ORIGINAL ARTICLE Erythrocyte sedimentation rate of human blood exposed to low-level laser Mustafa S. Al Musawi 1,2 & M. S. Jaafar 1 & B. Al-Gailani 2 & Naser M. Ahmed 1 & Fatanah M. Suhaimi 3 & Muhammad Bakhsh 1 Received: 27 January 2016 /Accepted: 24 May 2016 # Springer-Verlag London 2016 Abstract This study is designed to investigate in vitro low- level laser (LLL) effects on rheological parameter, erythrocyte sedimentation rate (ESR), of human blood. The interaction mechanism between LLL radiation and blood is unclear. Therefore, research addresses the effects of LLL irradiation on human blood and this is essential to understanding how laser radiation interacts with biological cells and tissues. The blood samples were collected through venipuncture into EDTA-containing tubes as an anticoagulant. Each sample was divided into two equal aliquots to be used as a non- irradiated sample (control) and an irradiated sample. The ali- quot was subjected to doses of 36, 54, 72 and 90 J/cm 2 with wavelengths of 405, 589 and 780 nm, with a radiation source at a fixed power density of 30 mW/cm 2 . The ESR and red blood cell count and volume are measured after laser irradia- tion and compared with the non-irradiated samples. The max- imum reduction in ESR is observed with radiation dose 72 J/ cm 2 delivered with a 405-nm wavelength laser beam. Moreover, no hemolysis is observed under these irradiation conditions. In a separate protocol, ESR of separated RBCs re- suspended in irradiated plasma (7.6 ± 2.3 mm/h) is found to be significantly lower (by 51 %) than their counterpart re- suspended in non-irradiated plasma (15.0±3.7 mm/h). These results indicate that ESR reduction is mainly due to the effects of LLL on the plasma composition that ultimately affect whole blood ESR. Keywords Low-level laser . Erythrocyte sedimentation rate . Red blood cells . Blood plasma Introduction Laser therapy has its own significance in medicine depending on its application [1]. Various low-level laser (LLL) wave- lengths with different power and exposure time have been utilized in blood therapy for a variety of clinical applications because of its ability to modulate blood rheology and improve microcirculation [2, 3]. The low power does not damage the hydrogen bonds in the tissues and does not result in any change except the photochemistry effects by stimulating a cell through an increased cellular metabolism [4]. LLL therapy does not cause thermal effects; therefore, it will not damage living cells [1, 5, 6]. To observe LLL irradiation effects on living biological sys- tem, photons must be absorbed by electronic absorption bands belonging to some molecular chromophore or photo acceptor [7]. The interaction mechanism between LLL radiation and blood is unclear, consequently resulting in complications in LLL therapy of blood due to the numerous reactions that take place simultaneously [8]. Therefore, the study of the effects of LLL irradiation on human blood is important for a better un- derstanding of the mechanisms involved in the interaction of laser radiation with biological tissues. The rheological properties of the blood are being reported as modified by LLL irradiation when blood samples are ex- posed to a red spectrum in the visible range with a power of <100 mW [9]. This treatment is incredibly effective for eryth- rocyte aggregation; it decreases haematocrit (HCT), blood * Mustafa S. Al Musawi laser_mu@yahoo.com 1 School of Physics, Universiti Sains Malaysia, 11800 Pulau Pinang, Malaysia 2 Department of Physiology, College of Medicine, Al-Mustansiriya University, Baghdad, Iraq 3 Advanced Medical and Dental Institute, Universiti Sains Malaysia, Bertam 13200, Kepala Batas P. Pinang, Malaysia Lasers Med Sci DOI 10.1007/s10103-016-1972-1