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Household debt across Asia is raising red flags, particularly in Thailand and Malaysia, but the official data may not capture the full picture for families around the region. The official data can be worrying enough: Malaysia's ratio of household debt to income is 146 percent, while Thailand's is at 121 percent, based on mid-2014 data, up from 2007 pre-crisis levels of 139 percent and 93 percent respectively, McKinsey said in a report in February. Read More Debt bondage behind Hong Kong sex trade

"These debt ratios are similar to those in the United States and the United Kingdom," it said. "Given the lower income levels in those countries, this raises questions about sustainability of household debt." Off the radar But those figures don't provide the full picture of household indebtedness in the region, as not only are many types of debt going untallied, but it isn't clear how much debt simply moved into the formal sector.

For example, in Malaysia, the number of household borrowers from commercial banks per 1,000 adults was around 193 in 2004, but that grew to around 403 by 2013, while in Thailand, it rose to around 277 from around 143 over the same period, according to IMF data. It isn't clear whether those households are first-time borrowers or whether they've simply moved existing debt away from traditional money lenders, such as loan sharks, who typically don't file financial reports. But there are indications that informal borrowing is common across Asia. Read More Are Asian households over their head in debt?

Around 27 percent of Thais reported borrowing money, but only 19 percent borrowed from a financial institution and 2 percent went to an informal private lender, according to 2011 data from the Global Financial Inclusion (Findex) database, funded by the Bill & Melinda Gates Foundation. Findex plans to release updated data for 2014 later this month. The data for other Asian countries is even starker: In Malaysia, 33 percent borrowed money, but only 11 percent borrowed from a financial institution, while in Indonesia, 49 percent borrowed money, but only 9 percent borrowed from a financial institution. Sustainable or not? Whether some of the apparent growth in Asia's household debt is just a shift from the informal sector can be important for determining the sustainability of household finances as loan sharks in the region can charge annual rates exceeding 1,000 percent for short-term debt, significantly higher than microfinance and bank rates.