Low cholesterol as a risk factor for primary intracerebral hemorrhage: A case-control study: A comment on the study.

Sir,

We read with interests on Valppil et al.'s study discussing the relationship between cholesterol level and primary intracerebral hemorrhage (ICH).[1] Valppil claimed to perform a case-control study and concluded that low cholesterol is a risk for primary ICH. In our points of view, it might be premature to conclude the risk factor association based on their study design. In case–control study, the risk (low cholesterol) should be identified before the event (ICH) onset. On the contrary, Valppil et al examined ICH patients’ serum cholesterol level 48 hours after ICH had occurred. On account that acute ICH may raise one's catecholamine and thus increased lipid metabolism. The reduced cholesterol level may be a consequent result from acute ICH rather than a risk factor for it.

Without obtaining pre-hemorrhagic cholesterol status, a conclusion of risk factor could not be made but associated instead. Take one study, for example, in 2009, Orken conduced a study[2] similar to Valppil et al.'s one; 259 primary ICH cases were compared with 137 healthy controls. Serum cholesterol level was taken 24 hours after acute cerebrovascular event. The cholesterol level in cases was significantly lower than that in the controls. A conclusion of lower cholesterol is “association with” primary ICH had been made in that study. Based on Valppil et al.'s study design, a result that low serum cholesterol is only “associated with” rather than “risk for” acute intracerebral hemorrhage can be concluded.