MLT GlobeForensic Science: Postmortem changes & time of death – page 2
35 Forensic Science MCQs on Postmortem changes & time of death with answers and explanations.
A markedly raised vitreous glucose at autopsy is most useful as evidence of:
Vitreous glucose falls after death through continued glycolysis, so low values cannot diagnose hypoglycaemia. A high value, however, indicates hyperglycaemia before death, as in uncontrolled diabetes.
Which postmortem analyte best supports a diagnosis of diabetic or alcoholic ketoacidosis?
Beta-hydroxybutyrate is the main ketone body in ketoacidosis and is relatively stable after death. Markedly elevated levels support ketoacidosis, while vitreous glucose helps distinguish diabetic from alcoholic causes.
Why can postmortem HbA1c be useful when blood glucose is unreliable?
HbA1c forms over the red cell lifespan and remains stable postmortem, reflecting average glucose over about two to three months, which helps document poorly controlled diabetes.
In forensic entomology, accumulated degree-days (or degree-hours) are used because:
Insects are cold-blooded, so development speed depends on ambient temperature. Summing heat units above a developmental threshold, using local weather data, converts observed stage into elapsed time.
When collecting fly larvae from a body, why are some kept alive and reared to adulthood?
Larvae of many fly species look similar, while adults are easier to identify. Accurate species identification is essential because developmental rates differ between species. Other larvae are killed and preserved to record their stage.
Compared with an antemortem thrombus, a postmortem clot is typically:
Postmortem clots form in static blood and often separate into red and yellow 'chicken fat' layers, lying free in the vessel. Antemortem thrombi are attached, laminated and granular.
Postmortem blood potassium is not useful for diagnosing antemortem hyperkalaemia because:
Loss of membrane integrity and haemolysis release intracellular potassium within hours of death, so blood potassium rises greatly regardless of antemortem value.
Raised postmortem C-reactive protein is most useful as a marker of:
CRP is relatively stable after death because it is synthesized only in the living liver. Elevated levels indicate an inflammatory response before death, supporting sepsis or other inflammatory conditions.
High ambient temperature affects rigor mortis by:
Heat speeds ATP depletion and later decomposition, so rigor appears and resolves sooner. Cold slows both, and rigor may persist for days in cold conditions.
Stiffening of a body exposed to intense heat, such as in a fire, is due to:
Heat denatures and coagulates muscle proteins, causing shortening and flexion (pugilistic attitude). This is a physical change unrelated to the time since death and must not be interpreted as rigor mortis.
Adipocere forms mainly when a body lies in:
Adipocere results from hydrolysis and hydrogenation of body fat into a waxy mass of saturated fatty acids, favoured by moisture and low oxygen, for example in water or damp graves. It usually takes weeks to months.
When sampling vitreous humor for potassium, which practice helps avoid a falsely high result?
Retinal cells contain high potassium. Forceful aspiration that includes cellular debris raises vitreous potassium, so slow aspiration, clear fluid and prompt centrifugation give more reliable values.
A postmortem vitreous pattern of high sodium, chloride and urea, with raised creatinine, suggests antemortem:
Vitreous sodium, chloride, urea and creatinine are relatively stable postmortem. Concurrent elevation of sodium, chloride and urea is the typical dehydration pattern; raised creatinine may suggest renal involvement.
Why should the soil around a body be searched when collecting insect evidence?
Mature post-feeding larvae leave the body to pupariate in surrounding soil or debris. Missing these oldest stages would underestimate the minimum postmortem interval.
In a suspected fatal anaphylaxis, which postmortem blood test is most useful?
Tryptase is released during mast cell degranulation and is relatively stable postmortem. A raised level, preferably from femoral blood, supports anaphylaxis, alongside specific IgE and circumstances.