## Lab Math

**Calculation of "G" or RCF (Relative Centrifugal Force)**RCF is dependent on the speed of the rotor and the distance from the center of the motor drive shaft to the base of the sample tube. Manufacturers will give you the maximum speed and RCF of the rotor and its radius. For any speed other than maximum, you need to calculate the RCF.

If you do not know the radius of the rotor, you will have to measure this. Sometimes this may entail a little bit of guesswork in the case of an angle rotor. The radius is measured from the centre of the rotor to the point that would be the bottom of the sample tube. Take into account, inserts and any tube cushions.

**Converting RPM to g- force (RCF) and vice versa**

**Click to the link**

**Coefficient of Variation**Allows comparison of nonidentical data sets, i.e. two different procedures, etc., by expressing the standard

deviation of each set as a percentage of the mean. CV is expressed as a %.

The formula is: CV=(SD/X) x 100, where SD= the standard deviation of a procedure and

X= the mean.

Procedures with increasing CV values demonstrate decreased precision, since this reflects greater variability among the replicate samples.

**Slope-Intercept Formula**

**y = mx + b**

where m and b designate constants (the variable y is multiplied by the constant 1, which as usual is not explicitly written). The origin of the name "linear" comes from the fact that the set of solutions of such an equation forms a straight line in the plane. In this particular equation, the constant m determines the slope or gradient of that line; and the constant term b determines the point at which the line crosses the y-axis.

**Mean**

The mean is calculated by adding all of the values, and dividing by the number of values. The formula is:

For example, suppose you wanted to find the mean of the values 4, 6, 2, 8, and 5.

The mean is:

The mean is:

X = mean

n = the- number of data points in set (total number of measurements)

Σ = the sum of

Xi = each measurement

n = the- number of data points in set (total number of measurements)

Σ = the sum of

Xi = each measurement

**Standard Deviation**

The standard deviation (abbreviated s or SD) is calculated according to the following formula:

That is, calculate the deviation from the mean for each point, square those results, sum them, divide by the number of points minus one, and finally take the square root. For example, the deviations from the mean in the above example are -1, 1, -3, 3, and 0. The squared deviations are 1, 1, 9, 9, and 0. The standard deviation is therefore:

The

standard deviation will be larger if the data are spread out and smaller if the

data are closely clustered about the mean.

X = each data point

n = the number of data points in set (total number of measurements)

Σ = the sum of

S = standard deviation

√ = square root

X = mean

Xi = each measurement

(Urine creatinine X Urine volume) / (Serum creatinine X min. of duration) = (mL) / (min)

This value is then corrected for body surface area:

Creatinine Clearance = ((mL) / (min)) x ((1.73 m2) / (Patient's surface area (m2)))

Urine Volume (mL/24 hours) / 1440 minutes per 24 hrs x urine creatinine/ serum creatinine x 1.73/ patient’s surface area

Urine Protein (mg/dL) x urine volume (mL/24 hrs) x 1dl/100 ml

C = Concentration

C = 1.85 x0.001 (100-HCT) x volume of blood For a 4.5 ml draw, C = 1.85 (0.001) (4.5) (100-HCT)

C = 0.008325 (100-HCT)

C = 0.008325 (100-65)

C = 0.008325 (35) = 0.29 of sodium citrate needed 0.50 – 0.29 = 0.21 sodium citrate to be removed from a 4.5 ml tube

The total cholesterol to HDL cholesterol ratio (total chol/HDL) is a number that is helpful in estimating the risk of developing atherosclerosis. The number is obtained by dividing total cholesterol by HDL cholesterol. (High ratios indicate a higher risk of heart attacks, whereas low ratios indicate a lower risk).

The FTI tells how much T4 is present compared to the thyroxine-binding globulin. The FTI can help tell if abnormal amounts of T4 are present because of abnormal amounts of thyroxin-binding globulin.

% error = actual value - theoretical value X 100 theoretical value

standard deviation will be larger if the data are spread out and smaller if the

data are closely clustered about the mean.

X = each data point

n = the number of data points in set (total number of measurements)

Σ = the sum of

S = standard deviation

√ = square root

X = mean

Xi = each measurement

**Creatine Clearance**(Urine creatinine X Urine volume) / (Serum creatinine X min. of duration) = (mL) / (min)

This value is then corrected for body surface area:

Creatinine Clearance = ((mL) / (min)) x ((1.73 m2) / (Patient's surface area (m2)))

**OR**Urine Volume (mL/24 hours) / 1440 minutes per 24 hrs x urine creatinine/ serum creatinine x 1.73/ patient’s surface area

**24 Hour Urine Creatinine**

Urine creatinine (mg/dL) x urine volume (mL/24 hrs) x 1dl/100 ml**24 Hour Protein**Urine Protein (mg/dL) x urine volume (mL/24 hrs) x 1dl/100 ml

**Corrected Ratio of blood to anticoagulant (the citrate concentration must be adjusted in patients who have hematocrit values above 55%.**C = Concentration

C = 1.85 x0.001 (100-HCT) x volume of blood For a 4.5 ml draw, C = 1.85 (0.001) (4.5) (100-HCT)

C = 0.008325 (100-HCT)

**Example: HCT= 65 in a 4.5 ml draw**C = 0.008325 (100-65)

C = 0.008325 (35) = 0.29 of sodium citrate needed 0.50 – 0.29 = 0.21 sodium citrate to be removed from a 4.5 ml tube

**Chol/HDL Ratio**The total cholesterol to HDL cholesterol ratio (total chol/HDL) is a number that is helpful in estimating the risk of developing atherosclerosis. The number is obtained by dividing total cholesterol by HDL cholesterol. (High ratios indicate a higher risk of heart attacks, whereas low ratios indicate a lower risk).

**Chol/HDL ratio = Chol/ HDL****Free Thyroxine Index Formula**The FTI tells how much T4 is present compared to the thyroxine-binding globulin. The FTI can help tell if abnormal amounts of T4 are present because of abnormal amounts of thyroxin-binding globulin.

**FTI = T3U x T4**

100100

**% Error**% error = actual value - theoretical value X 100 theoretical value