Lab Workup to diagnose diseases, Various Types of samples, Factors Effecting the Tests

 How to diagnose diseases:

What are the various tests and their purpose to do:

Various types of tests:

• There are various tests done for various purposes to diagnose and monitor the disease. These are as follows:

1. Screening test: These are the simplest way to suspect disease like sugar in the urine indicate diabetes.
   1. 1.  Raised levels of PSA may need to rule out the possibility of prostatic cancers.
      2. Fecal occult blood may need to rule out colon cancer.
2. Diagnostic tests: These are specific tests to confirm the disease like colon biopsy to confirm colon cancer.
   1. 1. ECG to confirm heart disease.
      2. Hormones like T3, T4, and TSH to diagnose thyroid diseases.
3. Monitoring or follow up tests: These tests are done to know the progress of the disease e.g:
   1. 1. CA 125 may increase in the uncontrolled spreading of ovarian cancers.
      2.  ESR may become normal in the patient with tuberculosis.
      3. Serial estimation of liver enzymes gives the idea of improving or deteriorating liver function.
         

         various lab tests for the diagnosis of the diseases

4. Surgical procedures like a biopsy or FNA ( fine needle aspiration cytology ) may give the diagnosis of cancers or benign lesions e.g:
   1. 1. A liver biopsy may give us the grades of chronic hepatitis or malignancy.
      2. FNA of the breast is a very useful tool for diagnosis with an accuracy of above 95 % benign or malignant diseases of the breast.
5. Radiological procedures: Nowadays radiological procedures are advanced to diagnose various diseases of the bone like benign osteochondroma or malignant osteogenic sarcoma. Barium meal or Barium enema can diagnose GIT diseases.
6. Ultrasonography: This specialty has progressed a lot. It is a non-invasive procedure and very helpful to diagnose any mass in the liver, ovary or any other part of the body.
   1. 1. This can also be used for the follow-up of tumors.
      2. This can be used to guide the FNA procedures.
7. CT scan: This is computerized tomography and it gives more detailed information than a simple X-RAY.
   1. 1. This can also give a better estimate of the size of tumors.
      2. This is a very useful tool for the diagnosis of pathology of the brain like CNS tumors.
8. MRI: This is magnetic resonance imaging and is more accurate than a CT scan.
   1. 1. It can detect the tumor size of even 5 mm in diameter.
9. Examination of various body fluids: Body fluids like CSF, ascitic fluid, or Pleural fluids can also help in the diagnosis of various diseases.
   1. 1. like ascitic fluid cytology may tell you the presence of malignant cells.
      2. CSF examination differentiates various types of meningitis.

Various Specimens collected from the patient:

• There are the following body fluids samples used in the routine.

1. Venous blood: Venous blood is easy to collect and it tells the body’s physiologic condition.
   1. Most of the tests like LFT, Kidney function tests, CBC, and other biochemical tests are done on venous blood.
   2.  This sample can be collected by sterile needle from any prominent veins like arm, and hands.
   3. Risk: The major risk in this procedure is a local hematoma. and infection is almost nonexistent.
   4. Precaution: Don’t take the blood when the patients have an intravenous infusion.
   5. A fasting blood sample means a fast of 8 to 12 hours when no food or liquid is taken.
   6. The postprandial blood sample is taken after a meal.
   7. 2 hours of postprandial blood is taken in the patient with diabetes mellitus.
2. Arterial blood: Arterial blood is needed for the estimation of blood gases.
   1. The blood sample is usually taken from the femoral artery in the groin.
   2. The radial artery at the wrist.
   3. The brachial artery at the elbow.
   4. The neonates can get blood from the umbilical artery.
      1. To take blood from the artery needs an experienced person like a doctor or trained nurse or technician.
3. Capillary blood: The capillary blood is taken in the newborn or infants.
   1. Usually, the prick is done on the fingers or heel.
4. Serum: The whole blood is allowed to clot where all the clotting factors are removed by clotting.
   1. The best way is to keep the blood at 37 °C for 20 to 30 minutes then clear serum will come up leaving clotted blood at the bottom, Or you can centrifuge the blood to get the clear serum.
   2. Procedure to get good serum: 
      1. Take blood in the test tube and leave for 20 to 30 minutes and then centrifuge for 2 to 5 minutes and you will get the clear serum.
   3. Not good serum:
      1. If the serum has reddish color then discard it because it shows hemolysis.
      2. Hemolyzed serum interferes with the various tests.
   4. The serum is usually used for biochemical tests, hormones, and tumor markers.
5. Plasma: Plasma is obtained from the blood which contains an anticoagulant.
   1. Mix anticoagulant to the blood and centrifuge it,  will get a clear plasma at the top and bottom will have RBC, WBC, and some clotting factors and proteins.
   2. This can be used for various tests but not a good substitute for serum.
      

      Various blood samples

 

6. Pleural fluid: This fluid is present in the pleural space.
   1. This is taken out by the needle and the procedure is called Thoracentesis.
   2. This fluid is analyzed for the diagnosis of malignancy and may be used for culture and some biochemical tests.
7. Ascitic fluids: This fluid is collected from the abdominal cavity in case of ascites.
   1. This ascitic fluid may be analyzed to diagnose benign or malignancy. Also, some biochemical tests are done.
8. Synovial fluids: This is the joint fluid aspirated aseptically and its analysis gives the diagnosis for its formation.
9. Cerebrospinal fluid: This fluid is present in the spinal canal and brain.
   1. It is aspirated from the spinal canal aseptically.
   2.  This procedure is usually done by a physician or anesthetist.
   3. This fluid is used to diagnose various types of meningitis and can culture to find the causative organism.
10. Urine: Random samples may be taken for urine analysis.
    1. Or you can collect 24 hours sample for urinary protein, urea, creatinine, or other biochemicals.
       

       Body fluids sites

Factors affecting the lab tests:

1. Hemolysis: Whenever there is traumatic venesection that leads to hemolysis which is actually the rupture of the RBC.
   1.  These RBC release various enzymes and chemicals which interfere with the results. e.g. Potassium is quite high in haemolysed serum.
2. Anticoagulants if added in an increased amount will affect the results.
3. Temperature: Some of the tests are sensitive to a temperature where you may need frozen serum or plasma to preserve those chemicals. e.g ACTH level needs frozen plasma.
   1. While some tests need a serum to be at room temperature.
4. Fasting samples: Some of the tests needs fasting sample like fasting glucose level.
   1. For the Lipid profile, we need a fasting sample because on the random sample you will get higher values.
5. Drugs interference: Some of the drugs like aspirin, vit C, cold tablets pain reliever and antacids alter the test result.
6. Sleeping habits and diet: May alter the level of the hormone.
7. Blood sample taking method: e.g If you apply a tourniquet and take blood for calcium, the values will be not correct.
   1. If you squeeze the finger to get an adequate amount of blood then again the values will be less and not accurate because of the dilution effect.
8. While interpreting the values of a test to keep in mind age, sex, height, and weight.
9. Diurnal variation: Keep in mind the diurnal variation of some of the tests.
10. Exercise may affect the test results.
11. Food intake like:
    1. Food containing caffeine which may affect the tests.
    2. Smoking containing the nicotine will affect the tests.
    3. Alcohol intake will affect the tests.

Precautions before performing the lab tests:

1. This is best to perform all the tests within the first 45 minutes to one hour after collection.
2. Separate the plasma as soon as possible, don’t delay more than two hours.
   1. Premature separation of the serum will have microclots. It may block the pipettes.
   2. Coagulation in the plastic containers is delayed more than 20 to 30 minutes.
3. If delayed then properly store the sample at the appropriate temperature.
   1. If separation of the serum is delayed then keep the blood at room temperature to avoid hemolysis.
   2. If the test is not performed immediately then keep the serum at 4 °C.
   3. Centrifuge the tubes with the cap on it otherwise, there will be evaporation.
4. The serum is needed for electrophoresis.
5. For gases and ammonia whole blood is needed.
6. For clinical chemistry, the serum is the best option but plasma may be used.
   1. For plasma preparation, centrifuge the blood within one hour of sample collection for 10 minutes at 850 to 1000 X gravity.
7. Caped the bottle to avoid evaporation.

Abdominal tap for ascitic fluid:

1. This procedure is advised to tap peritoneal fluids.
2. usually, 20 to 18 gauge needle is used.
3. Usually use the lateral side of the abdominal wall, lateral to the umbilicus and this site is sterilized before doing the procedure.
4. One of the useful value in a peritoneal fluid is protein level which is low in transudate < 3 g/ dl and it is high in exudate > 3 g /dl, that may be due to inflammation or malignancy.
5. Unclotted blood indicates hemorrhage in the peritoneal cavity.
6. The presence Of inflammatory cells suggests Pancreatitis, appendicitis, rupture of organ, or malignancy.
7. Normally there are few mesothelial cells.

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