The interpretation of results
It can take considerable effort, and expense, to produce what may seem to be just numbers on pieces of paper or on a computer screen. Understanding what these numbers mean is of crucial importance if the correct diagnosis is to be made, or if the patient’s treatment is to be changed.
How biochemical results are expressed
Most biochemical analyses are quantitative, although simple qualitative or semi-quantitative tests, such as those for the presence of glucose in urine, are commonly encountered methods used for point of care testing. Many tests measure the amount of the analyte in a small volume of blood, plasma, serum, urine or some other fluid or tissue. Results are reported as concentrations, usually in terms of the number of moles in one litre (mol/L) (Table 3.1).
Table 3.1
| Mole | Abbreviation | Definition |
| Millimole | mmol | ×10−3 of a mole |
| Micromole | µmol | ×10−6 |
| Nanomole | nmol | ×10−9 |
| Picomole | pmol | ×10−12 |
| Femtomole | fmol | ×10−15 |
The concept of concentration is illustrated in Figure 3.1. The concentration of any analyte in a body compartment is a ratio: the amount of the substance dissolved in a known volume. Changes in concentration can occur for two reasons:
Fig 3.1 Understanding concentrations. Concentration is always dependent on two factors: the amount of solute and the amount of solvent. The concentration of the sugar solution in the beaker can be increased from 1 spoon/beaker (a) to 2 spoons/beaker by either decreasing the volume of solvent (b) or increasing the amount of solute (c).
