Interpretation of Laboratory Data

Laboratory test results are used to investigate potential problems with a patient’s anatomy or physiology. The pharmacists usually monitor laboratory tests to:

• Assess the therapeutic and adverse effects of a drug
• Determine the proper drug use
• Assess the need for additional or alternate drug therapy
• Prevent test misinterpretation resulting from drug interference

Normal laboratory test results fall within a predetermined range of values, and abnormal values fall outside that range. The results of most laboratory tests are reported with a reference range numerical range of results for that investigation when performed for a healthy subject (in the absence of significant disease). 

The values outside the normal range may not necessarily indicate disease or the need for treatment. Conversely, if a result falls within the quoted reference range this does not necessarily guarantee the absence of disease or abnormal organ function. For these reasons, it is important that a clinical pharmacist should interpret results with reference to the clinical status of the patient and other relevant information. 

A clinical pharmacist must be able to interpret lab data for a number of reasons:

• Laboratory data can provide guidance regarding the appropriateness of the patient’s current drug therapy. The results may suggest that a particular drug is inappropriate for the patient and should therefore be discontinued or avoided (e.g.: NSAID for a patient with severe renal impairment.
• It can also be used as a guide to determine the adequacy of drug response.
• The measurement of blood glucose parameters when assessing the effectiveness of insulin treatment.
• Monitoring for the efficacy of treatment.
• A laboratory test can also be used to check for signs of severe drug toxicities that may be reflected by abnormal biochemical or hematological parameters or elevated liver function tests.

Rational for Ordering Laboratory Test

Laboratory tests are performed with the expectation that the result will help a practitioner or patient in the following;

• Discovery of occult disease
• Confirming the suspected diagnosis after signs and symptoms appear
• Differential diagnosis of a disease
• Determining the stage or activity level of the disease.
• Determining the recurrence of disease
• Evaluating the Effectiveness of Therapy

A laboratory test can also be subdivided into discretionary and screening tests. The screening test is performed without clinical indication either on hospitalized patients or healthy outpatients for the early or preventive diagnostic measure. Screening tests are more valuable when the disease is common salient and treatable.

The discretionary investigation could include items 2-6 of the test above. The prescriber performs discretion based on the provisional diagnosis or proposal for treatment. The lab investigation involves the estimation of the following samples

• Urine
• Sputum
• Blood
• CSF
• Faeces
• Peritoneal fluid

Laboratory data can be classified as follows based on the organs whose functions are analyzed.

1. Hematological test
2. Liver function test
3. Renal function test
4. Cardiac function test Stool microscopy
5. Culture sensitivity
6. Pulmonary function test
7. Thyroid function test

ALSO READ: Therapeutic Drug Monitoring (TDM)

1. HAEMATOLOGICAL TEST

Hematology provides information about cellular components and non-cellular components. The routine test include

• RBC count, WBC count, Hemoglobin level, Hematocrit
• RBC indices: MCV, MCH, MCHC
• Reticulocyte count
• ESR
• Platelet count
• Bleeding time
• Clotting time
• Prothrombin time

2. LIVER FUNCTION TEST

• It helps in measuring hepatic or biliary inflammation and also helps to assist liver synthetic and functional capabilities including albumin, globulin, and prothrombin time. 
• Liver function tests help to find out cholestatic disease through the measurement of alkaline phosphate ALP and gamma-glutamyl transpeptidase (GGT). 
• Hepatocellular injury can also rule out by measuring aspartate aminotransferase (AST) and alanine aminotransferase (ALT).

3. RENAL FUNCTION TESTS

• Renal function tests are used to measure the functioning capacity of the kidney and also for measuring GFR. The tests include BUN and serum creatinine. 
• By using creatinine clearance we can adjust the dose, and assessment of acute and chronic renal failure, glomerular nephritis, nephritic syndrome etc.

4. CARDIAC ENZYMES

• These tests are specific to evaluate unstable angina, Myocardial infarction and ischemic heart disease. 
• To assess the cardiac function test such as biochemical tests ECG and noninvasive imaging techniques can be done. The cardiac enzymes are CKMB and LDH (lactate dehydrogenase). C-reactive protein and amyloid –A protein are also used to detect cardiac problems.

5. CEREBROSPINAL FLUID

• CSF analysis is done to find any infections. In CSF analysis protein, glucose, and chlorides are measuring. Viral infections also affect CSF.

6. STOOL EXAMINATION

• Stool microscopy can be done in case of any blood tinch in stool or faeces occult.

7. CULTURE SENSITIVITY

• The samples are cultured and the sensitivity and resistant pattern of microorganisms can be done. It will help to appropriate therapy.

8. PULMONARY FUNCTION TEST

• This test is useful in the case of respiratory diseases it will help in the diagnosis, evaluation, and monitoring of disease. By performing PFT lung damage, obstruction and restrictive disease can be detected. 
• PFT includes lung volume and lung flow tests. Lung volume tests are tidal volume, vital capacity, total lung capacity, residual volume etc. The latter include FEV, FEV1, FVC, and PEFR.

9. THYROID FUNCTION TESTS

• This test is used to find out hypothyroidism and hyperthyroidism. Hypothyroidism may be due to a defect in the thyroid, in the pituitary or the hypothalamus. By measuring the amount of T3, and T4, TSH can differentially diagnose the severity.
• Thyroid function tests include: - measurement of T3 AND T4. Evaluate the integrity of the hypothalamus, pituitary, and Thyroid axis. Assess inherent thyroid gland function and detect antibodies.

ALSO READ: Drug Information Resources