Lab Workup to Diagnose Diseases

• There are various tests to diagnose diseases. We can discuss the tests used to diagnose diseases one by one.

What are the various types of tests to diagnose diseases?

• Various tests are performed to diagnose and monitor diseases. These are as follows:

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

4. Surgical procedures:
   1. These are like a biopsy or an FNA (fine-needle aspiration cytology), which may provide a diagnosis of cancer or a benign lesion.
   2. A liver biopsy may give us the grades of chronic hepatitis or malignancy.
   3. FNA of the breast is a very useful tool for diagnosis with an accuracy of above 95% for benign or malignant breast diseases.
5. Radiological procedures: 
   1. Nowadays, radiological procedures have advanced, enabling the diagnosis of various bone diseases, such as benign osteochondroma and malignant osteogenic sarcoma.
   2. A Barium meal or a Barium enema can diagnose GIT diseases.
6. Ultrasonography:
   1. This specialty has progressed a lot. It is a non-invasive procedure and helps diagnose any mass in the liver, ovary, or any other part of the body.
   2. This can also be used for tumor follow-up.
   3. This can be used to guide the FNA procedures.
7. CT scan: 
   1. This is computerized tomography, and it gives more detailed information than a simple X-RAY.
   2. This can also provide a better estimate of tumor size.
   3. This is a very useful tool for diagnosing brain pathology, such as CNS tumors.
8. MRI: 
   1. This is magnetic resonance imaging and is more accurate than a CT scan.
   2. It can detect a tumor as small as 5 mm in diameter.

What is the significance of tests in various body fluids?

1. Body fluids such as CSF, ascitic fluid, and pleural fluid can also help diagnose various diseases.
2. Ascitic fluid cytology may indicate the presence of malignant cells.
3. CSF examination differentiates various types of meningitis.

What are the various samples collected from the patients?

• The following body fluid samples are used in routine testing.

Venous blood: 

1. Venous blood is easy to collect, indicating the body’s physiologic condition.
2. Most tests, such as LFTs, Kidney function tests, CBC, and other biochemical tests, are performed on venous blood.
3.  This sample can be collected using a sterile needle from prominent veins like the arms and hands.
4. Risk:
   1. The major risk in this procedure is a local hematoma, and infection is almost nonexistent.
5. Precaution:
   1. Don’t take the blood when the patient has an intravenous infusion.
6. A fasting blood sample:
   1. This sample refers to a fast of 8 to 12 hours during which no food or liquid is taken.
7. The postprandial:
   1. This is the blood sample taken after a meal.
8. Two hours after a meal, postprandial:
   1. This is the blood sample taken in the patient with diabetes mellitus.

Arterial blood: 

1. Arterial blood is needed to estimate blood gases.
2. The blood sample is usually taken from the femoral artery in the groin.
3. The radial artery at the wrist.
4. The brachial artery at the elbow.
5. Neonates can receive blood from the umbilical artery.
   1. Drawing blood from an artery requires an experienced person, such as a doctor, trained nurse, or technician.

Capillary blood:

1. Capillary blood is taken in newborns or infants.
2. Usually, the prick is done on the fingers or heel.

Serum: 

1. Whole blood is allowed to clot, during which all the clotting factors are removed.
   1. The best way is to keep the blood at 37 °C for 20 to 30 minutes, then the clear serum will separate, leaving the clotted blood at the bottom; or you can centrifuge the blood to obtain the clear serum.
2. Procedure to get good serum: 
   1. Take blood in the test tube, leave it 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 is reddish, discard it because it shows hemolysis.
   2. Hemolyzed serum interferes with the various tests.
   3. Serum is usually used for biochemical tests, hormone assays, and tumor marker assays.

Plasma: 

1. Plasma is obtained from the blood, which contains an anticoagulant.
2. Mix the anticoagulant into the blood and centrifuge it. We will get clear plasma at the top and bottom, with RBCs, WBCs, and some clotting factors and proteins.
3. This can be used for various tests but is not a good substitute for serum.

Pleural fluid: 

1. This fluid is present in the pleural space.
   1. The needle removes this fluid, and the procedure is called Thoracentesis.
   2. This fluid is analyzed to diagnose malignancy and may be used for culture and biochemical tests.

Ascitic fluids: 

1. This fluid is collected from the abdominal cavity in case of ascites.
2. This ascitic fluid may be analyzed to diagnose benign or malignancy. Also, some biochemical tests are done.

Synovial fluids:

1. This is the joint fluid aspirated aseptically, and its analysis diagnoses its formation.

Cerebrospinal fluid:

1. This fluid is present in the spinal canal and brain.
2. It is aspirated from the spinal canal aseptically.
3.  A physician or anesthetist usually does this procedure.
4. This fluid is used to diagnose various types of meningitis and can be cultured to find the causative organism.

Urine:

1. Random samples may be taken for urine analysis.
2. You can also collect 24-hour samples for urinary protein, urea, creatinine, or other biochemicals.

What factors affect the lab tests?

Hemolysis: 

1. Whenever there is traumatic venesection that leads to hemolysis due to rupture of the RBC.
2.  These RBCs release various enzymes and chemicals which interfere with the results. e.g., Potassium is quite high in haemolysed serum.

Anticoagulants:

1. If added, an increased amount will affect the results.

Temperature: 

1. Some tests are temperature-sensitive, and frozen serum or plasma may be needed to preserve those chemicals. For example, the ACTH level needs frozen plasma.
   1. Some tests need serum to be at room temperature.

Fasting samples:

1. Some tests require fasting samples, such as fasting glucose levels.
2. We need a fasting sample for the Lipid profile because you will get higher values on the random sample.

Drugs interference: 

1. Some drugs, such as aspirin, Vitamin C, cold tablets, pain relievers, and antacids, can alter test results.

Sleeping habits and diet:

1. It may alter the hormone levels.

Diurnal variation:

1. Keep in mind the diurnal variation of some of the tests.

Exercise:

1. It may affect the test results.

Food intake, such as:

1. Food containing caffeine, which may affect the tests.
2. Smoking containing nicotine will affect the tests.
3. Alcohol intake will affect the tests.

What precautions will you take when taking a blood sample? 

1. If you apply a tourniquet and then take blood for calcium testing, the values will not be accurate.
   1. If you squeeze the finger to obtain sufficient blood, the values will be less accurate due to the dilution effect.
2. When interpreting test results, keep in mind age, sex, height, and weight.

What precautions will you take before performing the lab tests?

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

How will you do the abdominal tap for ascitic fluid?

1. Tapping peritoneal fluids is advised during this procedure:
   1. Usually, an 18- or 20-gauge needle is used.
   2. Usually, the lateral side of the abdominal wall, lateral to the umbilicus, is used; this site is sterilized before the procedure.

3. One of the useful values in peritoneal fluid is the protein level, which is low in transudate (<3 g/dL) and high in exudate (> 3 g/dL). The high protein may be due to inflammation or malignancy.
4. Unclotted blood indicates hemorrhage in the peritoneal cavity.
5. The presence of inflammatory cells suggests pancreatitis, appendicitis, organ rupture, or malignancy.
6. Normally, there are few mesothelial cells.

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