Saturday, February 13, 2010

General laboratory findings in clinical toxicology

                                                                             بسم الله الرحمن الرحيم
                                           General laboratory findings in clinical toxicology
1- Routine biochemical analysis: blood glucose, Electrolytes, blood
      gases, pH, plasma enzyme and Cholinesterase activity.
2- Hematological analysis: hematocrit, blood clotting, leukocyte count.
3- Clinical toxicology analysis: therapeutic drugs and drugs of abuse
1-Biochemical tests:
(a) Blood glucose
  ● Marked hypoglycaemia often results from overdosage  with antidiabetic drugs.
   ● Hypoglycaemia may also complicate severe poisoning with a     number of agents including iron salts and certain fungi.
    ● Hyperglycaemia is a less common complication of poisoning than hypoglycaemia, but has been reported after overdosage with acetylsalicylic acid, salbutamol and theophylline
(b) Electrolytes, blood gases and pH
   ● Acid-base and electrolyte disturbances occur in many types of poisoning for a variety of reasons:
  ● Coma resulting from overdosage with hypnotic, sedative, neuroleptic or opioid drugs is often characterized by hypoxia and respiratory acidosis.
   ● overdosage with salicylates such as acetylsalicylic acid initially causes hyperventilation and respiratory alkalosis, which may progress to the mixed metabolic acidosis and hypokalaemia characteristic of severe poisoning.
   ● Hypokalaemia and metabolic acidosis are also features of theophylline and salbutamol overdosage. 
          ● Toxic substances or their metabolites, which inhibit key steps in intermediary metabolism, are likely to cause metabolic acidosis owing to the accumulation of organic acids, notably lactate.
   ● Hyperkalaemia or hypernatraemia occurs in deliberate overdosage with potassium or sodium salts.
   ● Hyponatraemia can result from many causes, including water intoxication, inappropriate loss of sodium, or impaired excretion of water by the kidney.
   ● Hypocalcaemia can occur in ethylene glycol poisoning owing to sequestration of calcium by oxalic acid

 c) Plasma enzymes
   ● Shock, coma, and convulsions are often associated with nonspecific increases in the plasma or serum activities of enzymes (lactate dehydrogenase, GOT, GPT) commonly measured to detect damage to the major organs.
   ● The plasma activities of liver enzymes may increase rapidly after absorption of toxic doses of substances that can cause liver necrosis, notably paracetamol, carbon tetrachloride, and copper salts.
  ● Chronic ethanol abuse is usually associated with increased plasma gamma-glutamyltransferase activity. 

(d) Cholinesterase activity
  ● Systemic toxicity from carbamate and organophosphorus pesticides is due largely to the inhibition of acetylcholinesterase at nerve synapses.
  ● Cholinesterase, derived initially from the liver, is also present in plasma, but inhibition of plasma cholinesterase is not thought to be physiologically important.

  ● It should be emphasized that cholinesterase and acetylcholinesterase are different enzymes: plasma cholinesterase can be almost completely inhibited while erythrocyte acetylcholinesterase still possesses 50% activity
● In practice, plasma cholinesterase is a useful indicator of exposure to organophosphorus compounds or carbamates, and a normal plasma cholinesterase activity effectively excludes acute poisoning by these compounds.
  ● Erythrocyte (red cell) acetylcholinesterase activity can be measured, but this enzyme is membrane-bound and the apparent activity depends on the methods used in solubilization and separation from residual plasma cholinesterase.
  ● At present there is no standard procedure. However, low activities of both plasma cholinesterase and erythrocyte acetylcholinesterase is strongly suggestive of poisoning with either organophosphorus or carbamate pesticides.
2- Haematological tests
 (a) Blood clotting
 ● Prolonged prothrombin time is a valuable early indicator of liver damage in poisoning with metabolic toxins such as paracetamol.
 ● The prothrombin time and other measures of blood clotting are likely to be abnormal in acute poisoning with rodenticides such as coumarin anticoagulants, and after overdosage with heparin or other anticoagulants.
 ● Coagulopathies may also occur as a side-effect of antibiotic therapy.
(b) Carboxyhaemoglobin and methaemoglobin
 ● Measurement of blood carboxyhaemoglobin can be used to assess the severity of acute carbon monoxide poisoning and chronic dichloromethane poisoning. 
 ● Methaemoglobin (oxidized haemoglobin) may be formed after overdosage with dapsone and oxidizing agents such as chlorates or nitrites, and can be induced by exposure to aromatic nitro compounds.
(d) Erythrocyte volume fraction (haematocrit):
      - Acute or acute-on-chronic overdosage with iron salts, acetylsalicylic acid, indometacin, and other nonsteroidal anti- inflammatory drugs may cause gastrointestinal bleeding leading to anaemia.
       - Anaemia may also result from chronic exposure to toxins that interfere with haem synthesis, such as lead, or induce haemolysis either directly (arsine, see arsenic).
(e) Leukocyte count
  - Increases in the leukocyte (white blood cell) count often occur in acute poisoning, for example, in response to an acute metabolic acidosis . 
Determination of therapeutic drugs and drugs of abuse
(a) for treatment of  drug toxicity
(b) for forensic analysis.
(c) for determination of the levels of  drugs for   dosage adjustment
1- Drugs of abuse
Therapeutic drugs

Type of Drugs
Therapeutic level
Toxic level
Valporic acid (Depakine)
 50-100 µg/ml
> 100 - 150 µg/ml
Carbamazpine (Tegretol)
 4.0 – 12.0 µg/ml
> 12 µg/ml
0.9 - 2 µg/ml
> 2 µg/ml
10 – 20 µg/ml
> 20 µg/ml
Basic techniques for detecting drugs in serum and urine 
1- visible and ultraviolet  spectrophotometry
 The major  problem encountered with this technique is interference 
2- Thin-layer chromatography (TLC): 
      qualitative & confirmatory test
3- Enzyme Immunoassays (EMIT): 
his assay can detect     drug   levels in the nanomolar range and is both higly     sensitive and   specfic.
4- High performance liquid chromatography (HPLC): Preparative       
     HPLC & analytical HPLC. Not limited by the volatility or stability of the sample compound
5- Gas chromatography- mass spectrometry (GC/MS): Gold 
   standard technique to confirm the results obtained using EMIT and   
   TLC because of its great sensitivity and its reliability. This technique  
    is used in the forensic analysis. 
Drug levels in the blood with traditional drug dosing


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