Correlations between Transcranial Doppler Velocities and Laboratory Markers of SCA Severity

Introduction. Stroke is one of the main complications of Sickle Cell Anemia (SCA), occurring in about ten percent of the affected individuals before the age of twenty. Hydroxyurea (HU) currently used to treat SCA, although its exact mechanism of action remains not fully understood. The transcranial Doppler (TCD) is used to detect the risk of stroke in children with SCA, which measures the time-averaged mean of the maximum velocity (TAMMV) in the internal carotid artery and the middle cerebral arteries. TAMVV above 200 centimeters per second (cm/s) is associated with a high risk of stroke. In the present work, we evaluated the correlations between laboratory markers and TCD velocities and we also studied the influence of HU in different TCD groups. Material and methods. A cross-sectional study including 164 HbSS patients with average age 7.51±4.14 was conducted at the Pediatric Professor Hosannah de Oliveira Hospital (HUPES/UFBA) and in the Sickle Cell Disease Reference Center, hospitals located in Salvador and in Itabuna, both cities in northeastern Brazil. The risk of stroke was assessed by TCD, for three outcomes were considered: TCD1 for the normal group (TAMMV <170 cm/s), TCD2 for the conditional group (TAMMV 170-199 cm/s) and TCD3 for the high risk (TAMMV> 200 cm/s). The legal representatives signed the informed consent terms. The study was approved by the Research Ethics Committee and was conducted in accordance with the guidelines of the Declaration of Helsinki and its revisions. Hemoglobin profiles were confirmed by high-performance liquid chromatography (HPLC). Hematological analyses were carried out using an electronic cell counter. Biochemical and inflammatory analyses were performed by immunochemistry assays and immunoassays. Statistical analyses were performed on Graphpad prism 6.0. The distribution of quantitative variables was analyzed using the Shapiro-Wilk test. The median of quantitative variables between three or more groups was compared using One-way Anova/Kruskall-Wallis for nonparametric data. When comparing two groups, Mann-Whitney t-tests were performed. The correlation analyses were performed between variables using Spearman coefficient (r). Results. We observed negative correlations (with Spearman r< -0.2 and p<0.05) between left and right TAMMV and red blood cell (RBC) count, hemoglobin levels and hematocrit. There were positive correlations (Spearman r> 0.2 and p<0.05) with mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), Red Cell Distribution Width (RDW), white blood cell (WBC), lymphocytes, reticulocytes percentage, aspartate aminotransferase (AST) and total bilirubin. By comparing the three TCD groups, excluding the stroke group, nitric oxide (NO) levels (p=0.157) and mean platelet volumes (MPV) (p=0.0134) varied between groups, with the lower numbers observed for the TCD2 and TCD3 groups. WBC count is progressively increased in DTC groups (DTC3>2>1), but not significantly. The lymphocyte count (p=0.006) was increased in the TCD3 group, as compared to the other two groups. Ferritin median values were increased (p=0.005) in TCD2 and TCD3 groups. The MPV values were lower in TCD2 and TCD3 groups both for HU treated and untreated patients (p=0.032), with the lowest MPV values observed for TCD3. WBC count was significantly different among TCD groups of untreated patients (p=0.009) but not among TCD groups of patients treated with HU. Patients in use of HU showed decreased WBC counts in all TCD groups, but only in a significant way for TCD3 (p=0.002). In the same line, the lymphocyte counts were significantly decreased by HU in TCD 1 and TCD3, (p=0.04 and p=0.006) but not for TCD2.

Conclusions. The current results show significant correlations between TCD-TAMMV and laboratory markers commonly used to monitor SCA pediatric patients. These laboratory parameters included reticulocyte percentage and white blood cell counts, which are known markers of SCA severity, but their correlations with TAMMV has never been shown before. We also show that hydroxyurea treatment had different impacts on laboratory parameters such as MPV, lymphocyte and leukocyte numbers in the different TCD groups evaluated here. We speculate that the association of these markers with TCD should be further studied and carefully analyzed along with TCD velocities.