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in the previous issue of critical care , eslami and coworkers   review the various outcome measures used to evaluate the quality of blood glucose ( bg ) control ( level of ' tight glycaemic control ' [ tgc ] ) in critically ill patients ; the review considers studies published prior to 2008 .
they subdivided 30 different indicators into four nonorthogonal categories : bg zones ( adverse zones versus in - range zones ) , bg levels ( for example , mean bg ) , time intervals ( for example , time within a predefined bg range ) , and protocol features ( for example , bg sampling frequency ) . in recent years
, the definition of tgc had appeared to be well established , based on the findings of two randomized controlled clinical trials that clearly demonstrated the relation between strictly regulated bg ( 80 to 110 mg / dl ) and reduction in mortality / morbidity .
more recently , however , the level of tgc has emerged as a controversial issue , following publication of the findings of two other ( under - powered ) clinical trials that were unsuccessful in implementing tgc into daily practice .
control of bg to achieve a clinically and ethically approved target remains a crucial element in the treatment of intensive care unit ( icu ) patients and necessitates the design and assessment of measures that reflect this level of control .
the paper by eslami and coworkers presents an overview of existing indicators , but rigorous assessment to identify the optimal indicator(s ) is now required .
two important facts ( already partly discussed by eslami and coworkers ) must be emphasized .
first , there is no consensual definition of some methodologies that are currently used as an indicator .
eslami and coworkers identified 15 different thresholds for bg , varying from < 40 mg / dl to < 72 mg / dl . in some studies any measurement below the threshold is regarded ' hypoglycaemia ' , whereas other studies take the time dimension into account in order to ensure that multiple hypoglycaemic events occurring over a short interval ( for example , 30 minutes ) are evaluated as a single event . in still other studies , definitions
second , the availability of a near - continuous glucose sensor is a prerequisite for reliable tgc assessment , but no near - continuous glucose sensor has yet been found to be sufficiently reliable and accurate for use in critically ill patients .
accordingly , only time - discrete measurements of glycaemia ( for instance , a time interval of 1 hour or more ) are available , which can be dealt with in two ways . on the one hand ,
the time dimension can be neglected such that only the effectively measured values are considered in the analysis ( for example , mean bg , glycaemic penalty index ( gpi ) , and so on ) . as eslami and
coworkers correctly point out , this type of analysis may be sensitive to sampling . on the other hand ,
nonmeasured values can be estimated , leading to a ( non - measured ) continuous glucose signal , allowing application of area under the curve indicators ( for example , hyperglycaemic index [ hgi ] ) . here ,
however , a typically linear relation between observations is assumed ( in order to achieve an approximation to the true , nonlinear dynamics of bg fluctuation ) , which explains why this second technique can lead to incorrect assessment of bg signals . ideally ,
adequate assessment of a bg signal and comparison with other bg signals require the fulfilment of three conditions .
the first of these is consensus concerning the desired target bg range ( and definitions of hypoglycaemia / hyperglycemia ) .
the two landmark studies   and a new clinical trial   have shown that achieving age - adjusted strict normoglycaemia throughout the icu stay leads to lower icu mortality and morbidity , in both adult and paediatric icu patients .
second , the use of future reliable near - continuous glucose sensors will permit appropriate consideration of the time dimension in the indicator . accordingly ,
duration and magnitude of hypoglycaemic / hyperglycemic events are represented more precisely , as compared with time - discrete bg signals .
third , clinicians must be aware that traditional measures ( for instance , mean bg ) potentially can confound evaluation , as previously discussed .
more advanced indicators such as hgi and gpi ( note that gpi , introduced in 2008 , was not evaluated by eslami and coworkers ) are indispensable for adequate assessment of the overall level of bg control and are less complex than is sometimes claimed .
indeed , the hgi ( and , analogously , the hypoglycaemic index ) and gpi combine the first three categories mentioned by eslami and coworkers : bg zones , bg levels and time intervals . while we await the availability of near - continuous glucose monitoring devices , we advise clinicians to compute both hgi and gpi ( per patient ) , because these indicators compensate for each other 's weaknesses .
next , population hgi and gpi values can be obtained by computing the median and 25% to 75% interquartile range , because most bg distributions are non - normal .
finally , it is important to note ( particularly when comparing different bg signals ) the impact that study design ( bg sampling frequency and duration of algorithm application ) has on the level of bg control .
bg : blood glucose ; gpi : glycaemic penalty index ; hgi : hyperglycaemic index ; icu : intensive care unit ; tgc : tight glycaemic control .
bdm and gvdb are both supported by the flemish government ( fwo : g.0557.08 ) .
bdm is supported by the following : research council kul ( goa ambiorics , coe ef/05/006 , iofscores4chem , several phd / postdoc and fellow grants ) , the flemish government ( fwo : phd / postdoc grants , projects g.0452.04 , g.0499.04 , g.0211.05 , g.0226.06 , g.0321.06 , g.0302.07 , g.0320.08 , g.0558.08 , research communities ; iwt : phd grants , mcknow - e , eureka - flite+ ) , the belgian federal science policy office ( iuap p6/04 ) , eu ( ernsi ; fp7-hd - mpc ) , contract research ( aminal ) and helmholtz ( vicerp ) .
gvdb is supported by the following : research council kul ( goa/2007/14 , ot/03/56 ) , the flemish government ( fwo : g.0533.06 ) and the methusalem program , funded by the flemish government .
the article by eslami and colleagues provides an overview of the indicators used to measure the quality of blood glucose control in patients admitted to the intensive care unit . 
 each indicator can be related to one or more of the following categories : blood glucose zones , blood glucose levels , time intervals , and features of the insulin titration algorithm . 
 some important issues ( for instance those concerning the clarity of definitions used for glycaemic thresholds ) are raised . 
 this systematic review calls for a practical guide to advise the clinician how different blood glucose signals should ( ideally ) be evaluated and which steps should to be undertaken .