lab math

how is the volume of fetal whole bleed

[(# of fetal cells ) / 2000 ] * 5000

how do you determine the correct number of RhIG vials to administer?

(volume of fetl bleed mL)/ 30 mL = # of vials + 1 for safety factor

rounding rules for determining RhIG vials

• if decimal greater than 0.5, round up by one

• if decimal less than 0.5, round down

what is the Hardy-Weinberg equation

p² + 2pq + q² =1

so p+q =1

what is the equation that can be used to estimate the number of units needed to screen in order to find compatible units

( # of compatible units needed) / (% compatibility)

how many units are needed to screen to find 2 units negative for E antigen?

• the % population that is E negative is 70%

2/0.70 = 2.8→ need to screen around 3 units

context: patient has developed anti-Fya and anti-K

how many units need to be screened in order to get 3 compatible units

• 34% negative for Fya

• 91% negative for K

3/ (0.34 +0.91) = 3/31 = 0.6 → 10 units

a full dose of RhIG protects against __ of Rh positive packed red blood cells

15mL

a full dose of RhIG protects against __ of whole blood

30 mL

how much RhIG are usually admistered antepartum

usually 1 dose

if a fetal blood screen has a negative result, how many doses of RhIG should be given

one dose

equation to determine RhIG dose with % fetal cells

(% fetal cells) * 50 / 30 mL → add 1 for safety

MCV formula

Hct/RBC * 10

MCH formula

Hgb / RBC *10

MCHC formula

Hgb/Hct * 100

RDW-CV formula

(SD of MCV *100 ) / mean MCV

RDW-SD

width of peak at 20% height

hemocytometer formula

(#cells counted ) (1/ total volume) dilution factor (d_f)

equation to get total volume for hemocytometer calculations

volume * # squares counted

how to determine the volume of one square in a hemocytometer

length x width x depth

total volume counted for WBC hemocytometer count

0.9 mm3

total volume counted for platelet hemocytometer count

0.1 mm3

formula for corrected WBC count due to nucleated RBCs

(WBC count * 100) / (100+ # of nRBCs)

calculation for % reticulocytes

(# of retics in 1000 RBCs) / 10

absolute reticulocyte calculation

(# of RBCs ) * (% retics)

corrected reticulocyte equation

(% retics * patient Hct) / 45

RPI (reticulocyte production index) calculation

corrected retic count / maturation time (usually 2)

INR (international normalized ratio) calculation

(patient result / mean of reference range) ^ ISI

creatinine clearance equation

(U * (Volume 24 hr / 1440 min/24 hr) ) / P

U = [] of urine creatinine mg/dL

P = [] of plasma creatinine mg/dL

normal creatinine clearance

120 mL/min for adults

creatinine clearance correction for kidney mass (kidney mass proportional to body size) calculation

[ (U * V) / P ] x (1.73/A)

A= body surface area

eAG formula

(28.7 x A1c) - 46.7

osmolality equation

2Na + (glucose / 18) + (BUN / 2.8)

pH formula

pKa + log [HCO3] / [H2CO3]

anion gap with K+

[Na + K] - [Cl + HCO3]

anion gap without K+

Na - [Cl + HCO3]

what are the ways that concentration be measured

• w/w : weight per unit weight

• w/v : weight per unit volume

• v/v : volume per unit volume

what is the most accurate type of % concentration but is not often used in the clinical laboratory

w/w

what is the most commonly used concentration measuring method in the clinical laboratory

w/v - a solid solute is mixed with a liquid solvent

what conversions are relevant for concentration calculations

1 mL H2O = 1 gm H2O

1% = 1 gm /100mL

prepare 100 mL of a 0.5% NaCl solution

measure 0.5 gm NaCl and add H2O up to 100mL

describe v/v

when a solution has a liquid solute in a liquid solvent

changing concentration equation

V1*C1 = V2*C2

units on both sides must be equal

ratio-proportion procedure

(unit weight 1 / unit volume 1) = (unit weight 2 / unit volume 2)

cross multiply to solve

describe Molarity

a mole of a substance is the number of grams equal to the atomic or molecular weight of the substance

GMW = gram molecular weight

often used as a definition of a mole

GMW can be expressed as

1 Molar solution = 1 mole of solute / Liter of solution

what does Molarity (M) express

the number of moles of a substance in 1 liter (1000 mL) of solution

M=

#of moles/liter

what are other ways Molarity can be mathematically expressed

• M = (grams/liter) / GMW

• # grams/liter = GMW * M

• M = (% *10)/ GMW

• % x 10 = GMW x M

mmole to mole ratio

1 mmole = 1/1000 mole

what is Normality based on

same principle of molarity, but M is based on GMW and N is based on GEW (gram equivalent weight)

general rules of Normality compared to Molarity

• GEW of a substance = GMV / valence

• GEW is ALWAYS =< GMV

main Normality (N) equation

(# grams/liter) / GEW

other ways to express Normality

• # grams/liter = GEW * N

• N = (%*10) / GEW

  • % x 10 = N x GEW

conversion of Molarity to Normality

N= M x valence

M = N / valence

mg/dL means

mg / 100 mL

conversion from mg/dL to mEq/L

mEq/L = (mg/dL x 10) / GEW

conversion from mEq/L to mg/dL

mg/dL = (mEq/L * GEW) / 10

milli symbol and power

m

10^-3

micro symbol and power

u and 10^-6

nano symbol and power

n 10^-9

pico symbol and power

p 10^-12

femto symbol and power

f 10^-15

deciliter notation and multiple

dL 1/10

milliliter / milligram notations and multiple

mL / mg 1/1000

microliter and microgram notation and multiple

uL / ug 1/1,000,000

nanogram notation and multiple

ng 1/1,000,000,000

picogram notation and multiple

pg 1/1,000,000,000,000