The half-time of nickel in serum is similar to that in urine. Values ranging from 20 to 34 hours have been reported for workers exposed to soluble nickel compounds via inhalation (Tossavainen et al., 1980). A half-time of 11 hours was observed in human volunteers orally dosed with soluble nickel sulfate hexahydrate (Christensen and Lagesson, 1981).
Just as in the case of urinary nickel, serum nickel levels cannot be used as indicators of specific health risks. They are of most use when interpreted on a group basis. Serum or plasma nickel levels can provide an indication of recent exposure to nickel metal powder or relatively soluble nickel compounds. Likewise, elevated serum or plasma nickel levels in individuals exposed solely to less soluble nickel compounds may reflect significant absorption that could be indicative of a corresponding long-term increase in workplace exposures. Normal serum or plasma nickel values in workers exposed to less soluble forms of nickel do not necessarily indicate an absence of exposure to such forms. Because serum nickel is not a good predictor of health risks, conclusions regarding the presence or absence of risk should not be drawn from such data.
Serum and plasma concentrations of nickel tend to be similar, whereas whole blood concentrations have been found to be approximately twice that of serum and plasma (Baselt, 1980). Pre-or post-shift sampling is typically performed (Sunderman et al., 1986), although in some instances, both morning and after-work samples have been taken in the same workers (Høgetveit et al., 1980). Nickel concentrations in the serum and plasma of healthy non-exposed individuals range from 0.05 to 1.1 µg Ni/L (Sunderman et al., 1986). Like urine nickel samples, it is important that blood samples be analyzed by a reputable laboratory. Analysis should be reported as mg Ni/100ml or µmol Ni/100ml. If a biological monitoring program is instituted, blood nickel samples should be collected annually (Hall, 2001).
As with urinary nickel measurements, there are both advantages and disadvantages to using serum nickel concentrations in biological monitoring programs. The primary disadvantages of measuring serum or plasma nickel levels are that the sampling technique is invasive and serum and plasma nickel levels are lower than urinary levels (Sunderman, 1989). The primary advantages are that serum and plasma samples are less subject to matrix variability fluctuations and to contamination from workplace dust.