Call volume surged in the SPDR Health Care Index Fund on Friday, but it wasn't necessarily bullish.

A block of 25,000 December 41 calls traded for $0.41 against previous open interest of just 1,037 contracts.

At first glance it appeared that the calls were sold. But just 90 seconds later, the largest trade in the stock went off: 600,000 shares sold for $38.80. That was a full $0.18 less than the trades immediately before and after. Given that the bid/ask spread on the options was just $0.03 and the options traded in the middle of that, it may very well be that that calls were bought against the short stock position.

In that case, we're looking at a neutral position that can profit if the XLV moves sharply in either direction. It will also make money if the actual volatility of the stock is more than that implied by the options.

XLV rose 0.31 percent to $38.84 on Friday. That was lower than Wednesdays close, but it did touch a new all-time high of $39.05 during the session. It's been trending higher for the last 11 months, having bottomed just above $30 in October.

Total option volume in the fund was 8 times greater than average.

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Volatility trade targets health care fund