Quick guide to Laboratory Medicine: a student's overview

Armando Guerra-Ruiz, Bernardo Lavin, Mayte Garcia Unzueta

• Publisher: Discover Bioworld
• Year: 2017
• ISBN:
  9783962551742
• Topic: Medicina
• Subtopic: Tecnologia e forniture mediche

This book provides an overview of useful laboratory tests as complementary tests for the diagnosis of common ailments and diseases in standard medical practice. The reader will find a concise but detailed guide to the tests, their rationale and their interpretation.

Chapter 1. Emergency Laboratory

Emergency Laboratory

The clinical laboratory plays an essential role in the functioning of the hospital emergency services and others that require a fast response time. Response time is directed influenced by the characteristics of the patient attended (intensive care unit, day hospital, dialysis, etc.)

Not all biological quantities that can be measured in a clinical laboratory are of interest to be measured in an emergency laboratory. In some cases it is straight forward to determine if a test is of interest for urgent measurement; however in other cases this distinction is not so clear and there is still controversy about the usefulness of some metabolites in an urgent medical intervention. It is useful to consult local entities (societies, associations, legal obligations, etc.) to determine the extent of an urgent medical laboratory pipeline.

Some of the aspects to take into account when designing an emergency laboratory would be:

• Definition of the role and tasks of the emergency laboratory. Integration in the dynamics of hospital emergency care. Extension to cases of admissions that require a rapid response. Preanalytic, routes of arrival of the samples, control of labeling, different biological samples, purpose, and importance of the conditions of the sample.
• Determinations that are made in the emergency laboratory. Analysis of biochemistry, hematology, elemental and sediment, analysis of arterial and venous gasometry, hormones of urgency, osmolarity of biological fluids. Integration in clinical care.
• Request processing system. Contact and familiarization with the request handling system. Management of the computerized laboratory system (LIS). Functioning of the LIS. Interaction with the Hospital Information System (HIS). Interaction of the LIS with the automatic analyzers used in the emergency laboratory. Common problems and their solution or treatment. Interaction with the results viewer.
• Biochemistry of Emergencies. Main determinations. Determinations available in the catalog. Principles and rationale of the determinations. Methods and techniques. Analytical techniques available in analyzers. Possible interferences. Range of normality, range of technique. Alarm values. How to deal with alarm values. Most of these determinations are also performed in the routine biochemistry laboratory so the list of determinations are detailed in Annex 1.
• Hormones of emergency. Available analytical techniques. Determinations available in the catalog. Principles and basis of operation of the determinations. Possible interferences. Range of normality, range of technique, and alarm values. Cases of pre, intra and post-surgical analyzes.

Emergency biochemistry.

Automated analysis using the Dimension X pand plus (Siemens Healthcare) analyzer. Spectrophotometry techniques. Main markers of serum, urine or biological fluids. Acquisition of skills in the management of equipment, calibration of techniques, internal quality control, maintenance and problem solving, cooperation and communication with faculties. Communication with technical support.

An example of biochemical parameters pipeline for an emergency laboratory can be consulted in appendix 1.

Emergency hematology.

The hemogram is a complementary test considered as basic in any emergency department, both hospital and prehospital. The three cell blood series (red blood cells, leukocytes and platelets) are counted. The number and differentiation of leukocytes is reported. For its correct valuation must take into consideration not only its percentage value but also the absolute figures. The objective of this study is to help establish a diagnosis, although it can also serve as a prognostic factor and as a control of the evolution of a disease.

For these reasons, white blood cell count is one of the usual tests to be performed on every patient entering, regardless of disease. Second, we find the count of the red series: Hematocrit, Hemoglobin, Hematocrit, Mean Corpuscular Volume, Mean Corpuscular Hemoglobin, Medium Corpuscular Hemoglobin Concentration, which can be affected in both acute (blood loss) and chronic (Anemia of chronic diseases, iron deficiency anemia, etc.).

Finally, as regards the number of platelets, it is very important to note that we can find false low platelet numbers due to the existence of platelet aggregation, either spontaneously, by agglutinins or by a clot due to a defective extraction of blood.

Emergency Urinalysis

Urinalysis (Elemental and Sediment). The study of the sediment of the urine is a simple and valuable diagnostic method for its profitability. The procedures used to perform the systematic analysis of urine are physical examination (color, turbidity ...), chemical analysis by means of the test strip (density, pH, protein, glucose, ketones, bilirubin , Urobilinogen, nitrites, leukocytes and hemoglobin) and finally the microscopic study of the sediment that must be performed when the chemical analysis is altered and we can show the presence of cellular elements (leukocytes, red blood cells and different types of epithelial cells), cylinders (Cell hyaline, granular or wax), bacteria, yeasts, parasites whose presence guides us to different pathologies.

Urinalysis (Elemental and Sediment). Physical analysis (color, turbidity ...), chemical analysis by means of the test strip (density, pH, proteins, glucose, ketones, bilirubin, urobilinogen, nitrites, leucocytes and hemoglobin) and microscopic study of the sediment: presence Of cellular elements (leukocytes, red cells and different types of epithelial cells), cylinders (hyaline cells, granuloses or waxes), bacteria, yeasts, parasites whose presence guides us to different pathologies. Particularities of the determinations in the area.

Arterial blood gas analysis.

Arterial blood gas analysis is a common complementary technique in the diagnostic procedures of emergency medicine. Its usefulness in assessing the respiratory status and the acid-base balance of the patient that constitute its primary indications is reinforced because it is an economical procedure that is easy to interpret and lacks contraindications. The blood sample for blood gas analysis should be collected in a heparinized syringe. The parameters that are analyzed in the gasometry are: PaO2, PaCO2, HCO3, PH, Excess of bases and O2 arterial saturation.

PaO2: Indicates the amount of O2 that is dissolved in blood and is an expression of alveolar pressure of O2. Their normal values oscillate between 80 and 100 mm Hg. Figures below 60 mm Hg will always be indicative of respiratory failure.

PaCO2: Indicates the amount of CO2 dissolved in the blood, and is a direct expression of lung ventilation. It participates in the regulation of blood pH together with the bicarbonate buffer system. Their normal numbers oscillate between 37 and 43 mm Hg. Hypercapnia occurs in all those processes that involve alveolar hypoventilation, either due to central or peripheral causes or as a compensatory mechanism in cases of metabolic alkalosis.

PH: Their normal values oscillate between 7.37 and 7.43 and their changes may be induced by variations of PaCO2 and bicarbonate concentration and depending on these two parameters can be classified in alkalosis or respiratory or metabolic acidosis.

HCO3: Their normal values oscillate between 22 and 26 mEq / liter. Its variations cause alkalosis or acidosis of metabolic origin.

Excess bases: Concentration of bases in whole blood measured under optimal respiratory conditions. Their normal values oscillate between + -2 and its alteration is always indicative of metabolic origin.

SatO2: The percentage of hemoglobin that is saturated with O2. Their normal values are between 94 and 98%. A value below 90% always indicates respiratory failure.

Biological fluids

There are two samples to analyze biochemical parameters: plasma and serum. The plasma is collected in a tube that carries as anticoagulant heparin lithium and is recognized by its green plug. It is the most used in the laboratory of Emergencies since almost all the determinations are realized in plasma. The serum is collected in a tube that has a gel separator and is recognized by its metallic stopper and pink. We will only use serum for the determination of Troponin.

Cerebrospinal, synovial, ascitic, peritoneal, pleural and cardiac fluids are analyzed in the emergency room laboratory....