The LaboratoryMatters

Transcription

1 Laboratory Medicine Newsletter for clinicians, pathologists & clinical laboratory technologists. A Initiative. Complete Blood Count This issue highlights: CBC, while ubiquitous, is an excellent diagnostic test when performed correctly and reported by a laboratory medicine specialist. Pre-analytics: Blood Sample collection and preparation of Peripheral Smear Right sample = Right result Bad sample = Incorrect Result G-3, Ground Floor, Chaand Towers, 128 Lattice Bridge Road, Behind Jayanthi Theatre, Thiruvanmiyur, Chennai Tel: , Mobile:

2 COMPLETE BLOOD COUNT Blood count numbers tell many tales about the health of a patient. In this series we will cover the various clinical benefits of doing a CBC and how a laboratory medicine specialist analyses these numbers to enable the diagnosis of several conditions and diseases. The Complete Blood count is one of the most commonly ordered tests by the physician. It reflects the health of all the cellular elements in the blood. A CBC forms part of all health checks as a screen to detect a wide variety of diseases like anaemia, infection, inflammation, bleeding disorders, leukaemia etc. Today, most of the laboratories use automated cell counters to report the CBC. These cell counters range from a simple 3-part cell counter that reports parameters and a 5or 6 part cell counter that reports up to 30 parameters apart from several more that are used for research. These cell counters are fairly accurate and may be reported without verification. The cell counter gives out a wide array of parameters as numerical values, graphical representations of these values as histograms, scatter plots that afford better interpretation. It is important for the laboratory to share all relevant information with the physician. All abnormal CBC s should be verified by microscopic examination of the peripheral blood film by a competent and suitably qualified person. Any abnormality thus detected should be notified to the requesting physician. CBC, like most other laboratory test results is age and gender specific. It is the duty of both the reporting laboratory and the requesting physician to verify that the normal reference ranges provided by the laboratory are age and gender specific. All abnormal results should be flagged by the laboratory. The various red cell parameters that are part of the CBC are: Haemoglobin, haematocrit, Red cell count, Red cell indices that include, MCV, MCH, MCHC, RDW Haemoglobin is reported in g/dl and reflects the oxygen carrying capacity of the blood. Haemoglobin should be assessed along with all other red cell parameters.the total red cell count denotes the number of red cells or erythrocytes in circulation and is reported in million/cumm. Red Cell Indices MCV Mean Corpuscular lume or the average volume of the red cell is reported in femtoliters. A low MCV denotes a microcyte and a high MCV denotes a macrocyte MCH - Mean Corpuscular Haemoglobin or the average haemoglobin content in each red cell is reported in picogram. A low MCH means reduced haemoglobin content or hypochromasia and a high MCH would refer to hyperchromasia. 2

3 MCHC -Mean Corpuscular Haemoglobin Concentration is a measure of the concentration of haemoglobin in a given volume of packed red cells. It is reported in g/dl or %. MCHC is reduced in microcytic anaemia and is normal in macrocytic anaemia (due to the larger cell volume, though the amount of haemoglobin or MCH is high, the concentration remains normal). MCHC is increased in cases of Hereditary Spherocytosis, sickle cell disease and other haemoglobin disorders. RDW Red Cell distribution Width, refers to the spread of the red cells on the smear and their variation both in size, shape and haemoglobin concentration. A high RDW signifies a smear showing an increased variation in the red cells. This is referred to as anisopoikilocytosis (variation in size and shape). All the red cell parameters should be correlated with each other before release of the report. Anaemias are classified based on the red cell parameters and not on numerical values of hemoglobin alone. Microcytic Hypochromic anaemias (MCV and MCH ) They may be differentiated most often by careful observation of the CBC report. IDA has a low Hb, PCV, MCV, MCH and RBC count and a increased RDW BTT has a low or near normal Hb, PCV, low MCV, MCH, an elevated RBC count and a normal RDW BTT is diagnosed by estimating levels of HbA2 and HbF by HPLC. At, determination of Haemoglobin variant testing is done using HPLC and the interpreted is by an expert. Iron Deficiency Anaemia (IDA) Beta Thalassemia Trait (BTT) Sideroblastic anaemia Macrocytic anaemias (MCV MCH N) In this case, the MCV is usually greater than 100fL, MCH and MCHC may be slightly reduced and RDW is normal. Megaloblastic anaemia usually presents with pancytopenia Normochromic normocytic anaemias (MCV &MCH-N) In these cases, the Hb, PCV and RBC count is low while the red cell indices are normal. Every laboratory lays down a set of rules for review of peripheral blood films. These are based on the patient population catered to by the laboratory and national and international guidelines. In all these cases, the reporting pathologist reviews the slides and provides an opinion on the blood film wherever it is clinically relevant. 3

4 Severe anaemia may be the result of infection by intracellular parasites like Plasmodium Falciparum or Vivax, haematological malignancies like acute leukemia, plasma cell myelomas and non-hematological malignancies like gastric or colonic carcinoma. A careful interpretation of the CBC results including the scatter plots and histograms and a review of a well stained peripheral blood film is mandatory. The improved technology of the cell counters is a great help to the laboratory medicine expert to deliver credible, reproducible and meaningful reports effectively with a shorter turnaround time. PRE ANALYTICAL VARIABLES IN HEMATOLOGY LABORATORY Blood samples for hematology testing like Complete Blood Counts and Peripheral blood film examination are collected in tubes containing EDTA (Ethylene diamine tetra acetic acid). These tubes have a lavender colored cap/top. According to the NCCLS now known as CLSI (Clinical and Laboratory Standards Institute) guidelines, the anticoagulant of choice is the di-potassium salt of EDTA (K2 EDTA) at a concentration of mg/ml. Blood should be ideally collected in evacuated tubes according to the order of draw. After collection, it is mandatory that tubes be mixed by inversion at least 8-10 times for proper anticoagulation of blood sample. The tubes should be mixed before processing of sample also. Improper mixing leads to clot formation. Filling of tubes Megaloblastic anaemia due to Vitamin B12 or folate deficiency Alcoholic Liver disease Hypothyroidism Tubes should be filled to + 10% of the total volume Under filling of tube results in excess of anticoagulant and leads to erroneously low cell counts and PCV, morphologic changes like shrinking of red cells, staining alterations. Overfilling leads to improper and inadequate mixing and hence platelet clumping. The tubes should be processed on a cell counter within 4-6 hours of collection when stored and transported at room temperature. Prolonged storage of samples leads to erroneous results. Peripheral blood films should be made within 2 hours of sample collection. When smears are made later, numerous storage artifacts will be seen. This will affect the quality and interpretation of the results. Anaemia of chronic disorder like CKD, CLD, malignancies Anaemia of infection Aplastic anaemia Hemolytic anaemias 4

5 How Storage affects the sample? White Blood Cells WBC 1-3 hours: No problems >3-6 hours: Swelling, loss of granulation and structure > 6 hours: vacuolation, disintegration, decreased counts Erroneous reports from cell counters Neutrophil are counted as lymphocytes and monocytes Red Blood Cells RBC 6 hours: Crenation, sphering leading to MCV 6 hours at room temperature: MCV and PCV, TC and PLT Hemoglobin values are stable for up to 2 days Samples stored at 4-8o C are stable for 24 hours. Take home messages: Samples should be collected in K2 EDTA and mixed well Samples should be processed as soon as possible Inappropriate storage results in erroneous results Please share The LaboratoryMatters with your colleagues or write to us for a copy in your mail box. You can access this Newsletter at our website Questions or comments to newsletter@crestlaboratories.com, G3-Ground Floor, CHAAND TOWERS, 128, LATTICE BRIDGE ROAD, THIRUVANMIYUR, CHENNAI Phone: Mobile info@crestlaboratpories.com / crestlbaoratories@gmail.com 5