MATH STUFF

Question 1

Approximately how many units do you need to screen if 3 units of Jkb-, Fya-,E- and c- are needed for a patient’s surgery the next day?

Answer 1

200 units

3 out of 200 willl be neg for the antigens

(0.18) (0.32) (0.26) = 0.014976 = 0.015 x 100 = 1.5

1.5/100 = 3 units needed / # of units needed to screen
# of units = 3x 100 / 1.5
# of units = 200

Question 2

A mom with anti-D was diagnosed with intrauterine HDFN, and fetus may require transfusion. Calculate the volume of blood to be transfused in an intrauterine transfusion (IUT), with a current fetal hct of 10%. The desired hct is 38%, fetus is estimated to be 800g. The unit to be transfused is Rh neg, CMV-, HbS- and has a hct of 80%.

Answer 2

Step 1) 800g / 0.14ml/g = 112ml

2) (112ml x (0.38-0.10)) / 0.80
= (112 ml x 0.28) / 0.80
= 31.36 ml / 0.80
= 39.2 ml to to be transfused

Question 3

Calculate the # of RhIg vials needed if the KB test result found 20 fetal cells out of 2000 cells total counted; maternal blood volume estimated at ~5000ml
A. 1
B. 2
C. 3
D. 4

Answer 3

C. 3

FMH = (20/2000) x 5000ml = 50ml
50/30 = 1.67 vials
Round up 1.67 vials = 2 + 1 = 3 vials

Question 4

Calculate the # of RhIg vials needed if the KB test result found 10 fetal cells out of 1500 cells total counted; maternal blood volume estimated at ~5000ml
A. 1
B. 2
C. 3
D. 4

Answer 4

B. 2

FMH = (10/1500) x 5000ml = 33.33 ml
#of vials = (33.33/30ug per dose) = 1.1 vials
Round down 1.1 = 1 vial + 1 

=2 vials RhIg to be given

Question 5

How many units are needed to be screened for a patient that needs 4 units of Fya- and Jkb-?
Prevalence: Fya = 68%, Jkb= 74%

Answer 5

Need to screen 48 units

Prevalence for antigen negatives: Fya= 32%, Jkb=26%

Step 1: (0.32) (0.26) = 0.0832 x 100 = 8.32

Step 2:  8.32 / 100 = 4 / # of units needed 
               # of units needed = (4)(100) / 8.32
               # of units needed = 48

Question 6

Determine the percentage of blood loss for a patient weighing 110 lbs who lost about 500ml of blood.

Answer 6

13%

Step 1: convert 110lb to kg = 110lb / 2.2lb/kg = 50kg
Step 2: use blood volume formula = (50kg) (75ml/kg)
= 3750 ml pt’s blood volume
Step 3: calculate % blood lost = 500ml blood lost / 3750 ml blood volume
= 13%

Question 7

How much blood is needed for an intrauterine transfusion for a neonate weighing 800g with a hematocrit of 15%? The target hematocrit is 30%, and the unit to be transfused has a hematocrit of 85%.

Answer 7

20 ml

Step 1: calculate hct increment = post hct - current hct = 0.30 - 0.15 = 0.15
Step 2: calculate IUT vol = (neonate w in g) (0.14ml/g) (hct increment) / hct of unit
= 800g x 0.14ml/g x 0.15 / 0.85
= 19.8 = 20 ml

Question 8

An RBC unit for an exchange transfusion needs to have a hematocrit of 40%. The RBC unit selected currently has a volume of 350 ml with a hematocrit of 80%. How much plasma is needed to be added to reach the desired hematocrit of 40%?

Answer 8

350 ml plasma to be added

Use formula V1C1 = V2C2

350 ml x 0.80 = V2 x 0.40
Total blood volume = V2 = 350 x 0.80 / 0.40
= 700 ml
Plasma to be added = V2 - 350 = 700 - 350 = 350 ml

Question 9

What is the maximum blood that can be collected in a 500 ml bag from a donor weighing 120lbs?

Answer 9

522 ml max blood collected

Step 1: convert lb to kg = 120lb/ 2.2 lb/kg = 54.5 kg
Step 2: calculate max volume to be collected = 10.5ml/ kg
= 54.5 kg x 10.5 ml/kg = 572 max blood collected
Step 3: subtract max volume by 50ml* = 572ml - 50 ml = 522 ml max blood collected

• subtract 50 if collecting in 500 ml bag or 45 if collecting in 450 ml bag (this is used in tubing and for infectious disease testing)

Question 10

What is a patient’s blood volume and plasma volume if he weighs 160 lbs with a hematocrit of 35%?

Answer 10

5452.5 ml blood vol and 3544 ml plasma vol

Step 1: convert weight to kg = 160lb / 2.2 lb/kg = 72.7 kg
Step 2: calculate blood vol = 72.7 kg x 75 ml/kg = 5452.5 ml
Step 3: calculate hematocrit = 1-hct = 1-0.35 = 0.65 ( this is % of plasma)
Step 4: calculate plasma vol = BV x hct from step 3 = 5452.5 x 0.65 = 3544 ml plasma vol

Question 11

A 65 kg patient has a hematocrit of 40%. What volume of plasma is needed for one volume plasma exchange?

Answer 11

2925 ml plasma needed

Step 1: find blood volume: 65 kg x 75 ml/kg = 4875ml
Step 2: find plasma volume: BV (1-hct) = 4875 ml (1-0.40)
= 4875 (0.60)
= 2925 ml plasma needed

Question 12

How many units of cryo is needed for a patient with suspected DIC, weighing 140lbs and a hematocrit of 35%, if his ordering physician wants to raise his fibrinogen count from 40 mg/dL to 125 mg/dL?

Answer 12

Need 18 units of cryo

Step 1: convert lb to kg = 140lb / 2.2 lb/kg = 64.1 kg
Step 2: calculate BV = 64.1 kg x 75ml/kg = 4806.8ml
Step 3: calculate PV = 4806.8ml (1-hct) = 4806.8 (1-0.35) = 3124.42ml
Step 4: convert ml to dL = 3124.42ml x 1dL/100ml = 31.2 dL
Step 5: calculate fib. count increment: 125 - 40 = 85mg / dL
Step 6: calculate # of units needed= (PV x fib count increment) / 150mg/dL*
= (31.2 dL x 85mg / dL) / 150 mg/dL per unit
= 17.68 = 18 units