Use for biochemical tests

Use for biochemical tests
Biochemical tests are performed for four main-reason diagnosis.
Diagnosis, management, prognosis and screening
Diagnosis
Biochemical tests very often help to confirm the diagnosis or identify a metabolic syndrome.
Management
Biochemical tests are most often used in the management of patients. Approximately 60-70% of all biochemical tests are used for monitoring treatment or follow the progress of the disease. For example, in patients with diabetic ketoacidosis frequent measurement of blood glucose helps to assess the response to insulin and adjust dosage.
Prognosis
Biochemical tests, either individually or in combination, can give an indication of the prognosis. For example, in patients with malignant tumours serial measurement of tumour markers is valuable in assessing the response to treatment and possibility recurrence.
Screening
When tests are done to detect the presence of disease before clinical features are evident, it is describe as screening.
Baseline
Biochemical testes are often also, before starting treatment, used as baseline to detect any harmful effects of treatment or to monitor the treatment.





Collection of specimens

Biochemical investigations are done in body fluid, most often in plasma or serum.
Inappropriate use of anticoagulant has often affect the results
For example taking a blood sample for electrolytes into an EDTA tube will cause very high potassium and low calcium concentration.

Blood for measurement of glucose should be taken into a fluoride tube, otherwise the blood glucose will artificially decrease due to the continued glycolysis by red cells.
Urine sample for calcium should be collected in a container with acid preservative to prevent precipitation of calcium phosphate.



Factors affecting test results

Test results can be affected by biological factors such as:
Age
Many biochemical variables vary with age. For example, Alkaline phosphates, phosphate and gonadotrophins are variant
Sex
Tests such as sex hormones, serum creatinine, urate and gamma glutamyl transferase show differences between sexes.
Body composition
Creatinine and creatine kinase, which are derived from muscle, are said to be related to muscle mass.
Triglycerides tend to be higher in obese individual.
Ethnicity/race
In healthy individual, prostate specific antigen is higher in black people and lower in Japanese compared to the white population. CK values in black population are higher than in Caucasians.
Stress
Stress causes the release of cortisol, ACTH, prolactin, growth hormone, etc. thus it is very important to avoid stress when taking sample for these measurements.
Food intake
Glucose, triglycerides and insulin are example of substances affected by food.
Drugs
Drugs can influence results by either interfering with the analysis or by a physiological mechanism, for example in patients taking phenytoin serum, gamma glutamyl transferase is higher due to enzyme induction.
Exercise
Exercise and trauma release CK and myoglobin.