Calculation Information and Courses from MediaLab, Inc.
These are the MediaLab courses that cover Calculation and links to relevant pages within the course.
Learn more about laboratory continuing education for medical technologists to earn CE credit for AMT, ASCP, NCA, and state license renewal and recertification. Or get information about laboratory safety and compliance courses that deliver cost-effective OSHA safety training and continuing education to your laboratory's employees.
|Calculating and Reporting the Myeloid:Erythroid (M:E) Ratio|
Once the bone marrow cell count is completed and recorded, the M: E ratio should be assessed. This is performed by calculating the total myeloid precursors in proportion to the total erythroid precursors. Remember that this does not use the total white blood cell tally; the myeloid cells alone are counted, excluding lymphocytes, monocytes, macrophages, plasma cells, megakaryocytes, osteoclasts, osteoblasts, and other non-myeloid cells. In most circumstances, it is quite simple to divide the myeloid total by the erythroid total to find the ratio. This is always reported as a whole number ratio, and is normally around 3:1 (reference range= 2:1 to 4:1). In some situations where the erythroid portion is increased, or the myeloid series is decreased, the M:E ratio is reversed. This would still be expressed as a whole number ratio (example: 1:2). A simple way to perform the calculation is to always divide the larger value by the smaller. Which side of the colon, the 1 is placed on, is dependent on which cell type was larger. The 1 always belongs on the side of the cell type found in lower numbers.For example:Myeloid total 120 : Erythroid total 40 M:E ratio = 120 ÷ 40 = 3 or 3:1 So, the M:E ratio is 3:1Another example:Myeloid total 30 : Erythroid total 150Divide the larger number by the smaller (notice that the placement is reversed).150 ÷ 30 = 5 So, the M:E ratio is 1:5
|Calculation of CSF Cell Count|
In general, use the following equation to calculate CSF cell count: Cells/µL = # of cells counted x dilution / # of large squares counted x 0.1µL (chamber depth)For an undiluted specimen in which 10 squares are counted: (total cells counted x 1) / (10 squares counted x 0.1µL) = cells per µLTherefore, in this example: (total cells counted) / (1µL) = cells per µL1µL = 1 mm3
|WBC Correction for Traumatic Tap|
A calculation is used to correct CSF WBC counts which are falsely increased due to a traumatic tap:
WBCs added = WBC(blood) x RBC(CSF) / RBC(blood)The blood WBC count is multiplied by the ratio of the cerebrospinal fluid RBC count to blood RBC count.The result is the number of artificially introduced WBCs. The true CSF white cell count is then calculated by subtracting the artificially introduced WBCs from the actual CSF WBC count.
If the patient's peripheral WBC and RBC counts are within normal limits, some laboratories use the following formula:
Subtract one white cell from the CSF WBC count for each 750 RBC counted in the spinal fluid.
|Introduction to Statistics|
Statistics is the branch of mathematics that deals with the organization, analysis, and interpretation of information. It is often said that statistics is the opposite of probability. A probability question would be, "If I have a fair coin and toss it ten times, how often will I get seven or more heads?" A statistics question would be "I toss a coin ten times and get seven heads. Given this information, how likely is it that this coin is fair?"Many people are uncomfortable with statistics. Statistics is one of the more confusing mathematical subjects, and deals with many subtle concepts. Often the interpretation of a result is more difficult than calculating the result in the first place. This course will attempt to make clear both the calculations and the interpretation of those results.
The mean, also called the arithmetic mean or the average, is simply the sum of all the data points divided by the number of points. It is denoted with . The formula for the mean is: For example, here are the number of hours that some students worked on a project: # hours worked 46285The average time spent working was: The average is the most common way of calculating central tendency. Some of its characteristics are: easy to calculateonly one exists for any data setaffected by all observations, and therefore strongly affected by outliersused in many statistics calculations
The mode is the value that occurs most frequently in a data set. There can be more than one mode, if there are two or more values that are tied for being most likely. The properties of the mode are: requires no calculation not necessarily unique very insensitive to extreme values may not really be close to the center of the distribution
|Standard Deviation Example|
Now we will do an example calculation of the standard deviation of a set of data. Here are the data we will use:Table VII Urea Nitrogen Concentration in Five EmployeesConcentration (mg/dL)97111310
|Using the Coefficient of Variation|
In the clinical laboratory, the coefficient of variation is used for two main purposes:Aid in the selection of a new method for routine use. Monitor the inherent variability (precision) of a method already in routine use.Selection of a new method for routine use requires comparative precision data. If the two methods being compared have different means and/or units, calculation of their CVs provides the comparison. (However, if two methods have the same units, and measure the same quantity, but have different means, this could be a sign that one of the instruments is calibrated incorrectly.)
|Analyzing the Mixing Study Results (cont.)|
Various tools have been developed that identify whether a sample is "corrected" or "not corrected" by the addition of pooled normal plasma. One tool is the Rosner Index.The Rosner Index subtracts the clotting time of the pooled normal plasma (PNP) from the clotting time of the 1:1 mix. This result is then divided by the clotting time of the patient sample. The equation is as follows:Rosner Index = (1:1 mix clotting time result - PNP clotting time result) / initial prolonged clotting time of patient sampleWith this method, a high index value represents the possibility of an inhibitor. A low index value would represent a possible factor deficiency. For example, an index of 10 or lower indicates correction, 15 and above indicates no correction. If after the calculation is performed and a value of 10-15 is obtained, it is recommended that your test be repeated.Each laboratory must determine its own reference interval for the Rosner Index.
|Mixing Study Methodology Differences|
Most clinical laboratories will use a 1:1 mix when performing mixing studies; however, some will use various dilutions of patient plasma and pooled normal plasma for their protocols.In addition, the analysis of the mixing study involves interpreting the pre- and post-mix results. This can be performed using various methods including: the Rosner Index, the <70% correction formula, or a laboratories own calculation and cut-off value. Finally, it is suggested that each laboratory test the sensitivity of their PT and aPTT reagents before running mixing studies. The sensitivity of the reagent system can be tested by running dilutions of the pooled normal plasma controls with specific factor deficient plasma. This ensures that the system will detect a normal result, even if the factor level is as low as 40%.
|Estimated Average Glucose|
Estimated average glucose (eAG) is a glucose concentration level calculated from a patient's HbA1C result. In 2008, the ADA recommended the use of this new term and that this calculation be performed and reported routinely with the measured A1C result. The formula for conversion of HbA1C to glucose in mg/dL is eAG = 28.7 x A1C – 46.7. A web calculator is located at: http://professional.diabetes.org/glucosecalculator.aspx. Accessed January 11, 2010.
|When evaluating the throughput of a particular method you should consider all of the following except:||View Page|
Numerous studies have shown that, if administered correctly, RhIg is effective at preventing D immunization. To work, RhIg must be given in sufficient dose, and it must be given before Rh immunization has begun.Unfortunately, despite RhIg's proven efficacy, some women continue to make anti-D in the perinatal period. Such 'failures' are mainly (but not totally) due to human error. Examples of how women may still produce anti-D some 40+ years after the implementation of RhIg prophylaxis: Immunization to D occurred before the administration of RhIg, e.g., before 28 weeks gestation*; Immunization to D occurred after the administration of RhIg at 28 weeks and before delivery because an antenatal fetomaternal hemorrhage (FMH) occurred that was too large for residual passive anti-D to give protection; Female was already immunized from a prior pregnancy but anti-D was too weak to be detected in antibody screen tests prior to RhIg administration; RhIg dosage was insufficient to clear a larger fetal bleed at delivery (e.g., FMH screen was not done or a false negative occurred); Incorrect calculation of RhIg dosage; RhIg administered too late , e.g., well after 72 hours of delivery; Antenatal RhIg not given, e.g., mother had no, or limited, access to prenatal care, or did not seek it, and a FMH occurred during pregnancy; Failure of physician to carry out prenatal blood testing; RhIg not given due to laboratory clerical or technical error in Rh typing the mother or child; RhIg not given in cases such as abortions, ectopic pregnancies, and trauma (e.g., car accidents).* Because anti-D production before 28 weeks is rare (the order of 0.24% to 0.31%), RhIg's use earlier in pregnancy is not recommended. It is not cost effective and would expose most women to an unneeded blood product.
Transferrin saturation (TS) is usually reported along with the serum iron (SI) and total iron binding capacity (TIBC). TS indicates the percent of iron binding sites on transferrin that are carrying iron. TS is derived from a calculation using the formula:TS =(SI/TIBC) x 100TS results are reported as percentages. Typical reference intervals for TS are 20% to 55% for males and 15% to 50% for females. TS is currently considered to be a good test for screening persons for hereditary hemochromatosis (HH) due to its sensitivity and specificity for iron overload. It may be elevated prior to significant deposition of tissue iron. TS levels increase as additional iron is accumulated.A drawback to using the TS is that it is dependent on performing both the SI and TIBC. The unsaturated iron-binding capacity UIBC may be a lower cost alternative.The optimal TS criterion for detecting HH is controversial. Using a TS of >60% for males and >50% for females has been found highly accurate in detecting abnormal iron metabolism in persons with HH. Others studies suggest using lower TS levels, e.g. 45%, as a criterion indicating further testing is warranted. Current guidelines from the American College of Physicians include a TS cutoff level of >55% for identifying iron overload. (11)Patients with initially increased TS should be followed by performing a second TS from a fasting morning specimen. The patient should also be advised not to take vitamins supplemented with iron or oral contraceptives for several days prior to the repeated test. TS levels may be affected by diurnal variation, dietary factors, and co-existing disease states such as inflammation and hepatitis. Patients with HH may have falsely normal TS if chronic blood loss or inflammatory disease is present.
|Calculating Absolute Cell Counts|
Lymphocytes are a specific type of white blood cell. Lymphocytes can either be T cells or B cells. In the mature T cell population, the T cells can either be helper T cells or suppressor/cytotoxic T cells.Understanding the principles behind the identification of these T cell populations is important. To begin, CD3 marks all mature T cells. Then: CD4 marks T-helper cells CD8 marks cytotoxic T cells Therefore, in any given lymphocyte population, the CD4+ cells plus the CD8+ cells should equal the CD3+ cells. This is because the CD4 cells and the CD8 cells will also mark with CD3 since they are both mature T cells.Provided the total white blood cell (WBC) count and the percentage of lymphocytes from a complete cell count/differential, one can calculate various values. These values include: absolute CD3 counts, CD4 counts, CD8 counts, and CD4:CD8 ratios.The following results represent a patient sample which is used to calculate the values above:WBC count= 2.5 cells/uL (2500 cells/L), % Lymphs= 30%Using the following calculation: Absolute (Abs) lymphs= WBC count x 1000 x percent lymphs (expressed as a decimal) we can determine the absolute lymphocyte count per liter.2.5 x1000 x 0.30 = 750 lymphs/L
|Calculating Absolute Cell Counts- continued|
Now that the absolute lymphocyte value has been calculated, the results from the flow cytometric analysis can be incorporated as follows:Values from the flow cytometer analysis%CD3= 60% (CD3 positivity reflects total T cell percentage)%CD4= 40% (CD4 positivity reflects T-helper cell percentage)%CD8= 20% (CD8 positivity reflects cytotoxic T cell percentage)*Note that 60% CD3 (total mature T cells) is further broken down into 40% CD4 (T-helper cells) + 20 % CD8 (cytotoxic T cells)By using the following calculation, the absolute (Abs) cell CD marker populations = Abs lymphocytes x % CD (as decimal)For Example:AbsCD3= 750 x 0.60 = 450 cells/LAbsCD4= 750 x 0.40 = 300 cells/LAbsCD8= 750 x 0.20 = 150 cells/LCD4:CD8 ratio= 40/20 = 2.0
|Example Regression Line Calculation|
The following example will clarify how to use the preceding equations: Point x y y2 (x-) (y-) (x-)(y-) (x-)2 (y-)2 xy 1 6 11 121 -8 -6 48 64 36 66 2 8 8 64 -6 -9 54 36 81 64 3 11 14 196 -3 -3 9 9 9 154 4 13 23 529 -1 6 -6 1 36 299 5 16 18 324 2 1 2 4 1 288 6 16 21 441 2 4 8 4 16 336 7 20 19 361 6 2 12 36 4 380 8 22 22 484 8 5 40 64 25 484 Total 2520 167 218 208 2071
|Root Cause Analysis|
Root causes are specific reasons that contribute to medical errors. They cause mistakes that lead to great patient harm (adverse events). Usually they can be identified. Examples: Using a wrong calculation factor Neglecting to use directions for complicated tests Reporting the wrong test result Using outdated reagents Testing clotted or partially-filled samples Diluting a test sample incorrectlyIn most cases, management has the authority and means to resolve root causes. Root Cause Analysis also recommends actions to prevent reoccurrence of an adverse event.
|Specificity Example: Calculations (1)|
Determining the specificity of the experimental method will help show if the test is worthwhile.Using the equation for specificity, we insert the following numbers: 100 True Negatives Divided by (100 True Negatives + 275 False Positives) Times 100 or (100 ÷ (100 + 275)) x 100. The specificity for the "Experimental" method is 26.7%.
|Sensitivity Example: Calculations (1)|
Let's return to our experiment method from the previous example. This time, we'll calculate the sensitivity.The experimental method produced 600 true positives and 25 false negatives. By inserting these numbers into the sensitivity equation, we get (600 ÷ (600 + 25)) x 100.Thus, the experimental method has a sensitivity of 96%.
|Sensitivity Example: Calculations (2)|
The tried-and-true method also had 600 true-positive results but had 50 false-negative results. Once again inserting these numbers into our equation, (600 ÷ (600 + 50)) x 100, we find that the tried-and-true method has a sensitivity of 92%.
|CUSUM Example: Plotting Control Data|
To illustrate the use of CUSUM in the laboratory, we'll use daily control values for glucose testing. In the example laboratory, testing is not performed on weekends, explaining the lack of data on days 1, 7, and 8.First, we'll list daily control values under "daily results." Then, we'll calculate mean by using formula A. Next, we can find the difference from the mean for each result, and square that result for the two relevant columns. Using all of the squared differences from the mean, we can find the standard deviation using formula B. Using the mean from formula A and the standard deviation calculations from formulas B and C, we can plot our data points on the Levey-Jennings chart. Formula D helps us calculate the coefficient of variation (CV), which expresses SD as a percentage of mean value and is more reliable for comparing precision at different concentration levels. The lower the CV the greater the precision.
|Specificity Example: Calculations (2)|
To calculate the specificity of the tried-and-true method, we'll use these numbers: 325 True Negatives Divided by (325 True Negatives + 25 False Positives) Times 100 or (325 ÷ (325 + 25)) x 100. The specificity for the tried-and-true method is 92.9%.
|What is internal quality control?||View Page|
Numerous studies have shown that, if administered correctly, RhIg is effective at preventing D immunization. To work, RhIg must be given in sufficient dose, and it must be given before Rh immunization has begun.Unfortunately, despite RhIg's proven efficacy, some women still make anti-D in the perinatal period. Such 'failures' are mainly (but not totally) due to human error. Examples of how women may still produce anti-D some 40+ years after the implementation of RhIg prophylaxis: Immunization to D occurred before RhIg was administered, e.g., before 28 weeks gestation*; Immunization to D occurred after the administration of RhIg at 28 weeks and before delivery because an antenatal FMH occurred that was too large for residual passive anti-D to give protection; Female was already immunized from a prior pregnancy but anti-D was too weak to be detected in antibody screen tests prior to RhIg administration; RhIg dosage was insufficient to clear a larger fetal bleed at delivery (e.g., FMH screen or quantification was not done or a false negative occurred); Incorrect calculation of RhIg dosage; RhIg administered too late , e.g., well after 72 hours of delivery; Antenatal RhIg not given, e.g., mother had no or limited access to prenatal care, or did not seek it, and a FMH occurred during pregnancy; Failure of physician to carry out prenatal blood testing; RhIg not given due to laboratory clerical or technical error in Rh typing the mother or child; RhIg not given in cases such as abortions, ectopic pregnancies, and trauma (e.g., car accidents). * Because anti-D production before 28 weeks is rare (the order of 0.24% to 0.31%), RhIg's use earlier in pregnancy is not recommended. It is not cost effective and would expose most women to an unneeded blood product.
|For those facilities that in the interest of safety use a special calculation for RhIg dosage, regardless if they round up or round down, they always add one vial.||View Page|
The basic laboratory skills that you will need to do a semen analysis include: Use of a microscopePerformance of manual cell countsMeasuring volumeMeasuring pHMeasuring viabilityKnowledge of OSHA regulations for handling potentially infectious human fluids
If the specimen is more viscous than normal, it may be difficult to dilute it or to load it onto counting chambers in the undiluted condition. In this rare situation the semen may need to be manipulated to reduce the viscosity before a count is done. One method to do this is to repeatedly pipet the specimen up and down with an equal volume of culture medium. Care must be taken to avoid foaming. Other methods include enzyme digestion, for example with bromelain at a concentration of 1 gm / liter, or addition of a small amount of emulsifier, such as Alevare or chymotrypsin. Any manipulation of this type must be recorded on the report sheet. Calculation of the number of sperm per milliliter will also have to be corrected for any dilution.