be younger and more reactive (Grove et al., 2011). MPV is associated with cytokines (e.g. thrombopoietin, interleukin (IL)-6 and IL-3) that regulate megakaryocyte ploidy and platelet number, and result in the production of larger platelets (Budak et al., 2016). When platelet production is decreased, younger platelets become bigger and more active, and MPV levels increase. PDW is an indicator of volume variability in platelet size and reflects the heterogeneity in platelet morphology, and P-LCR is an indicator of circulating larger platelets (>12 fL), presented as a percentage (Budak et al., 2016).

Several studies have investigated the relationship between MPV and hyperglycaemia ex vivo. The majority of them found a positive correlation between high MPV and HbA1c in type 2 diabetic patients (Demirtunc et al., 2009; Kodiatte et al., 2012; Ozder and Eker, 2014; Ulutas et al., 2014). However, data from Hekimsoy et al. (2004) found no relationship between HbA1c and MPV (see table 1.2).

Data from studies investigating the relationship between MPV and FBG is more inconsistent. Some report a strong relationship between FGB and MPV in type 2

25 diabetic patients (Kodiatte et al., 2012; Ozder and Eker, 2014; Ulutas et al., 2014) and other studies found no relationship (Demirtunc et al., 2009; Hekimsoy et al., 2004) (see table 1.3). In addition, Shimodaira et al. (2013) found a relationship between MPV and FBG in prediabetic subjects. The contradictory data from ex

vivo studies questions the use of MPV as a marker for cardiovascular risk in

patients with hyperglycaemia.

Although the data is contradictory for correlations between MPV and hyperglycaemia, several studies have calculated a significant difference between type 2 diabetic patients and non-diabetic subjects (Demirtunc et al., 2009; Kodiatte et al., 2012; Ozder and Eker, 2014; Ulutas et al., 2014). These include studies that found no relationship between MPV and HbA1c (Hekimsoy et al. (2004) and Pananas et al. (2004) (see table 1.4), indicating that additional factors are involved.

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Table 1.2: Relationship between MPV and HbA1c in type 2 diabetic patients

Source of data MPV (fL) (mean + SD) HbA1c (%) (mean + SD) R value P value n Kodiatte et al (2012) 8.29 + 0.735 9.13 + 2.5 0.29 <0.001 300 Demirtunc et al. (2009) 8.7 + 0.8 8.4 + 1.2‡ _{0.394 0.001 35}

Ozder and Eker (2014) 10.66 + 0.94 8.80 + 1.62 0.357 0.000 201

Ulutas et al. (2014) 8.3 + 1.3 9.6 + 2.3‡ _{0.393 <0.001 32}

Hekimsoy et al. (2004) 10.62 + 1.71 7.49 + 1.5 -0.033 0.74 NS 145

‡_{Diabetic cohort with an HbA1c >7% was used. NS: data is not significant.}

Table 1.3: Relationship between MPV and FBG in type 2 diabetic patients

Source of data MPV (fL) (mean + SD) FBG (mmol/L) (mean + SD) R value P value n Kodiatte et al (2012) 8.29 + 0.735 8.35 + 3.98 0.269 <0.001 300

Demirtunc et al. (2009) 8.7 + 0.8 12.21 + 4.2‡ _Not

reported

NS 35

Ozder and Eker (2014) 10.66 + 0.94 12.25 + 3.50 0.306 0.000 201

Ulutas et al. (2014) 8.3 + 1.3 13.68 + 4.57‡ _{0.41 <0.001 32}

Hekimsoy et al. (2004) 10.62 + 1.71 9.38 + 2.89 0.099 0.24 NS 145

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Table 1.4: Mean MPV in type 2 diabetic subjects and non-diabetic subjects from six separate literature sources

Source of data MPV (fL) in non-

diabetics (mean + SD) N MPV (fL) in type 2 diabetic patients (mean + SD) n P value Kodiatte et al (2012) 7.47 + 0.726 300 8.29 + 0.735 300 <0.001 Demirtunc et al. (2009) 8.2 + 0.7 40 8.7 + 0.8‡ _{35 0.002}

Ozder and Eker (2014) 10.04 + 1.01 201 10.66 + 0.94 201 0.000

Ulutas et al. (2014) 7.1 + 1.0 40 8.3 + 1.3‡ _{32 <0.001}

Hekimsoy et al. (2004) 9.15 + 0.86 100 10.62 + 1.71 145 0.00

Pananas et al. (2004) 7.1 + 1.2 151 14.2 + 2.2 131 0.01

‡_{Diabetic cohort with an HbA1c>7% was used. This cohort is considered to have uncontrolled}

diabetes. All studies used the unpaired t-test except those marked with a ‡ _{that used the one-way}

ANOVA.

In contrast to the data shown in table 1.4, Shlomai et al. (2015) calculated an MPV of 9.2 + 1.3 fL for both diabetic and non-diabetic patients (n=82 and n=86, respectively). This is an important finding because this was a well-designed study with stringent exclusion criteria. The two groups were matched for age, body mass index (BMI), hypertension, hyperlipidaemia, smoking, medication, co- morbidities and renal function. All diabetic subjects had well controlled glycaemia (the mean HbA1c was 49.7 mmol/mol) and no prior ischemic events. Conversely, the limitation of the study was that the diabetic patients had good glycaemic control so any possible effects caused by chronic hyperglycaemia may not have been observed.

28 It is interesting to note that there was no correlation for MPV vs. duration of diabetes (Kodiatte et al., 2012; Demirtunc et al. 2009; Hekimsoy et al., 2004) and no significant correlation was shown for MPV vs. vascular complications (Demirtunc et al., 2009; Kodiatte et al., 2012). Demirtunc et al. (2009) hypothesised that this was caused by the rapid consumption of activated platelets in diabetic patients with complications. This is supported by literature that investigated MPV in other diseases. For example, Bilen et al (2015) found a decrease in MPV in non-diabetic patients with renal failure. In patients with high- grade inflammatory disorders such as rheumatoid arthritis and systemic lupus erythematosus, MPV can be low during the active stage of the disease, suggesting that the larger, more active platelets are consumed at the sites of inflammation (Gasparyan et al., 2011).

Although the majority of the literature indicates that MPV is increased in type 2 diabetic patients compared to those without diabetes, it is important to note that there was no definitive explanation for this outcome. For example, ex vivo studies cannot demonstrate whether the high MPV is simply caused by osmotic swelling due to raised levels of glucose metabolites. Alternatively, the increased MPV in type 2 diabetes could be an indication of a direct increase in thrombopoiesis or enhanced platelet turnover caused by their propensity to atherosclerosis. Therefore, if an atherosclerotic plaque ruptures, platelets are required to plug the damaged site and so the bone marrow produces more platelets (Kodiatte et al. 2012).

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