When casts or other findings are seen on the microscopic examination of urine, it is often desired to know the number per mL. This can be calculated based on the microscopic and preparatory parameters.


Calculating the number of high power fields (40x or 50x objective) under a coverslip:

(1) diameter of high power microscopic field in mm

(2) area of microscopic field in square mm = π * ((diameter in mm) / 2)^2)

(3) area of coverslip in square mm = (width in mm) * (length in mm)

(4) number of high power fields per coverslip = (area of coverslip) / (area of microscopic field)


Calculating concentration of urine sediment:

(1) initial volume of urine in mL prior to centrifugation

(2) final volume of urine sediment after decanting of supernatant in mL

(3) concentration of sediment = (original volume in mL) / (final volume in mL)


Calculating number of high power fields per mL urine:

(1) volume of sediment placed under the coverslip in mL.

(2) equivalent volume of original unspun urine in mL = (volume under slip) * (concentration of sediment)

(3) number of high power fields per mL urine = (number of high power fields under coverslip) / (equivalent volume of original urine in mL)


concentration of formed element per mL urine =

= (number of formed elements per high power field) * (number of high power fields per mL urine)


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