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replication with induced activation of inflammatory and coagulation pathways.18The mechanisms involved are multifactorial and complex.
It was noted that the mean D-dimer level reduced from 343.11±151.370ng/ml in the first year (0-1) of therapy to 219.50±59.397ng/ml in the second year (1-2). This was later followed by an increment in the third (2-3) and a secondary drop in the fourth year (3-4) of therapy but the mean D-dimer level was still less than the mean level in the first year (0-1) of commencement of HAART, P=0.279.
Highly active antiretroviral therapy (HAART) can suppress HIV replication for extended periods resulting in substantial reductions in chronic immune system activation and inflammatory cytokine production leading to a reduction in D-dimer levels and mortality in HAART-experienced patients.136
Several studies have indicated that HAART reduces the level of biomarkers, including D-dimer, in HIV patients. El-Sadr et al found that levels of hs CRP, IL–6 and D-dimer were reduced by effective ARV therapy. 17Baker et al observed a significant reduction in D-dimer but not IL–6 and hs CRP after starting ARV therapy, while interruption of ARV therapy led to an increase in these biomarkers. 136Kuller et al also demonstrated an increase in these biomarkers upon discontinuation of ARV therapy, and the increase was found to be associated with an increase in HIV–RNA levels.18In other studies by Hougaard et al187, Hamlyn et al188, Kaplan et al189 and in the STACCATO trial189reduced D-dimer levels were also observed in HIV treatment-experienced patients on HAART.
Neuhaus et al in a comparison of inflammation biomarkers observed a significantly higher level of markers including IL–6, CRP and D-dimer in HIV positive subjects both on and off ARV therapy compared with HIV negative control, suggesting that viral suppression alone may not be sufficient to counter the factors driving inflammation in this population. 104
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It was also observed in this study that HAART-experienced subjects have slightly higher mean CD4+ T-cell count (387.55 ± 334.85cells/ul) than HAART-nạve subjects (379.33 ± 287.25 cells/ul), though this difference was not statistically significant (P = 0.906). This could be explained by the fact that HIV infection leads to a specific decline in the CD4+ helper T cells, resulting in inversion of the normal CD4/CD8 T-cell ratio. The major mechanism for CD4+ T cell depletion is programmed cell death (apoptosis), which can be induced by HIV through multiple pathways.52,53,54The HAART-experienced subjects has been associated with significant and prolonged immunologic reconstitution, characterized by increased CD4+ T-cell count, reduced opportunistic infections and prolonged survival
77, 78. While in HAART-naive individuals HIV infection is typically characterized by a rise in plasma HIV RNA (viral load) and a decline in CD4+ T-cell count. If left untreated, this eventually leads to opportunistic infections, development of AIDS and AIDS-related deaths.56,59
In his study, Erhabor et al observed that after 12 weeks of HAART in HIV infected subjects and untreated HIV infected controls there was a mean increase in CD4+ T-cell count of 39cells/ul in subjects on HAART while untreated controls showed a mean decline of 12 cells/ul.83 Jeremiah et al,190 and Owiredu et al191, in similar studies also found that HAART improves CD4+T-cell count.
No correlation was observed between CD4+ T-cell count and D-dimer level in HAART-experienced and HAART-nạve subjects with r=0.031, P=0.850 and r=-0.196, P=0.225 respectively. The interplay between D-dimer levels, CD4+ T-cell counts and plasma HIV RNA is complex with dynamic changes after ART initiation.136Jeremiah et al observed a negative correlation between CD4+ T-cell count and D-dimer level in HAART-experienced and HAART nạve subjects.190While Borges et al observed a positive correlation between CD4+ T-cell count and D-dimer level in HAART-experienced subjects, which was surprising and counter-intuitive.192
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An association between CD4+T-cell count and D-dimer levels has been observed in several other studies, Crum-Cianflone et al19and Rasmussen et al113 found that risk of Venous Thromboembolism are associated with low CD4+ T-cell counts. Ahonkaiet al112and Saif et al20in previous studies also found a significantly increased risk of VTE in HIV infected patients with a low CD4+T-cell count (below 500 and 200 cells/ul respectively). This appears to be a result of immune / inflammatory activation causing increased D-dimer concentrations, which induces a hypercoagulable state. In contrast, Jacobsen et al found no association between CD4+ T-cell count and risk of VTE. 119 In the present study, males were observed to have lower mean D-dimer level, (307.99±170.98ng/ml) than females (359.84±192.69ng/ml) and the difference was not statistically significant (P=0.211).Lee et al found that women had significantly higher fibrin D-dimer levels than men.193Borges et al while studying factors associated with D-Dimer Levels in HIV-Infected Individuals found that black race, female sex were demographic factors independently associated with higher D-dimer levels.192Borges et al further hypothesized that the significantly higher D-dimer levels observed in younger women may be due to higher estrogen levels and higher immune activation.192 Pregnancy, hormone replacement therapy and estrogen-containing contraceptive pills increase plasma levels of procoagulant factors in females and are well-known risk factors for thromboembolism.In contrast, Al-Zahrani et al found no sex differential in plasma D-dimer levels.194
It was also noted in this study that Age have no significant influence on the D-dimer level, though D-dimer was much lower among the younger subjects, 18-25 years age bracket (284.89±60.65ng/ml) than older age group, 56 – 60 years (422.10ng/ml).But, there was no correlation between Age and D-dimer in this study, r = -0.141 ,P=0.213.
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Several studies have indicated that D-dimer concentration were positively associated with increasing age.177,178 Borges et al found that a significant increase in D-dimer occurs with age in HIV positive men and that HIV positive women have high D-dimer levels from an early age.192Deleterious interactions between vascular damage, co-morbidities, inactivity and activated inflammation have been postulated as possible mechanisms for increased levels of D-dimer with aging.192
In HAART-nạve and HAART-experienced subjects smoking had a significant effect on D-dimer level (P=0.039) with smokers having a lower mean D-D-dimer level of 224.87±57.00ng/ml than non smokers, 343.55±186.93ng/ml. Alcohol and BMI (kg/m2) did not have significant effect on D-dimer level, P=0.115, P=0.988 respectively.
Lee et al observed that current smokers had higher fibrin D-dimer levels than ex- or never-smokers.193In contrast there are also reports of no difference in D-dimer level between smokers and nonsmokers.194 Alcohol and BMI are also other factors which have been associated with increased D-dimer level.192
Haematological manifestations have been documented to be the second most common cause of morbidity and mortality in HIV patients. 195,196,197
The findings in this study showed no improvement in haematocrit (PCV) and haemoglobin concentration. The mean haemoglobin concentration /packed cell volume for HAART-nạve subjects was 11.23 ± 1.76 g/dl /34.95 ± 5.34% and HAART experienced subjects was 11.12 ± 1.90 g/dl/ 34.30 ± 5.81%. This difference in the mean PCV and haemoglobin concentration between HAART nạve and experienced study subjects was not statistically significant. P=0.606, 0.789 respectively. No correlation was observed between Haemoglobin concentration / packed cell volume and D-dimer in HAART experienced subjects. A weak but statistically significant negative correlation was observed between
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D-dimer, Haemoglobin concentration r=-0.391, P=0.013 and packed cell volume (PCV) r=
-0.382, P=0.015 in HAART nạve subjects.
Anaemia is common in HIV-infected individuals and the mechanism of anaemia range from decreased red cell production, ineffective production and increased red cell destruction and HAART has also been observed to correct or improve the anemia but the mechanisms are not yet fully understood.7The incidence and severity of the cytopoenia generally correlate to the stage of the disease with anaemia being the most commonly encountered haematologic abnormality and a significant predictor of progression to AIDS or death.198It is also important to note that most of my subjects were on zidovudine (AZT) and it has been reported by several authors to cause anaemia by inhibition of haemoglobin synthesis and toxicity to bone marrow cells, particularly, erythroid lines.199
Though most studies have reported improvement in haematocrit and haemoglobin values resulting in reduction in morbidity and mortality of HIV patients on HAART.191,198,200HAART-nạve patients have been observed to have a high risk of developing reduced PCV compared to their counterparts on HAART.191Odunukwe et al in his study on the Haematological and biochemical response to treatment of HIV-1 infection with HAART observed a significant increase in the haematocrit and haemaglobin level after 12 weeks of HAART.198This may indicate the effectiveness of HAART in reducing viral load and improving haemotocrit values. Omoregie et al reported no improvement in haematocrit values of HAART treated HIV patients compared with HAART-nạve patients in his study.199This is similar to the observation in this study which showed no improvement in heamatocrit values of HAART, treated HIV patients compared with HAART-nạve patients.
The mean white cell count (WBC) in this study was 5.29±1.97 x109/L for HAART-experienced subjects,which is slightly higher compared to 4.83±2.32 x 109/L for HAART-
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nạve subjects, but the difference was not statistically significant P=0.350.The WBC showed no correlation with D-dimer in the HAART experienced subjects (r=-0.096, P=0.555) and HAART nạve subjects (r=0.078, P=0.633).
Multiple etiologies may be responsible for neutropenia in HIV infection, which may occur, either singly or in combination.7Drug induced and antibody mediated neutropenia has been reported and the use of HAART has been associated with improvement of leukopenia and neutropenia in treated patients.7Odunukwe et al in a study reported that the range of total WBC count in the HIV-positive group was not different from what was recorded for the normal population. 198This is in agreement with the finding in this study and could be as a result of leucocytosis that may follow malaria infection or any opportunistic infection, which may have masked the leucopenia that was supposed to have been recorded at baseline. In contrast,Owiredu et al, reported a significantly lower WBC value for HAART experienced patients when compared to their nạve counterparts.191
The mean platelet count was increased in this study for HAART-experienced subjects (246.40±106.22 x109/L) in comparison to HAART-nạve subjects (226.05±92.94x109/L).Though the improvement was not statistically significant P=0.365.
Both HAART experienced and nạve subjects showed no correlation between platelet count and D-dimer level r=0.004 P=0.979, r=0.090 P=0.579 respectively.
Several mechanisms has been postulated for thrombocytopenia in HIV infection, these include increased platelet destruction (as in de novo ITP and primary HIV-associated thrombocytopenia (PHAT)), decreased platelet production (due to reduced megakaryocyte differentiation) and infection of megakaryocytes by human immunodeficiency virus (resulting in damage to the HIV-infected megakaryocytes).7Effective use of HAART probably significantly decreases HIV viral load and, in so doing, ameliorates many of the effects of HIV on megakaryocytes, platelet
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production, and destruction.7The finding in this study is in agreement with Attili et al, who observed increased platelet count in HAART-experienced subjects. In contrast, Owiredu et al observed that HAART though effective in improving haematocrit and decreasing the prevalence of anaemia could lead to a decrease in platelet counts.191
CONCLUSION
The study has been able to document the presence of elevated D-dimer level among HIV treatment-nạve patients in comparison to HIV treatment-experienced patients in Port-Harcourt, Nigeria. Data from this study also suggest that HAART reduces D-dimer level significantly in HAART-experienced subjects, thereby reducing the risk of thrombosis.
These findings are in support of existing literatures.
RECOMMENDATION
Since the subjects in this present study are few, a cohort study using a larger population to confirm these findings is recommended.
It is suggested that D-dimer should also be further studied to ascertain its usefulness in assessing risk of thrombosis in HIV infection.
Finally, a risk stratification system or screening tool for VTE should be developed for HIV patients, as this will help to reduce morbidity and mortality. This system should involve CD4+ T-cell count and D-dimer assay, since these investigations are less expensive and easily accessible in a resource-constrained environment like Nigeria.
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